Overview

in the spring and early summer, both aphid species infest young trees, water sprouts, and vigorous terminals on apple, pear, and quince. Unlike rosy apple aphids, which spend part of their life cycle on plantain, both green apple aphid and spirea aphid remain on apple year-round.

Aphid nymphs and adults suck sap from apple leaves, favoring rapidly growing terminal and water sprout foliage. Leaf curling indicates aphid presence, but causes little or no damage. Aphids excrete large amounts of honeydew which may collect on fruit and foliage. Black sooty-mold fungus can develop on honeydew, discoloring fruit.

Biology

• Apple aphid and spirea aphid overwinter as black, shiny eggs on the rough areas (leaf and pruning scars, terminals, and spurs) of the bark of the previous season's growth. Eggs hatch in spring and nymphs (all of which are females, called "stem mothers") mature while feeding on developing foliage.
• Aphid adults are a uniform yellowish-green to green color with black cornicles at the end of the abdomen.
• The "stem mothers" feed, mature, and produce another generation of live nymphs, all of which are females. This type of reproduction without mating is called parthenogenesis. Eventually, winged aphids ("alates") appear, and for the duration of the summer, the population consists of both winged and wingless parthenogenetic females that continue to produce live nymphs.
• In late summer, the winged aphids disperse to different apple trees or other host plants and produce nymphs that develop into true sexual forms. After mating with males, females lay overwintering eggs that hatch the following spring. the cycle then repeats itself.
• Apple aphids and spirea aphids are similar in appearance, but spirea aphids may remain active on apple trees later into the summer.
• A different aphid, the apple grain aphid, can become very abundant on buds in early spring, but it causes no damage to apples and soon migrates to grain and grasses for the summer. Apple grain aphids are green with a dark stripe on its back.

Monitoring

• Aphid monitoring should begin in June by checking at least 10 terminals and water sprouts per tree and 10 trees per block. Treatment threshold is 50% of vegetative terminals infested AND less than 20% of infested terminals with biocontrol agents present OR 10% of fruit with honeydew or aphids.

Management

• Limit nitrogen fertilization to the level necessary for optimum tree growth.
• Summer prune to remove water sprouts.
• Two predators offer excellent potential for biological control and can often be found among aphid colonies. Syrphid fly larvae are small, legless, tan-green mottled maggots and Cecidomyiid fly larvae are small, orange maggots. Both are voracious feeders, capable of consuming dozens of aphids before completing development
• If finding aphid populations above threshold, consider waiting one week and then check again for biocontrol agents. If treatment threshold is still exceeded, apply an insecticide.

Overview

Rosy apple aphid feeding results in stunting of new growth and may cause sooty mold to develop on fruit and leave. As they feed, rosy apple aphids inject a toxin with their saliva that causes the leaf to curl and the fruit to be distorted. Of the aphid species that can be found on apple trees, the rosy apple aphid causes the most severe damage and is the most difficult aphid species to control.

Biology

The aphid overwinters on apple trees as eggs laid on twigs, bud axils, or in bark crevices. The black eggs are 1/2 mm long and football-shaped. The overwintering eggs give rise to only female aphids which give birth to live young. Shortly after silver tip the eggs hatch. The nymphs' color changes from dark green to slightly purplish or dull pink with variable amounts of greyish-white wax bloom. The aphids continue to reproduce on apples until summer, then winged forms are produced which migrate to other hosts such as dock and narrow-leaved plantain to spend the summer. Recent evidence, however, shows that the biology of this pest has changed and populations in orchards may no longer need to go to the alternate host plantain but can breed continuously on apple. In the late fall, winged forms migrate back to apples and lay eggs in bark crevices and on twigs.

A cool, wet spring favors aphid development because it provides conditions unfavorable for parasites and predators of aphids.

Damage

These aphids cause a decrease in tree vigor because of foliage loss and damage to the fruit through dwarfing, misshaping, and staining. The rosy apple aphid injects a toxin with its saliva that causes the leaf to curl and the fruit to be distorted. A single stem mother located on the underside of a leaf near the midrib will cause the leaf to fold almost as tightly as the outer wrappings of a cigar. The presence of only a few stem mothers can cause severe curling of all leaves surrounding an opening flower bud; within such curls, ideal protection is afforded to the rapidly developing aphids.

‘Cortland', 'Ida Red', and 'Golden Delicious' are the varieties most frequently showing fruit injury. Fruit adjacent to rosy apple aphid colonies is stunted, puckered at the calyx end, and ridged like a pumpkin.

Monitoring

Monitoring for rosy apple aphid is possible after egg hatch begins since the eggs of apple grain aphid and apple aphid are identical to rosy apple aphid eggs. Starting at early pink, select 5 to 10 trees per block. Sensitive varieties such as ‘Cortland', 'Ida Red', and 'Golden Delicious' should be selected if present. For 3 minutes, on each tree, count the number of fruit spurs showing curled leaves. The presence of more than one aphid-infested cluster per tree justifies an insecticide treatment to prevent fruit injury. Samples should be taken from the upper parts of the canopy on the inside of the tree where rosy apple aphid colonies are most common.

Management

The green apple aphid, apple-grain aphid, and rosy apple aphid overwinter as eggs on twigs and bark crevices of apple trees. A delayed dormant oil application between green-tip and half-inch green controls newly hatched aphids.

Before leaf curling, an organophosphate insecticide or a 1 to 2 % application of insecticidal soap or summer horticultural oil can provide effective control of these aphids. Thorough coverage is essential. After petal fall, because the curled leaves protect the aphids, then the best control will be achieved with a systemic insecticide. Some insecticide options include Admire Pro and Movento (active ingredient: spirotetramat*, at a rate of 6 to 9 fl. Oz). 

*Spirotetramat is an insecticide derived from tetramic acid, a systemic material, for the control of sucking insects in their juvenile, immature stages, including aphids, scale insects, and whitefly. It produces growth inhibition of younger insects, reduces the ability of insects to reproduce, resulting in mortality. Spirotetramat is harmless to slightly harmful to beneficials such as hoverfly larvae, spiders, predatory bugs, wasp parasites, lady beetles and lacewings.

Overview

WAA is a reddish brown aphid covered with a white wax mass produced by specialized dermal glands. This wax mass gives the insect its characteristic woolly appearance. WAA have a complex life cycle that can involve overwintering either on apple or elm. Once on apple they move to feeding sites on roots or above ground. Root feeding produces knotty galls, and extensive feeding severly taxes the root system. Unfortunately, the above-ground WAA population is not a reliable indication of the root-feeding population. Above ground, crawlers settle in bark crevices, pruning cuts, wounds, leaf axils, and occasionally the stem or calyx of fruit. Black sooty mold fungus can develop on WAA honeydew.

Biology

• WAA overwinter as eggs on elm trees. In early spring, wingless females remain feeding on elm for 2 generations. Winged females are then produced and migrate to apple trees late in June.
• Once on apple, 'crawlers' are produced that spread throughout the tree. Several generations are produced on apples each summer. Large nymphs have a purplish body, concealed by tufts of "wool", which are actually fine wax strands.
• In the fall, winged forms are again produced that migrate back to elm and deposit overwintering eggs.
• Colonies can persist on apple roots throughout the year.

Monitoring

• Monitor for WAA in mid-late summer when, if present, colonies of nymphs or adults become most visible.
• Because of poor coorelation of above and below ground populations, there is only a tentative treatment threshold of 50% of pruning wounds.  Sample 10 possible infestation sites per tree on at least 10 trees per block.
• Should WAA infestations appear on substantial numbers of leaf axils of terminals or fruiting spurs, treatment may be warranted to reduce possible injury to developing buds.

Management

• WAA are resistant to many commonly used insecticides. Apply an effective insecticide in summer if warranted.
• Best control is obtained when insecticide is applied in July when small WAA colonies appear on periphery of canopy, but this is before colonies are easily visible.
• Some insecticides can be applied to soil to manage WAA infesting roots.

Overview

Female AM deposit single eggs under the skin of apples and, once hatched, larvae tunnel through apple flesh leaving brown trails. Egg-laying punctures are difficult to find unless the fruit is heavily attacked, as are most apples in an abandoned orchard.

Biology

• Adult AM is slightly smaller than the common house fly, with a bright white spot at the center of the dorsum (back), 4 black wing bands (3 of which look like letter F), and 3 or 4 white stripes on the abdomen. Mature larvae are 3/8 inch long, legless, white, peg-shaped, legless larvae.
• Apple maggot flies overwinter in the soil as pupae, and emerge as adult flies in June - July. They migrate to apple trees from unsprayed or abandoned trees and are known to migrate for at least half a mile. Once adults emerge from the pupae in the soil, they feed and mate. About 10-14 days after adult emergence females start depositing their eggs. Larvae feed for 3-4 weeks before leaving fruit and entering the soil.
• Activity usually ceases in late August or early September but can extend into October on late cultivars.
• There is one generation per year.

Monitoring

• AM adult flies can be monitored using sticky coated red spheres that mimic ripening apple fruits or with yellow sticky boards which act as a leaf mimic. The addition of an apple odor-based 5-component lure (commercially available at Trece, Inc.) increases AM trap captures.
• Set out traps in late June at the rate of 1 trap per 3-5 acres, but not less than 3 traps per block. Place traps near the block periphery, 1 or 2 rows in from outermost row. Remove any leaves or fruit touching the traps.
• Apple varieties most susceptible to maggot attack are Wealthy, Cortland, Gravenstein, Red and Golden Delicious, and early sweet or subacid varieties. However, AM will attack any variety.

Management

• Recommended treatment threshold is an average of 2 AM per unbaited trap or 5 AM per baited trap.
• Trap captures for a week following insecticide treatment are ignored. Subsequent sprays can be applied once the threshold is reached again.

Overview

Several species of borers attack apple trees in New England, especially young trees. Dogwood borers are probably most damaging, but roundheaded apple tree borers, apple bark borers, flat-headed apple tree borers, and leopard moths can also be found. Black stem borers, a tiny bark beetle, has recently been attacking stressed apple trees in New England.

Biology

• Dogwood borers and apple bark borers are small wasp-like moths that lay eggs in bark crevices, primarily in burr knots and callus tissue around graft unions. Caterpillars grow up to 3/4 inch long, with an orange tinge. Caterpillars bore in bark, not wood, producing reddish frass on bark surface. Adults fly from mid-June through late August with peak flight in July. Trees with many burr knots (such as M9) are most heavily infested.
• Roundheaded apple tree borers are striped long-horn beetles about 5/8" long that emerge during the month following Petal Fall. Most egglaying occurs from late June to early August, and usually within a couple of hundred yards of where the female emerged. Larvae tunnel through trunks until completing the 2-3 year life cycle.
• Flat-headed apple tree borer is a dark/brown beetle belonging to the family Buprestidae. Adults are about 1/2" long with a metallic luster. They are primarily active in June and July on the sunny sides of trees. Eggs are deposited in bark crevices. Sinuous trails in the bark are visible without cutting into the tree. Eventually, the grubs bore into the wood, leaving tunnels that are oval in cross-section. Grubs are legless with a broad, flattened head end and a cylindrical body. Weakened, stressed or strongly leaning young trees are most frequently attacked.
• Leopard moth (Zeuzera pyrina), lay eggs in bark crevices in July and early August. Larvae bore into the bark and quickly move into the wood. They are usually first noticed because of the moist, fibrous droppings that are pushed out of tunnels. Caterpillars are white or pink with a dark head, and up to 2" long. The life cycle spans 2-3 years.
• Black stem borer is a very small – about 2 millimeters – ambrosia beetle (Xylosandrus germanus) that attacks stressed and apparently healthy trees, and in particular young trees, with trunk diameters of less than 2.5 inches. The insect is rarely seen outside of its galleries and only females emerge from the galleries they create to infest new trees. Signs of infestation include round entrance holes that are approximately 1 millimeter in diameter, toothpick-like strings of compacted boring dust and frass emerging from the holes, and sometimes weeping or oozing of plant sap from the holes.

Monitoring

• Look for signs of black stem borer infestation within 1 meter of the ground and use a simple trap to capture females. Cut two to four windows in the body of a plastic 1- or 2-liter bottle that has a cap. Hang it in the orchard upside down at a height of 1.5 to 3 feet, near wooded areas or in low areas where trees are prone to cold injury and where there are trees with signs of infestation.

  Bait the trap with ethanol using one of the following three methods:
  1. Squirt about a quarter cup of ethanol-based hand sanitizer (unscented) into the cap end (bottom) of your trap.
  2. With the bottle capped, pour in a cup of cheap vodka through one of the holes made in the side of the trap.
  3. Purchase a ready-made ethanol lure to hang inside the trap and fill the bottom of the trap with soapy water.
  If using hand sanitizer, traps must be checked daily because the sanitizer will form a crust on the surface after 24 hours. If using vodka or a purchased lure, traps should be checked at least once per week. Beetles are very tiny and require the use of a microscope and training to identify them correctly to species.

• Leopard moth adults can be monitored with pheromone traps.

Management

• Refer to the spray table for Summer Sprays.  One course spray of Assail to trunk between pink and mid-June. If fresh borer activity found in early July, spray Assail before early August.
• Dogwood borer management can be aided with mating disruption dispensers.
• For black stem borer management, apply insecticide when adult beetles are first caught in traps. Once beetles are inside trees, insecticides are ineffective because larvae do not feed on plant material.

Overview

BMSB is an invasive stink bug that feeds on a wide variety of host plants, including a variety of fruits (e.g., apples, stone fruits including peaches and apricots, figs, mulberries, citrus fruits and persimmons), vegetables (e.g., beans, corn, tomatoes and soybeans) and many ornamental plants and weeds. BMSB is currently distributed in 43 US states and 4 Canadian provinces.

BMSB is considered to be a landscape-level threat. This means that adults frequently switch between cropped land (agronomic crops, fruits, vegetables, ornamentals) and wooded habitats. BMSB nymphs and adults feed by inserting their piercing-sucking mouthparts into fruit, nuts, seed pods, buds, leaves, and stems and appear to prefer plants bearing reproductive structures. Their mouthparts can penetrate very hard and thick tissue, such as the hazelnut hull.

Biology

During the winter months, BMSB enters a type of hibernation called diapause. During this time adults do not feed and do not reproduce. Overwintering takes place in forested areas as well as inside houses and other buildings. In the spring, BMSB adults emerge from overwintering sites (houses, barns, storage buildings, and dead trees) and become active on nearby crops during warm sunny days. In the spring and throughout the summer, adults feed, mate, and lay eggs.

Monitoring

Commercially available traps and pheromone lures for BMSB monitoring provide valuable information on the presence/absence of BMSB and also help to decide if insecticide treatments are needed to manage this pest. Ag-Bio, Inc. (http://www.agbio-inc.com), Great Lakes IPM (http://www.greatlakesipm.com), Trece, Inc. (http://www.trece.com) and Sterling International are some of the companies that sell monitoring systems for BMSB. Monitoring for BMSB can start in late-May and needs to continue until early- or mid-October.

Monitoring devices.

• Black pyramid traps. Stink bugs, including BMSB, are visually attracted to tree silhouettes. The trap recommended for monitoring is a black pyramidal trap, which represents trunk mimic, coupled with a capturing device.
• Double-sided clear sticky cards. Researchers have found that double-sided clear sticky cards (6 x 12 inches), attached to a wooden pole, can be used for monitoring purposes. Cards are easier (and cheaper) to deploy than black pyramid traps.

Pheromone lures: Various companies are now marketing the male-produced aggregation pheromone of BMSB. Some pheromone lures incorporate the pheromone of multiple stink bug species, including BMSB. Therefore, efforts need to be made to correctly distinguish BMSB from other similarly-looking stink bugs.

Thresholds. Insecticide applications to apple orchards are recommended when a cumulative threshold of 10 BMSB/trap is reached. After the spray, the threshold is reset and subsequent trap accumulations reaching 10 adults per trap will trigger successive management sprays as the season progresses. This threshold is likely to work in peach orchards as well.

Management

Insecticide sprays is the most effective control method for BMSB. It is important to select effective insecticides given that adult BMSB are hard to kill. Whenever possible, target the nymph stage, as nymphs are more sensitive to insecticides than adults. Multiple applications may be needed with re-infestation.

The overwintering generation of BMSB tends to be more susceptible to insecticides than the summer generation. Therefore, products with the best effectiveness against this pest should be used later in the season.

Insecticides should be rotated among products in different classes with different modes of action to delay the onset of resistance to pesticides.

Overview

Larvae cause two types of fruit damage: deep entry, where larvae burrow down into the core of fruit, pushing frass out as they go; and shallow entry where feeding occurs, but no tunneling is present. Both forms of damage render fruit unmarketable. Second generation larvae cause the most damage. 

Biology

• Codling moth overwinters as a full-grown larva. Pupation occurs during bloom. First adults emerge at 150 DD, base 50 ℉., when counting from January 1. Warmer spring temperatures can accelerate the growth of codling moth, leading to earlier developmental milestones (like egg-laying and hatching).
• Newly hatched larvae are pale yellow with a black head, twice the width of its body. Mature larvae are pinkish-white with a brown head.
• Adult codling moth is gray-brown with alternating lighter gray and white bands across wings. Wings are marked at the back end by a coppery area that helps distinguish codling moth from other similar moths.
• Females can lay up to 100 eggs. Early season eggs are generally laid on leaves whereas later generations are usually laid on fruit.  There are usually 2 generations in New England.      

Monitoring

• Pheromone traps should be hung by bloom, on the north side of the tree at eye level. Hang traps in orchard areas where moths are most likely to enter from alternate host sites. Check traps twice a week and begin accumulating degree-days (base 50) after sustained catches in pheromone traps (biofix).
• First insecticide applications should be made ~ 250 DD (base 50) after biofix. First insecticide applications for the second generation should be made at about 1,400 DD to 1,600 DD, using the same biofix as previous spray timing.

Management

• Remove abandoned apple and pear trees, where practicable. Trunk banding can be a useful method of reducing codling moth pressure. Cardboard wrapped around trunks before larvae move to cocooning sites will cause them to pupate on the cardboard, which is subsequently removed and destroyed prior to adult emergence. Hot water treatment of storage bins can destroy a number of overwintering larvae.
• Mating disruption, set up before bloom, can be an effective way to reduce codling moth populations. Mating disruption is also needed in July for the second generation. Plan on supplementing mating disruption with insecticides. Using mating disruption in conjunction with insecticides is especially important for orchards with recent history of CM fruit injury or in the first year of a disruption program.
• Many insecticides are effective against codling moth when applied against newly hatching larvae. Resistance to pyrethroids and organophosphates, however, has been found in many areas of the Northeast.

Overview

EAS larvae feed under apple skin producing a heavily russetted, winding scar often seen on mature fruit at harvest.

Biology

• EAS overwinter as mature larvae in the soil. Larvae pupate and adults emerge when apples buds are in Pink stage.
• Adult EAS are clear winged, fly-like insects about 1/3 inch, dark brown above, and orange to yellow below.
• After feeding on apple pollen, EAS females cut slit into calyx end of tiny, developing fruit and insert an egg.
• Newly hatched larvae burrow just under apple skin leaving winding scar. (By harvest this scar is visible as a heavily russetted, winding scar.)
• If not controlled, larvae migrate to a second fruit and tunnel to the core. Frass can usually be seen on the surface of these apples, which drop to the ground by July. Mature larvae are 1/2 inch long, yellowish-white, and posses a pair of legs on each body segment.
• Full-grown larvae enter the soil where they remain until the following spring.

Monitoring

• EAS damage occurs more frequently when bloom time is extended and petal fall insecticide applications are delayed.
• White sticky traps placed before bloom can help determine the need for EAS insecticide at Petal Fall. Traps should be placed near blossoms at head height on the south side of at least one tree per 3 acres. Insecticide application may be warranted if more than an average of 6-9 EAS per trap are captured by Petal Fall in a block that received prebloom insecticide (or 4-5 in a block that did not receive prebloom insecticide).

Management

• Generally insecticides applied at Petal Fall adequately control EAS. Insecticide application is directed at early, superficially-burrowing larvae. Since apple varieties enter Petal Fall at different times, separate Petal Fall treatments may be needed.
• Prebloom insecticide for EAS is not needed except possibly for blocks where Petal Fall insecticide has historically not given satisfactory control.

Overview

Green pug moths have been found in New England since the 1990s. The yellow-green larvae are inchworms that bore into flower buds at bud break and feed, causes blossoms to abort. One larva can damage several flowers and, where numerous, can significantly reduce fruit set.

Biology

• GPM overwinter as eggs on apple trees, hatch at bud break, and enter buds to feed. Young larvae are olive green with black heads and look like winter moth young larvae.
• Larger GPM larvae are green and develop a dark red-brown stripe along the back.
• Most larvae finish feeding by Petal Fall, pupate in folded leaves, and emerge as adult moths in June and July.

Monitoring

• Examine flower buds for caterpillars at Tight Cluster to early Pink. Tentative treatment threshold is 6 or more GPM larvae per 100 fruit clusters.

Management

• Apply insecticide at early Pink if exceed threshold.

Overview

White apple leafhoppers (WALH) and rose leafhoppers (RLH) feed on the underside of leaves producing small, whitish spots on the upper leaf surface. This "stippling" may cover the entire leaves and appear silvery. Leafhopper feeding can reduce tree vigor, but of more concern is the accumulation of LH excrement on apple surface. The LH leave dark, "tar spots" and is difficult to remove.

Potato leafhoppers (PLH) do not overwinter in here, but migrate north with summer storms, usually reaching New England in mid June. PLH nymphs and adults feed primarily on immature leaves and actively growing shoots in the outer part of the canopy. Leaves injured by PLH feeding turn yellow on edges, cup upward, and later turn brown or scorched. On mature trees, PLH damage may not be significant, but feeding on young trees stunts shoot growth.

Biology

• WALH overwinter as eggs beneath tree bark. Hatching begins just before Bloom and is completed in 10-14 days. Nymphs migrate to leaf underside and feed, advancing into adults by mid-late June. These adults deposit eggs on leaves in July which hatch in early August, producing adults in August and September.
• RLH overwinter on rose species such as cultivated and multiflora rose. First-generation RLH adults migrate into orchards from nearby multiflora rose in early-mid June. Second-generation adults, present in July and August, deposit eggs mostly in orchards. In September, 3rd generation adults can cause extensive excrement spotting of fruit and be a nuisance to pickers before emigrating to rose bushes to deposit overwintering eggs.
• WALH and RLH adults look similar, but large nymphs of the two species can be distinguished with a hand lens. RLH nymphs have rows of small dark spots on their backs. Timing can also be used to distinguish the 2 species. LH found during Petal Fall are most likely WALH.
• PLH nymphs and adults are pale green. When disturbed, nymphs move rapidly in a sideways fashion.

Monitoring

• To monitor WALH and RLH, check 10 interior fruit cluster leaves per tree on 10 trees per block. The tentative treatment threshold is 3 WALH or RLH nymphs per leaf in June. However, growers who have had troublesome LH populations at harvest may want to use a lower threshold of 25 nymphs per 100 leaves in June.
• For PLH, sample the youngest shoot leaves in the outer canopy. Tentative threshold of one PLH per leaf.

Management

• LH have developed resistance to several insecticides. Insecticides are most effective against young nymphs. Older nymphs and adults are usually less easily controlled.

Overview

Apple blotch leafminer and spotted tentiform leafminer hosts include apple, pear, cherry, plum and quince, favoring apple leaves.The first 3 larval instars feed on tissue between the two epidermal layers of the leaf causing a translucent, 'sap feeding' mine that is visible only from the underside of leaf surface. The last 2 instars feed more extensively on leaf tissues and their 'tissue feeding' mines are visible from both the top and underside of leaves. 'Tissue feeding' mine on upper leaf surface contains numerous white dots.

Biology

• LM overwinter as pupae within mines on fallen leaves.
• Adults emerge in late April to early May and deposit eggs singly on leaf underside. Adults are 3/16 inch long, light brown moths that appear shiny in flight, with white spots that look like transverse bands when wings are folded. ABLM is nearly indistinguishable from STLM, but has forewings that are usually smaller and less heavily marked with white scales than STLM.
• Eggs hatch in 5-16 days and feed just below the lower leaf epidermis as 'sap feeders'. By late May larvae begin feeding just below the upper leaf epidermis, producing densely spotted mines visible on the upper leaf surface.
• There are 3 generations per year.

Monitoring

• Insecticide applications against 2nd generation mines normally not necessary unless mines exceed 1mine per fruit cluster leaf during 1st generation (by early June).
• Spur and leaf sampling for 2nd generation sap feeding mines allows effective timing of spray applications. Best time for insecticide application is when earliest 2nd generation mines are visible from the upper leaf surface (less than 10% have advanced to tissue feeding stage).
• Two parasitic wasps commonly attack LM larvae and can be found inside tissue feeding mines. Level of parasitism required for adequate LM biological control LM is unknown. Being aware of parasitoid development and behavior in orchards may aid in LM management.

Management

• If needed, spray insecticide when 2nd generation mines begin to advance to the tissue feeding stage. Selective insecticides allow parasitoids to substantially reduce larval populations.
• Second insecticide application may be needed.

Overview

European red mites (ERM) and Twospotted spider mites (TSM) are the two most common mite pests in New England orchards. Spider mites suck leaf fluids and chlorophyll, resulting in "bronzed" foliage. Slightly damaged leaves cause little or no adverse effect to crop. Extensive leaf bronzing results in decreased photosymthesis, often causing reduced fruit size, premature drop and reduction in fruit set the following year.

Biology

• ERM overwinter as eggs on smaller branches, twigs, and roughened bark of apple trees. Egg hatch begins at Tight Cluster, is about half complete by Pink, and is complete by Petal Fall.
• TSM overwinter as adult females primarily in orchard ground cover, where they feed on weeds and grasses. In mid-late summer, TSM migrate into fruit trees and feed on leaf undersides. There may be 10 generations per season.

Monitoring

• Mite injury during the weeks following Petal Fall can damage fruit crop. Monitor mite populations by examining underside of fruit cluster leaves through May and June. Action threshold is 1-2 motile (not eggs) mites per leaf or 30% of leaves with one or more mites.
• Starting in July, examine middle aged leaves for motile mites. Threshold for July is 5 mites per leaf. August 1-15 threshold is 7.5 mites per leaf.
• Mites tend to build up during periods of hot, dry weather. Mite populations tend to build up in "hot spots" rather than uniformly throughout a block. Hot spots tend to form on trees adjacent to dusty, dirt roads and in certain cultivars such as Red Delicious and Empire.

Management

• Oil is recommended at the 2-3 gal rate during the dormant period. Use 2 gal rate until Tight Cluster and reduce to 1 gal rate from Tight Cluster to Pink. Good coverage is essential (300 gal/A recommended).
• Many beneficial insect and mite species prey on pest mites and provide some level of biological control. Minimizing the use of pesticides harmful to mite predators is critical for conserving natural enemies and enhancing biological control of mites. A predator/prey ratio of 1:10 may provide adequate biological control.
• Several miticides are limited to 1 application per season to delay pesticide resistance developing.

Overview

OBLR attacks mainly apple and occasionally pear, peach, and cherry. Larvae feed on fruit skin, often close to the apple stem or where two apples are in contact. OBLR roll up leaves and hide in these shelters. Injuries occurring early in the season cause pronounced deformations of the fruit and are impossible to differentiate from the damage of green fruitworms. Late season fruit feeding causes small pits in the fruit surface that may go undetected until after long-term storage.

Biology

• OBLR overwinter as small larvae in trees. Overwintering larvae become active when trees break dormancy, and they complete their development about 3 weeks after Bloom. Larvae are yellowish-green to olive green; head and thoracic shield vary from tan to brown or blackish.
• Adults begin to emerge in late May or early June. Adult wings are beige, tinged with red. Forewings are crossed with oblique brown bands.
• Females can lay up to 900 eggs during a 7- to 8-day oviposition period. Eggs are green and deposited in a mass on upper leaf surfaces.
• Eggs hatch in about 10 to 12 days. Newly hatched first generation (summer) larvae move to and feed on tender growing terminals, watersprouts, or developing fruit. As these larvae reach the third instar, they display an increasing propensity to damage fruit. This generation takes almost two months to complete development.
• Adult flight of the second generation occurs in August, and the subsequent larvae hatch in August and September. The second-generation larvae feed primarily on leaves until they enter diapause, although they may occasionally damage fruit. Young larvae construct hibernation sites on twigs or bark to spend the winter.

Monitoring

• Scout for larval shelters during Bloom to Petal Fall. Examine 10 bud clusters per tree for  OBLR larvae and apply Bt insecticide if find more than 3% infested clusters.
• Monitor OBLR adults with pheromone traps and use a degree-day developmental model to time insecticide sprays against hatching larvae.

Management

• A Petal Fall insecticide spray should control overwintered larvae.
• Using the date of first OBLR capture as a biofix, use degree-day model to determine when OBLR eggs are hatching and most susceptible to insecticide. Apply insecticide starting at 360 DD (base 43F) after 1st adult trap capture. May need 2-3 sprays 10-14 days apart.
• Thinning of fruit and pruning water sprouts in midsummer is helpful in reducing fruit damage.
• OBLR may be difficult to control with insecticides, even with selective insecticides (Bacillus thuringiensis and insect growth regulators). Selective pesticides will preserve important natural enemies. More than one spray may be needed during the summer because of this species' extended flight and egg-laying periods.

Overview

Native to China, OFM is now found throughout much of the world. The adult OFM is approximately 1/4 inch (6.5mm) long and has a faint gray-brown salt-and-pepper pattern on its wings. Pupae are reddish-brown. Fully developed larvae are about 1/2 inch (12.5mm) long, pink to white in color. Eggs are about 1/32 inch (0.7mm) in diameter, yellow-white, and laid singly on leaves or twigs.

Biology

OFM overwinters as a fully-grown larva (caterpillar), on limbs or trunk. First-generation moths appear in May, and females lay their eggs on upper leaf surfaces, frequently on the terminal leaf of a young shoot. When the caterpillar hatches, it bores into the shoot primarily of stone fruits, causing the terminal to wilt or “flag”. Later generations attack the fruit of both stone fruit and apples. In the northeastern United States, the OFM usually has 3 generations (flights) per year, depending on weather conditions. As fruit develop the larvae will often enter near or through the stem end of stone fruit or calyx end of apple and bore directly into the interior of the fruit. OFM larvae do not feed on the seed; in contrast, codling moth larvae do feed on apple seeds.

Monitoring

Pheromone traps are available to monitor OFM activity and effectively time sprays. Traps are placed in the inside of the tree at eye level or higher. Follow manufacturers’ guidelines for proper trap and lure maintenance and replacement. One trap per ten acres is recommended for commercial orchards, with a minimum of two traps.

Place sex pheromone traps in early April and check at least three times a week until biofix (i.e., first sustained capture of two or more moths per trap) is established. Then, calculate and record degree days to determine the percent egg hatch for each generation and timing of insecticide sprays (see ‘management’ below). Continue to monitor traps weekly throughout the season. Pheromone-baited OFM traps will also catch lesser apple worm, so it will be important to know how to distinguish between the two.

The apple lesserworm is native to eastern North America. Adults are gray-brown moths quite similar to OFM but smaller (about 1/3 inch long with 7/16 inch wingspans) and with more brown-orange patches on the wings. When the moth is at rest, a gold band becomes evident across its back

Management

Several management options are available for OMF including insecticide sprays and mating disruption. Regardless of the type of OFM management method chosen, careful monitoring is critical to the success of IPM tools.

Chemical control of the OFM can be improved by using a degree-day model to establish optimum timing of insecticide sprays targeting newly hatched larvae since most insecticides are not effective at controlling adults. The most important spray against OFM on peaches is for the first generation. Keep in mind that there is a lag period for egg hatch after the moths fly. The first insecticide spray for OFM often coincides with petal fall, so sprays targeting plum curculio should also control the 1st generation of OFM.

Control measures for the second-generation egg hatch ought to occur at around 1,100 growing degree-days (base 45°F) after biofix.

With mating disruption, pheromone (sex attractant) dispensers are placed throughout the orchard. As the pheromone is released from the dispensers, male moths that normally use the pheromones to locate females become confused and fail to locate females. This interferes with the mating process. The densities of pheromone dispensers per acre depend on the formulation. Pheromone traps are used to evaluate the effectiveness of the mating disruption. If mating disruption is working, the pheromone traps should catch no moths. Mating disruption is only recommended for an orchard of 5 acres or larger in size.

If codling moth is also a problem in the same block, select a mating disruption material that releases pheromones of both species.

Overview

Plum curculio  (PC) is generally considered the single most destructive insect pest in orchards. The most recognizable type of wound caused by PC is the half-moon scar, produced by ovipositing females. Prior to depositing her egg, the female first uses her mouthparts to cut a small crescent-shaped flap in the fruit skin; then, she turns around to deposit an egg. When eggs hatch, larvae tunnel into fruitlets and begin to feed. Larvae complete four instars inside the fruit in about 16 days. PC-infested fruitlets generally drop to the ground prematurely. When an egg is not viable, or a female cuts into a fruit but does not deposit an egg, the scar remains and can be seen at harvest, often making the fruit unmarketable.

Biology

• Plum curculio (PC) is a snout-nosed beetle, aka a weevil. The adult is small, about 1/4 inch, mottled black, grey and brown. When handled it will often drop and “play dead”.
• The larva is a whitish, legless grub, and its feeding in fruitlets causes premature drop. Larvae then crawl out of fallen fruitlets into the soil and pupate. Adults emerge from the soil after ~16 days and feed within and outside of orchards until cold weather drives them into hibernating spots.
• Generally, commercial orchards do not have overwintering populations within their borders. Some studies, however, have shown that PCs can overwinter inside orchard blocks that are weedy in the fall.  Wild hosts (abandoned orchards, crab apples, etc.) near orchards provide habitat which allows adult PC to migrate into orchards before and after bloom.

Monitoring

• Fruitlets should be monitored beginning at about 5 mm diameter along orchard borders to determine if new injury is occuring. If fresh oviposition scars are observed, a first cover spray should be made to the entire block. Cool, wet weather will prolong PC activity. Continue to monitor for fresh scars. If more are found, a second cover spray targeting perimeter-row trees may be needed.
• Because PC immigration and oviposition period is affected by weather patterns after Petal Fall, insecticide coverage should be maintained until 308 DD (base 50F) from Petal Fall.
• A monitoring system that makes use of attractive lures, termed the ‘trap tree’ approach, has been developed. It involves baiting the branches of one perimeter-row tree with a synergistic two-component lure comprised of benzaldehyde, one synthetic component of flowers and developing fruit, in association with grandisoic acid, the synthetic PC pheromone. By examining the fruit solely on the odor-baited tree for signs of fresh PC injury this monitoring technique has proven effective at determining, on a timely manner, whether perimeter-row insecticide sprays are required against PC after the whole-block petal fall spray. Lures are commercially available and last for the entire PC oviposition period. For more information about the ‘trap-tree’ approach to PC monitoring, contact Jaime Pinero at jpinero@umass.edu.

Management

• Management of PC relies heavily on petal fall, first and second cover insecticide applications. The first insecticide application should be made to the whole orchard in order to control PC that have migrated into the inner part of the orchard.
• Additional insecticide applications may be necessary and can be limited to the outer two rows of trees.

• Kaolin clay (Surround WP) is an OMRI-listed material that can also be complementary to conventional management strategies. Applied in suspension in water, kaolin clay produces a dry white film layer of interlocking microscopic particles on the surface of leaves, stems, and fruit after evaporation of the water. Kaolin acts as a physical barrier preventing insects from reaching vulnerable plant tissue. It acts as a repellent by creating an unsuitable surface for feeding or egg-laying.

  Surround applications begin at Petal Fall and get reapplied weekly to maintain coverage and deter egg-laying.  

• Do not apply insecticides until bloom is completely finished to reduce unwanted pollinator exposure to insecticides.  For information on rainfast characteristics of some insecticides, see the following article in Fruit Gower’s News: http://fruitgrowersnews.com/news/rainfast-characteristics-insecticides-f...

Overview

SJS infested bark has a grey, roughened appearance due to scale insects on limbs and trunk. Infested fruit develop a reddish-purple ring surrounding each spot where a scale settles.

Biology

• Adult scales are round (females) or oval (males), about 1/16 inch in diameter, and greyish with a raised yellow nipple in the center. Immature SJS overwinter on twigs and branches under scale covering. Around Bloom, winged males emerge, seek out female scales, and mate.
• Tiny, bright yellow nymphs or "crawlers" emerge in mid-late June. Each female produces several hundred living young which disperse over the tree in search of suitable feeding sites.
• As crawlers mature they produce a whitish secretion that blackens with time and hardens into a waxy protective covering.
• Second generation male flight and mating usually begin by mid-July, producing crawlers by mid-August.

Monitoring

• Crawler emergence can be monitored using a band of black electricians' tape wrapped around an infested limb and coated with a thin layer of petroleum jelly. Tape should be inspected daily with a hand lens until active crawlers are found.
• The decision to treat is usually based on finding infested fruit at previous year's harvest. Examine 50 fruits per tree on 2 trees per acre and treat if you find more than 0.1% fruit with SJS injury.

Management

• Thorough, yearly pruning helps manage SJS.
• Established, heavy SJS populations are difficult to manage and may require both semidormant oil application and insecticide application targeting crawlers.
• For best results, apply 60-70 sec oil (3 gal/100 gal for heavy infestation, 2 gal/100 for others) around Half Inch Green.
• Apply insecticide when crawlers become visible. Some insect growth regulator insecticides have been very effective at controlling crawlers.

Overview

Spongy moth caterpillars damage fruit trees by feeding on leaves, flowers, and fruit. Generally spongy moths do not require management, but periodically, populations build up to very damaging levels.

Biology

• Spongy moths overwinter as egg masses in woods surrounding orchards and hatch in late April to early May and feed on leaves through June. Spongy moths are seen every year, but usually do not cause problems in apple orchards unless spongy moth populations are very large.
• Small caterpillars can blow into orchards from surrounding woods.
• Large caterpillars can walk into orchards from surrounding woods.
• Caterpillars pupate in early July and adult moths emerge mid - late July. Female moths deposit one egg mass containing 500-1000 eggs.

Monitoring

• Before eggs hatch, scout surrounding woods for spongy moth egg masses.
• From Tight Cluster through Bloom, scout leaves and buds for small, black spongy moth caterpillars. Young trees, in particular, should be monitored.
• Through the end of June, scout apple trees next to spongy moth infested woods for caterpillars walking into orchard.

Management

• Apply a Bt insecticide such as DiPel when caterpillars are 2nd instars, probably during Bloom.
• If large caterpillars migrate into orchards, apply insecticide effective against mature caterpillars such as Delegate or Altacor.

Overview

Several species of stink bugs feed on apples in New England, but the brown stink bug (Euschistus servus) may be the most common. Brown stink bugs look very similar to the invasive species, brown marmorated stink bug (BMSB). BMSB is already causing problems in some locations in New England. For more information on this pest, see the BMSB section of this guide. For updates, see https://www.stopbmsb.org.

Stink bugs' long piercing-sucking mouthparts make deep punctures that create corky flesh under the surface. The puncture is difficult to see, even with a hand lens. Each puncture may be surrounded by a small greenish area that is slightly sunken. This injury should not be confused with cork spot, which usually occurs around the calyx end

Biology

• In New England, stink bugs spend the winter as adults, hiding under stones, boards, ground cover, and weeds. In springtime, the adults become active. As the adults come out of their overwintering sites, they feed on the plants that are available.
• Stink bug nymphs and adults can begin feeding on apple flowers and continue through harvest. Native stink bugs tend to be late summer pests, but can be found throughout the fruiting season.
• Adult feeding during bloom can cause the fruit to abort, and feeding later in the summer can cause a deep cat-facing injury such as that caused by TPB, or depressed, dimpled, corky, or water-soaked areas on fruit skin.

Monitoring

• Examine developing fruit for stink bug damage and live insects.
• BMSB can be monitored with baited, black pyramid traps.

Management

• Eliminating broadleaf weeds, especially legumes, will contribute to managing stink bugs.
• Do not allow ground covers to grow under tree canopies.
• Many insecticides are ineffective at controlling stink bug populations. Apply effective insecticide at first signs of infestation. BMSB is a very mobile pest and may reinfest treated areas quickly. If repeat applications are necessary, rotate active ingredients to avoid promoting resistance in local populations.

Overview

TPB feeding up to tight cluster usually results in aborted fruit. Buds fed on from Tight Cluster through Bloom may be scarred. As apple develops, damage appears as deep, sunken areas, conical in shape, with associated light corky russetting. Damage is often confined to fruit calyx.

Biology

• TPB adults are 1/4 inch long, somewhat flattened and brown in color, with black, white, or yellow markings, including a clear-yellowish triangle on each wing tip.
• Adults overwinter in protected areas within and around orchards. They are first active on warm early spring days and become abundant from green tip through petal fall. Adults feed by inserting their mouthparts into developing fruit buds. Orchards with an abundance of legumes or flowering plants in the ground cover often have high TPB populations.
• TPB feeding up to Tight Cluster usually results in undeveloped buds that fail to set fruit. Buds damaged by feeding after tight cluster may survive but will be scarred. As the apple develops, damage often appears as deep, sunken areas, conical in shape, with associated light corky russetting, often confined to fruit calyx.

Monitoring

• TPB adults can be monitored using a visual, white sticky trap set at silver tip. Traps should be stapled to stakes or hung on low branches no higher than knee height near orchard perimeter. Use at least one trap per 3 acres and at least 3 traps per monitored block. Action threshold is cumulative average of 5 TPB per trap by Tight Cluster or 8 TPB by Pink.
• Examine 10 terminals per block for bleeding buds. Action threshold is 2-3 bleeding sites per 10-terminal sample.
• TPB activity is highly dependent on temperature, so that 2 or 3 days of warm (50-60 degrees), sunny weather triggers increased foraging and feeding behavior.

Management

• If needed, apply insecticide Tight Cluster to Pink bud stage. Use of synthetic pyrethroids may lead to outbreak of European red mites since these insecticides are harmful to beneficial mites.
• Control may be enhanced by spraying insecticide on a warm, sunny, calm day when TPB are most active.
• Destroying broad leaf weed hosts in and around the orchard in the fall may decrease overwintering TPB.
• Avoid mowing or using herbicide between Pink and Petal Fall because disturbance of alternate hosts in the groundcover may cause TPB to move into apple trees.

Overview

Winter moth caterpillars damage apple fruit by entering flower buds at Green Tip and then feeding on developing flower buds, destroying the flowers. Caterpillars continue feeding on opened flower clusters and leaves until late May.

Biology

• Winter moth are currently a problem to apple and pear growers in eastern Connecticut and Massachusetts, Rhode Island, and coastal Maine.
• Caterpillars hatch from overwintering eggs around McIntosh Green Tip. Caterpillars wriggle into buds without feeding.
• Once inside buds caterpillars feed, destroying flower parts. 100% of apple crop can be destroyed by these inch worms.
• Mature caterpillars (1 inch long) drop to the ground on silken threads in late May.
• Caterpillars pupate in the soil and remain there until late November when moths emerge. Male moths are light brown and attracted to lights; female moths are flightless and not easily seen.

Monitoring

• Set up tree wraps before moths emerge in November. Tree wraps encourage females to deposit eggs on tree trunks below the wrap.
• Check winter moth eggs for color change from orange to blue, indicating eggs will hatch in 1-3 days. Apply pesticide when eggs first begin to hatch. A Bt insecticide such as DiPel will not control hatching winter moth caterpillars.
• Scout flower buds at tight cluster and pink bud stages and apply inseciticide if many caterpillars are found.
• Winter moth caterpillars look identical to green pug moth caterpillars until caterpillars are half grown, then green pug moth caterpillars develop a burgundy-colored stripe. Green pug moths do not tend to build up to damaging levels.

Management

• In orchards with high populations of winter moths, apply insecticide when eggs begin to hatch, usually around McIntosh Green Tip. Bt insecticides, such as DiPel, not effective against newly hatched caterpillars.
• If egg hatch is delayed by cold weather, additional spray may be needed.
• Apply insecticide if finding many green inchworm caterpillars Tight Cluster - Pink.

Overview

• Apple scab is caused by the fungus Venturia inaequalis, which infects the leaves and fruit of apples. Scab is one of the most important diseases of apples in New England, and if left unmanaged, will cause significant damage.
• Infections start in the early spring, caused by spores from leaves infected the previous growing season that overwinter on the orchard floor or close to the orchard border. If infections start, they will produce more spores which can rapidly spread the infection during wet weather in spring and early summer.
• Management should involve both cultural and chemical control, with fungicide sprays guided by weather conditions and fungicide properties, preferably using disease forecast models and reliable weather data for the orchard site.
• Sanitation targeting apple leaves in the orchard should be done in fall or early spring to decrease scab risk.
• Resistance to fungicides is common in apple scab. Application strategies to reduce resistance risk, such as mixing different FRAC groups, including multi-site fungicides, and limiting amounts of any one FRAC group per season should be used.
• Scab-resistant cultivars have been grown commercially on a limited basis and can eliminate the need for scab fungicides, though some fungicide applications will probably be needed for other diseases.

Symptoms

Apple scab can occur on any apple tissue, but is most commonly seen on leaves and fruit. Small, raised, fuzzy, olive-colored spots will first appear on fruit cluster leaves near bloom, or on early vegetative leaves and immature fruit after petal fall. On leaves, infections may be visible on the top or undersurface. These primary lesions expand if untreated, turning yellow and eventually black. With heavy infections, the entire leaf turns yellow and drops. Leaves that are completely covered with scab are said to have “sheet scab”. Secondary lesions, formed by spores produced in the first or primary lesions, are similar to the primary lesions. They develop on vegetative leaves or fruit through the growing season. Scab infections on fruit first appear as gray to black spots that develop cracks as fruit grows. Tissue becomes brown and corky around and in infections. Multiple infections deform the fruit. In storage, fruit infected at the end of the growing season may develop small, dark spots called “pinpoint scab”.

Disease Cycle

A key to scab management is preventing primary infections early in the growing season. If primary scab is controlled, then there is no need to continue scab fungicide applications during the rest of the growing season. Primary control greatly reduces the chance that resistance to fungicides will develop, and reduces the chance of scab in the next season.

V. inaequalis overwinters in apple leaves infected the previous season that fell to the ground. Scab spores may also overwinter in bark cracks and in buds, and cause infection in the spring, but this is rare in New England. 

Warming temperatures in the spring around bud-break stimulate the fungus to make mature ascospores in old, overwintered leaves. The first mature spores are generally available at the same time trees are first producing green tissue, green tip, though the relative amount of mature spores varies. The first type of scab spores, ascospores, can cause primary infections from green tip until all ascospores for the year have matured and been released, usually one to two weeks after petal fall, though again this timing varies depending on periods of dry weather. In orchards where there were very few or no scab infections the previous year, and where sanitation is done, the risk of infection at green tip is relatively low. The most intense spore release and highest scab risk usually occurs when trees are at pink through to petal fall.

Daytime rains release mature ascospores into the air when they are mature. Those spores may land on emerging apple leaves or new fruit causing primary infections. For infection, apple tissue must be wet for a minimum number of hours, depending on temperature, so it is important to measure the length of wetting periods. Near freezing, the fungus needs two days of leaf wetness to infect, while at 61ºF to 75ºF it takes only 9 hours. After infection, it takes from 9 to 17 days from the time of infection for visible symptoms to show, again depending on temperature. See IApple Scab  Infection Periods.

Primary infections produce conidia, spores that cause secondary infections. Several additional secondary infection cycles can occur during a growing season, depending on rain, though apple tissue becomes more resistant to scab as summer progresses. In the fall, leaves drop and a new generation of ascospores develops the next spring.

Chemical Controls

Most commercial apple cultivars are susceptible to apple scab, and commercial management requires fungicide applications at approximately weekly intervals from bud break to two weeks post-bloom. However, spraying according to the calendar rather the the risk of apple scab will use more fungicide sprays than are usually necessary, so chemicals should be applied according to risk forecasts, most easily obtained using decision support systems, such as Ag-Radar or NEWA.

Detailed options for fungicide selection are given in the Apple Spray Table. The following is a general overview of chemical management of scab.

Early season - silver tip through tight-cluster. A dormant to green tip application of a copper fungicide primarily targeting fire blight is recommended, and is a spray that will also give 5 to 7 days of protection against scab. A combination of captan (3 lb. of Captan 50W or equivalent) plus an EBDC fungicide (3 lb of Dithane M45 or equivalent), a so-called “captozeb” mix, is effective in most orchards at this time. In blocks where scab pressure is high or during extended wet weather, applications should include Syllit, Vangard or Scala. Do not apply more than two applications of these materials in a season.

Tight cluster through pink. If scab pressure is low, the captan/EBDC mix is sufficient. Keep in mind, this is the time when primary scab risk is highest so do not take risks. For moderate to high risk situations, combine a multi-site fungicide, captan or EBDC, with a site-specific fungicide:

• strobilurine / QoI - Flint or Sovran;
• SDHI - Fontelis or Aprovia;
• SDHI plus QoI pre-mix - Luna Sensation, Merivon or Luna Tranquility.

Petal fall through first cover. Again, where and when scab pressure is low a captan/EBDC mix is sufficient. In higher risk situations, combine a multi-site fungicide, captan or EBDC, with a site-specific fungicide:

• DMI fungicide with high efficacy against scab - Inspire Super, Indar, Topguard, or Rally
• strobilurine / QoI - Flint or Sovran
• SDHI - Fontelis or Aprovia
• SDHI plus QoI pre-mix - Luna Sensation, Merivon or Luna Tranquility. 

There are serious problems with resistance to scab fungicides. See Resistance management: apple fungicides for details.

Damage from Scab Fungicides

Mixing captan with oil, other pesticides that contain petroleum-based carriers, or with spreader/sticker/penetrant chemicals may cause damage to fruit and foliage. For tank-mixes that contain several pesticides, thinners or nutrients, avoid using captan. Minimize or avoid use of captan from petal fall through first cover to decrease the risk of fruit damage.

Sanitation

Sanitation targets overwintered inoculum, reducing it and subsequent risk of infection and the magnitude of epidemics that may occur. Leaves on the orchard floor are swept and ground up using mowers or flail choppers in the spring before bud break. In addition, as an alternative, 5% urea may be sprayed on trees just before leaf drop in the fall, or to the orchard floor after leaves drop in fall or spring. Both chopping and a urea spray may be used for more effective control.

Resistant Varieties

Apple varieties vary in their susceptibility to apple scab, and some cultivars are resistant to scab. Cultivars such as McIntosh, Cortland, and Empire are susceptible, while Golden Delicious and related cultivars are less susceptible. Honeycrisp is somewhat resistant to apple scab. Several cultivars have single-gene resistance, for example, Liberty, Modi, Topaz, Pristine, and Ariane, though some scab strains that can infect these varieties have developed in specific areas. Using a few fungicide applications to manage other apple diseases reduces the risk that this resistance will be develop.

Biological Controls

There are an increasing number of biopesticide products that have been labelled for controlling apple scab. However, while they may work reasonably well under low inoculum conditions, they are limited in their ability to manage apple scab under high disease pressure.

Overview

• Fire bight is caused by the bacterium Erwinia amylovora. Outbreaks in New England are sporadic, but have become more common in recent years.
• Infection of blossoms occurs during warm weather in conjunction with wetting events. Bacteria then migrate through the vascular tissue to the growing shoots and rootstocks killing tissue and whole trees.
• Fire bight management is a combination of tactics applied every year.
• Sanitation is accomplished by removing blighted shoots and whole trees.
• Chemical control begins with a copper spray at silver tip to green tip. Monitor weather data and use a forecast model to determine the need for antibiotics and biopesticides at bloom.  Applications of Apogee or Kudos for shoot blight may be made during active shoot growth.

Symptoms

Fire blight symptoms can show on blossoms, fruit, leaves, shoots, branches and limbs, and rootstocks, and generally are readily recognized. 

Blossoms are often the first tissue to show fire blight symptoms. Infected flowers first have a water-soaked appearance that quickly turns black or brown. Bacteria may spread quickly, first wilting the entire blossom cluster which then turns brown or black, then spreading to adjacent leaves and shoots. Temperature drives symptom development. The warmer the temperature, the sooner symptoms appear and the faster infections spread. After wilting, the tissue may show a sticky white to yellowish ooze produced by the bacteria.

One or more weeks after petal fall, shoot blight can develop. This wilting and browning or blackening of young, vegetative shoots is a classic fire blight symptom, with the young shoot tips bending over into a hook, like the curved end of a cane. Again, if the weather is warm and humid, bacterial ooze droplets may form at the base of the shoot. Shoot blight can expand into older wood, causing dark, sunken cankers. Once in the main trunk of smaller young trees, the whole tree may rapidly wilt, turning brown or black, as if scorched. 

Fire blight cankers are a site where E. amylovora overwinter. As weather warms in the spring, the margins around cankers become less defined as bacteria move into surrounding tissue. Nearby shoots can be infected, producing a symptom called canker blight, where shoots have a characteristic yellow-orange color in the wilting tips in the early weeks after petal fall.

Rootstocks may be more susceptible to fire blight than scions. The pathogen may not cause visible damage to the scion before traveling to the rootstock, where senstive rootstocks will rapidly collapse, killing the tree. Alternatively, rootstocks may be more directly infected if root suckers are present and develop blight.

Disease Cycle

E. amylovora infects many plants in addition to apples and pears, including hawthorn, quince, mountain ash and cotoneaster. All of these plants may be a source of inoculum. The bacteria overwinter in bark and wood at the edges of cankers formed in previous growing seasons. With warm weather, around 65 F, the bacteria multiply and come to the canker surface as sticky ooze droplets. From there, they can be carried to other plants by wind-driven rain or insects.

Insects play a critical role in flower infection, when apples are most likely to become infected with fire blight. Insects deposit bacteria on stigmas in flowers, where they can multiply but typically do not cause infection unless washed to the nectary openings at the base of the flower by rain or heavy dew. Blossoms wilt and die within one to two weeks of infection, producing bacterial ooze that can infect new shoots. Insects and rain move bacteria to shoots, and they infect through microscopic wounds caused by  wind-whipping or possibly insect feeding, or large wounds caused by hail. More bacterial ooze on these shoots, inoculum that can cause new infections as long as shoots keep growing. 

E. amylovora can move systemically in plants, without producing symptoms. The bacteria are also present on non-symptomatic plant surfaces. Their growth on and in plants is driven primarily by temperature. Below 60 F there is little bacterial growth, and low populations of bacteria don't present a fire blight risk. However, at warmer temperatures in the range of 70 to 80 F, especially with high humidity, bacterial populations explode, and soon reach levels that can cause blight. When trees are in bloom, the combination of a high population of bacteria and rain or heavy dew generally lead to infection.

Management

While fire blight is a sporadic disease, when it does show up it can be devastating. Fire blight management involves several tactics at different times in the year, and should be done on an annual basis. Here is a list of tactics to use through the year.

Early Season Copper

Growers should use a dormant, or better, a silver tip/bud swell copper spray every year. Basically, copper is toxic to bacteria on the plant surface, and copper residue will reduce the population of E. amylovora in an orchard. Copper residue is largely depleted after two to three weeks, depending on rain, so does not protect flowers. There are many copper formulations. Apply a minimum of 2 lb. of metallic copper per acre.If in doubt about how much metallic copper a product contains, use the high label rate recommended at silver to green tip. Copper may be used with oil (1 qt./100 gal.), which can act as a spreader/sticker for the copper. Because copper sprays are meant to suppress the population of E. amylovora in an entire orchard, spray the whole orchard, not just the most susceptible cultivars or places where fire blight has occurred in the past.

Monitor for Fire Blight Risk at Bloom

The overwhelming majority of fire blight epidemics start at bloom, and shock waves from these primary infections will reverberate in an orchard through the summer and beyond, so it is essential that blossom blight be stopped. To do this, use a fire blight forecasting model.  There are two basic models, MaryBlyt and CougarBlight, which may be accessed and used independently, but which have also been incorporated into decision support systems linked to weather data on the web. Growers will need either an electronic weather station or a subscription to virtual weather to use these systems, but it makes monitoring much easier. Contact NEWA or Ag-Radar for details.

Spray Antibiotics at Bloom is Needed

If the fire blight forecasting system says that fire blight risk is high, then an antibiotic spray should be applied in bloom. 

Overview

• Powdery mildew is caused by the fungus Podosphaera leucotricha, which infects the terminal leaves and developing buds of new shoots.
• Infection begins with overwintering fungus in apple terminal buds. In the spring, infected shoots with shriveled leaves emerge from these buds covered with white, powdery spores, which can cause new infections.
• Cultural control is best achieved by avoiding cultivars that are highly susceptible to powdery mildew, such as Cortland, Idared, Gingergold, and Jonathan. 
• Chemical control targeting powdery mildew should be used only in blocks with a history of the disease. Use fungicides that also control apple scab, making sprays at weekly intervals from tight cluster to terminal bud set.

Symptoms and Signs

Primary infections show as poorly growing shoots with whitish, shriveled leaves that are covered with powdery spores. Spores from these shoots cause new infections on terminal leaves.  These first appear as pale yellow infected areas that then produce new spores. Infected leaves curl up, and become covered with a grayish to white fungal growth. These new spores cause additional infections on developing fruit. Fruit infections lead to a webbed russeting, making fruit much less valuable in the market.

Disease Cycle

Unlike most fungal diseases, powdery mildew is worse in warm, dry weather. Regions with cool, wet summers rarely have significant apple powdery mildew problems.

Podosphaera leucotricha overwinters in terminal buds of shoots infected the previous year. These  infections become visible around tight cluster. Spores produced on infected shoots cause secondary infections on leaves and buds, and eventually on developing flowers and fruit. Secondary infections generally appear near petal fall. Infected flowers do not develop normally and produce no fruit. If mildew isn't treated and allowed to grow, it will cover shoots and leaves, and grow into terminal buds where it overwinters. Once growth stops in mid-summer, new infections stop. If powdery mildew inoculum is in an orchard when the fruit cuticle is developing, fruit finish can be damaged showing as a webbed russett on fruit by harvest.

Winter temperatures below 10°F kill some of the over-wintering mildew in buds, and temperatures of –10°F will eliminate 95% of over-wintering mildew. Therefore, powdery mildew is often worse following mild winters, particularly when weather between bloom and petal fall is dry and warm. 

Chemical Control

In New England, spray applications specifically targetting powdery mildew usually are not generally necessary, though warm, dry springs can lead to increased infection of susceptible varieties. For those varieties, in blocks with a history of powdery mildew, scab managment fungicides used from pink through second cover should also have activity against powdery mildew. During extended dry, warm weather during this period, specific applications for mildew may be needed, even when scab fungicide sprays are not.

The most common multi-site fungicides, captan and mancozeb, are ineffective against powdery mildew. DMI fungicides vary in effectiveness. Unfortunately, the DMIs most effective against powdery mildew, Rhyme, Rally, Rubigan and Procure, are least effective against scab, and vice-versa. QoI fungicides, Flint, Flint Extra and Sovran (and pre-mixes with Group 11 ingredients) have good efficacy against powdery mildew. SDHI fungicides, Aprovia, Fontelis and Sercadis (and pre-mixes with Group 7 ingredients) are somewhat less effective, but still provide good control.

Low rates of sulfur are effective in low disease pressure environments, such as New England, but the risk of sulfur injury increases as temperatures go over 85°F. In organic production systems, sulfur applied at weekly intervals, and bicarbonate and peroxide-based fungicides applied on 3-5 days intervals are the best options.

Cultivar Resistance

Apple cultivars differ how susceptible they are to powdery mildew. Cortland, Gala, Ginger Gold,  Idared, Jonathan, Mutsu (Crispin), Paulared, and Rome are all highly susceptible, while Empire, and Fuji are much more resistant.  McIntosh and Golden Delicious can develop significant mildew when they are next to highly-susceptible cultivars that have significant infection.

Overview

Cedar-apple rust is a fungal disease that requires both a Rosaceaous host (such as apple) and a cedar host (such as Eastern red cedar). On apples, bright orange-yellow lesions are first visible after bloom. These lesions develop from spores released from galls on cedars earlier in the spring. Some species of cedar-apple rusts also produce lesions on fruit.

Disease cycle

During prolonged wet periods in the spring, typically from late April to late May in southern New England, galls on cedar/junipers secrete orange-brown gelatinous tendrils (known as telial “horns”) which produce spores. Spores blow from galls and those that land on apple leaves can cause infections if leaves remains wet for 4–6 hours.

Lesions on apple leaves become visible soon after bloom, but continue to enlarge and become more striking in July and August. In late summer, spores are produced on the underside of apple leaves and spread the disease back to cedars.

Management

Fungicides are needed to protect leaves and fruit of susceptible varieties during periods of extended wet weather from pink through 2nd cover. At this time there are no effective organic fungicides that adequately manage cedar-apple rust.

Apple cultivars with resistance to cedar-apple rust include: Baldwin, Delicious (red), Empire, Enterprise, Gala Suprene, Jerseymac, Keepsake, Liberty, McIntosh, Milton, Niagara, Paulared, Redfree, Regent, Sansa, Spartan, Sundance, Viking, and Zestar!.

Apple cultivars that are very susceptible to cedar-apple rust include: Ambrosia, Braeburn, Cameo, Chinook, Crimson Crisp, Fuji, Gala, Ginger Gold, Golden Delicious, Jonathan, Lodi, Prima, Rome Beauty, Shizuka, Spigold, Twenty Ounce, Wealthy, Winter Banana, and York Imperial.

Overview

• Sooty blotch and flyspeck (SBFS) are, for practical and management purposes, one disease that blemishes the surface of apple fruit, though several fungi may cause the disease.
• Initial infections start from spores produced primarily from wild plants along orchard borders, particularly trees and shrubs.
• Disease activity. The disease is most active from one to two weeks after petal fall through to harvest.
• Cultural controls such as pruning, mowing and removing plants on orchard borders or planting as far as is practical from woodland and other sources of inoculum decrease SBFS risk.
• Fungicides are the primary control for SBFS. The initial fungicide application each season can be timed using accumulated leaf wetness hours from petal fall. Later fungicide applications should be timed according the amount of rain or the time that has elapsed since the previous application.

Symptoms and Signs

Sooty blotch appears as dark, irregularly shaped areas, like charcoal smudges on fruit. Flyspeck develops distinct black, pinhead-sized spots, generally clustered in groups of 10 to 50. These signs are fungal growth on the surface of apples, not technically symptoms. They often appear together on fruit, but one or the other may occur alone. Details concerning the signs, such as speck size or blotch margins may vary significantly, as many different fungi can cause SBFS. Other than causing cosmetic damage, and rarely some dehydration to fruit in storage, SBFS is not technically a disease, as it does no real harm to apples. However, significant blemishing causes fruit to be downgraded.

Disease Cycle

The different life cycles for the many fungi that may contribute to the SBFS disease complex are not well understood. Different species of fungi predominate in different apple production regions, but all have life cycles that are similar enough that symptom development can be reasonably well predicted and a single management approach used. Infection by SBFS fungi occurs soon after fruit set, though symptoms may take several weeks to show, depending on weather. Disease development is dependent on high levels of humidity in the tree canopy. Extended wet weather or periods of high humidity enable SBFS fungi to colonize apples and grow, but they grow slowly if at all during dry periods. New infections can occur throughout the summer to harvest. The fungi may remain invisible for several weeks, first appearing in late summer or early fall. Some SBFS fungi apparently have secondary spore production and infection cycles related to rain and high humidity, with higher rates of disease occurring in years with heavy or frequent rain. These fungi appear to overwinter on plants adjacent to apple orchards.

Chemical Control

Fungicides applied approximately every two to three weeks, starting with second cover, will generally control SBFS. Accumulated leaf wetness hours from fruit set (170 to 220 h) can be used to more accurately time the first SBFS fungicide application. After that, timing should be based on the amount of rain and the time from the previous fungicide application. The most effective fungicides against SBFS include the strobilurins, Flint, Sovran, Pristine, and thiophanate-methyl, Topsin, T-Methyl. Captan is not as effective, but provides good control, and is a useful multi-site fungicide to mix with the more effective single-site materials for resistance management. Inspire Super and other pre-mixes that contain a QoI (Luna Sensation, Merivon) also provide good control.

Fungicides should be re-applied when they are depleted, either by rain or breakdown over time. Use the following depletion rules, applying whichever comes first.

• Pristine (14.5 oz/A) – 2.5 inches rain or 21 days
• Flint (2.5 oz/A), Sovran (6.4 oz/A), or thiophanate methyl (0.8 lb/A or 20 fl. oz/A) PLUS captan ( 2.5 lb/A Captan 80 or equivalent rate for other formulations) – 2.0 inches of rain or 21 days
• Captan (4 lb/A Captan 80 or equivalent rate for other formulations) – 1.5 inches of rain or 14 days 

Alternative Chemicals. Sulfur, liquid lime sulfur and phosphorous acid compounds (for example Prophyte, Phostrol) also suppress SBFS, though less is known about their depletion rates. With liquid lime sulfur there is risk of russeting on fruit and foliar stress.

SBFS blemishes may be removed or significantly reduced using postharvest fruit dip treatments in low-concentration chlorine bleach solutions (500 to 800 ppm chlorine) followed by brushing on a commercial grading line. 

Non-Chemical Controls

Cultural Control

Anything that slows drying in apple tree canopies encourages SBFS development. So larger trees that are poorly pruned develop more disease. Similarly, trees in areas where air circulation is poor develop more disease. The source of many of the SBFS fungi is wild plant hosts in woods or hedgerows adjacent to orchards. Cutting back these border plants, particularly well-known hosts such as wild blackberries, reduces disease pressure. Keep grass in the orchard mowed to reduce humidity in tree canopies.

Resistant Varieties

Apple cultivars vary in the amount of SBFS at harvest, but this is primarily related to harvest date rather than resistance pathogen colonization. Later harvested cultivars have the highest SBFS incidence. Lower SBFS incidence on the earlier maturing cultivars apparently results from disease avoidance, as these apples are exposed to fewer hours of wetting and high relative humidity, environmental factors favorable for growth of SBFS fungi.

Overview

The white rot fungus, Botryosphaeria dothidea, often referred to as “Bot rot” or Botryosphaeria rot, can be a distinct canker on twigs, limbs, and trunks. The fungus produces two types of fruit rot, but leaf infections do not occur. Drought stress and winter injury have been associated with an increase in infection and canker expansion. This is a relatively weak fungal pathogen and is only problematic when a tree is stressed, such as due to drought, winter injury, insect damage, or fire blight.

The black rot and frogeye leaf spot fungus, Botryosphaeria obtusa, attacks fruit, leaves, and bark of apple trees and other pomaceous plants.

Symptoms of white rot

New infections on twigs and limbs start to become evident by early summer, appearing as small circular spots or blisters. As the lesions expand, the area becomes slightly depressed.

Cankers stop enlarging in late fall and can be indistinguishable from black rot canker, making isolation of the pathogen necessary for correct identification of the causal organism. By spring small, black pycnidia (the spore-containing structures of the fungus), appear on the smooth surface of new cankers. On older cankers, these may be present throughout the year. Cankers exhibit a scaly, papery outer bark that is often orange and that can easily be peeled off of the tree. Tissues beneath the canker surfaces are watery or slimy and brown. Most cankers are not deep, extending at most to the wood.

Fruit rot infection results in two types of symptoms, depending on the developmental stage of the fruit. One type originates from external infections and the other appears to start internally. External rot is first visible as small, slightly sunken, brown spots that may be surrounded by a red halo. As the decayed area expands, the core becomes rotten and eventually the entire fruit. Red-skinned apple varieties may bleach during the decay process and become a light brown. Because of this characteristic, the disease may be referred to as "white rot."

Symptoms of black rot

The first signs of black rot are small, purple spots appearing on the upper surfaces of leaves and enlarging into circles 1∕8 to ¼ inch in diameter. Leaf margins remain purple, while the centers turn brown, tan, or yellowish brown, giving the lesions a "frogeye" appearance. Small, black pycnidia (pimplelike fruiting bodies of the fungus) may appear in lesion centers.

Infected areas of branches and limbs are reddish brown and are sunken slightly below the level of surrounding healthy bark. These cankers may expand each year, a few eventually reaching several feet in length. The margins of older cankers are slightly raised and lobed, and the bark within their centers usually turns light-colored, loosens, and scales off raggedly. This characteristic is not confined to black rot cankers, so it is not a good diagnostic symptom. Pycnidia form on dead wood of the cankered areas.

Fruit rot usually appears at the calyx end of the fruit. It can originate at any wound that penetrates the epidermis, including insect injuries. There is usually one spot per fruit, a characteristic that distinguishes black rot from bitter rot. Initially, the infected area becomes brown and may not change in color as it increases in size, or it may turn black. As the rotted area increases, often a series of concentric bands form, darker bands of mahogany brown to black alternating with brown bands. The flesh of the decayed area remains firm and leathery. Eventually, the apple completely decays, dries, and shrivels into a mummy. Pycnidia containing spores of the black rot fungus appear on the surface of rotted tissue.

Disease Cycle for white rot

White rot overwinters in fruiting bodies on dead, woody tissue. During spring and summer rains, spores ooze from these structures and are splashed to other parts of the tree. Dead wood and fire-blighted twigs and branches are especially susceptible to invasion, but living twigs, branches, and trunks may also be attacked. Fruit infections can occur at any time from the bloom period to harvest. Infections in young apples usually are not evident until the apples are nearly mature. External rot lesions are found most commonly on the sides of fruit exposed to high temperatures. Drought, heat stress, mechanical wounding, and winter injury favor disease development. The fungus grows best under warm conditions, with the optimum temperature for infection about 86°F.

Disease Cycle for black rot

Black rot can infect from petal fall through harvest. The fungus overwinters in fruiting bodies (pycnidia and perithecia) on dead bark, dead twigs, and mummified fruit. It can invade almost any dead, woody tissue and is frequently found in tissue killed by fire blight. Early leaf infections often are visible as a cone-shaped area on the tree, with a dead twig or mummified fruit at the apex.

In the spring, black pycnidia and perithecia release conidia and ascospores, respectively. Conidia may continue to be produced during wet periods throughout the summer and may remain viable for long periods. When wet, the pycnidium produces a gelatinous coil containing thousands of spores. Disseminated by splashing rains, wind, and insects these spores can infect leaves, the calyxes of blossoms, tiny fruit, and wounds in twigs and limbs. Leaf infection develops during petal fall, at which time conidia attach, germinate in a film of moisture within 5 to 6 hours, and penetrate through stomata or wounds. The optimum temperature for infection is about 68°F. Infections of fruit and wood may not become visible for several weeks.

Initial fruit infections occur during the bloom period but are not usually apparent until midsummer as the apple approaches maturity. Throughout the growing season, infections occur through wounds. Harvest injuries may become infected and the fruit may decay during or after storage, especially if the fruit was harvested during a wet period. Dead fruit spurs or twigs, particularly those killed by fire blight, pruning wounds, winter injuries, and sun scald, are commonly invaded by the black rot fungus.

Management for both diseases

Since stress predisposes apple trees to white rot and black rot, take measures to minimize stressors, such as water stress, winter injury, disease, and insect damage.

Management programs based on sanitation to reduce inoculum levels in the orchard are the primary means of control. Prune out cankers, dead branches, twigs, etc. which serve as inoculum sources and dispose of dead wood. This should be an important component of both current-season and long-range management. Prune and remove cankers at least 15 inches below the basal end; properly dispose of prunings by burial or burning.

Remove mummified fruit of black rot if practical. Cortland apples are especially prone to forming black rot mummies.

Captan + Topsin M and fungicides containing a strobilurin (FRAC Group 11 Fungicides) as an active ingredient are effective at managing white rot and black rot on fruit. Merivon provides excellent control of summer diseases such as white rot, black rot, bitter rot, fly speck and sooty blotch. Note: sterol inhibitor fungicides, such as Indar, Rally, Topguard, have no activity against black rot.

Overview

• Bitter rot of apple is more common in the warm, humid climate of the southeatern U.S., and occurs sporadically in the Northeast. Extensive damage can develop rapidly in New England orchards during periods of prolonged hot, wet weather if inoculum sources are present.
• Bitter rot caused by fungi in the same genus, Colletotrichum, with many different species shown to infect apple fruit. 
• Colletotrichum spp. infect during extended warm rainy periods after fruit set, continuing through the summer. Infection risk increases as fruit matures.
• Bitter rot is more common on light or bicolored fruit such as Empire, Honeycrisp, Mclntosh, Sunrise, Paulared and Jonagold.

Symptoms

Typically apples first show bitter rot symptoms in July and August, and fruit susceptibility increases as it matures. Humidity, and the presence of sources of inoculumare also factors that determine when the disease first appears. Bitter rot spots usually appear on the side of the apple directly exposed to the sun. Early fruit lesions are brown, slightly sunken spots. If the apple is cut open, the rotted area beneath the lesion is V-shaped in cross-section. Bitter rot lesions expand most rapidly at a temperature of 86^oF. As lesions expand they remain light to dark brown and flattened, developing concentric, target-like rings of spores, colored pink, slight orange to light tan. Severely infected fruit become shriveled and persist on the tree as mummies, a source of inoculum.

Disease Cycle

The disease cycle of the bitter rot fungi related to apple fruit infection is only partially understood. Bitter rot fungi overwinter in dead wood or mummified fruit in apple trees, and may live on other plants, including trees surrounding orchards or broad-leaf weeds in orchards. The fungi produce spores in spring and summer, which are released by rain and dispersed throughout trees. The optimum temperature for spore germination is 79 to 80 F, when it takes only 5 hours to infect. Infections commonly start during prolonged warm, wet weather. As soon as infected fruit produce spores, these can cause new infections. Another source of inoculum is shoots killed by fire blight which become colonized by bitter rot fungi in the same year. 

Chemical Control

Fungicide applications targeting bitter rot should start at fruit set if weather and previous disease history favor infection at that time. For the rest of the summer in orchards with a history of the disease, fungicides to manage bitter rot should be applied when prolonged warm, wet weather is predicted, particularly as fruit matures.  Among the most effective fungicides against bitter rot are the EBDCs. Unfortunately they have a 77 day pre-harvest limit. Captan and Ziram are also effective, as are Pristine and Merivon, group 7 + 11 pre-mixed fungicides. For resistance management and improved efficacy, Pristine or Merivon should be tank-mixed with captan at one half the full rate. No more than 4 applications of Pristine or Merivon should be made per year. Note: Topsin M has no effect on bitter rot.

Cultural Control

The most important cultural control is to remove sources of inoculum: dead wood, branches and shoots with cankers and fruit mummies. Following fire blight outbreaks, dead shoots should be removed as soon as practical as these can become infected with bitter rot and become inoculum sources. While yet unproven, a few other cultural methods may help control bitter rot. It may also be useful to avoid or minimize stress, particularly drought and heat stress. Some tree species close to orchards may support Colletotrichum spp., making it worthwhile to establish open buffer spaces between trees and orchard borders. Removing leaves, dead twigs and fruit mummies on the ground may reduce inoculum. Finally, removing broad-leaf weeds in the orchard may remove another source of inoculum.

Fruit thinning is an essential practice for producing commercial quality fruit and for getting consistent yield from year to year.  It increases the overall value of fruit because the reduction in crop load increases the size of fruit that remain.  For some varieties, there is an improvement in red color, as well. 

 Apple trees are prone to biennial bearing or the condition in which trees produce abundantly one year and poorly the next.  Chemical thinning in one season will increase the amount of bloom in the following season (return or repeat bloom).  Hand thinning is not as effective as chemical thinning for promoting return bloom.

The chemicals and concentrations a grower chooses, the timing of their application, and the environmental factors encountered before, during, and after application all influence the ultimate thinning response. This section of the Guide will discuss the chemicals most frequently used, the circumstances when they are used and the precautions associated with their use. Also discussed will be the timing of the applications and the environmental factors one must be mindful of when applying chemical thinners.

Thinning Chemicals

Blossom thinners

12 mm is equivalent to ½ inch

Some of the first attempts to thin involve using caustic chemicals to prevent pollination, pollen germination or pollen tube growth. Many of these caustic chemicals can cause phytotoxicity to the leaves and russeting of the fruit. If poor pollination occurs during bloom, thinning should be postponed until early fruit set. 

Lime sulfur, lime sulfur plus oil or ammonium thoiosulfate are mild blossom thinners.  Although none of these have label approval for thinning they may be applied legally on apples for other reasons. 

While less frequently used, hormone sprays can thin when applied at bloom. A bloom spray of NAA and NAAm can reduce fruit set, but are generally not applied commercially during bloom because of grower uncertainty about the extent of initial set and the desire to assess initial set before attempting to adjust crop load. Further, the most effective time to apply NAA as a chemical thinner is when fruit diameter is 7 to 12 mm.

Ethephon may also thin when applied at bloom or even several days earlier, at the balloon stage or red stage. The response appears to be quite cultivar and temperature sensitive. The use of ethephon as a blossom thinner has not been widely adopted except in locations where chemical thinning with other compounds is difficult and satisfactory results using other thinners is generally inadequate.

Postbloom thinners

The majority of chemical thinning is done with postbloom thinners. There is a comfort level for growers to delay thinner application until they know the extent of bee activity and pollination.

Naphthaleneacetic acid (NAA). It is probably the most potent of the general-use thinners on the market today, and it is the preferred material for cultivars that are difficult to thin. Its thinning effectiveness is concentration dependent. Lower concentration may cause only modest thinning while higher concentrations may overthin and reduce fruit size or not increase fruit size even though the crop load is substantially reduced. Over application of NAA may also lead to pygmy fruit formation and severe leaf epinasty on some varieties. Therefore, NAA is often combined with another thinner, especially carbaryl, and used at lower and “safer” rates. The thinning action of NAA is sometimes not immediately apparent since fruit abscission following NAA application if often delayed by as much as one or two weeks relative to untreated trees.

Naphthaleneacetamide (NAAm, NAD). NAD is a useful thinner that is frequently applied as a petal-fall spray. It is considered safer to use than NAA and it does not cause as severe leaf epinasty following application that is often experienced with NAA. NAD should be avoided on 'Delicious' since it may result in a high percentage of pygmy fruit that persist to harvest. NAD can be combined with carbaryl in situations were more aggressive thinning is desired.

Carbaryl.  Carbaryl is the most versatile thinner in general use. It is a mild thinner, and since the thinning is not rate responsive, overthinning is rarely observed. It can be used effectively over a wide range of developmental stages from petal fall until fruit grow to 18 mm in diameter. It is very toxic to bees so practically speaking the earliest time of application is at petal fall after the bees have been removed from the orchard. The Sevin XLR Plus formulation may be less of a problem near bloom since the particle size is less like pollen thus it is less likely to be transported by bees back to the hive. One of the most important characteristics of carbaryl is that it can break up fruit clusters. Carbaryl is an insecticide rather than a hormone so it is applied at higher concentrations than other postbloom thinners. 

Benzyladenine (BA). BA is a mild thinner when used by itself, but when combined with carbaryl it is a potent thinner combination that can overthin. The combination of BA with NAA for use on 'Delicious' and 'Fuji' is not recommended since pygmy fruit may form in some circumstances. Unlike other thinners, BA can increase fruit size beyond that attributed to a reduction in crop load.

Protone® (S-Abscisic Acid, ABA). ABA is a naturally occurring compound that plays a critical role in regulation of several physiological processes in a plant, especially those related to stress. If a plant is stressed or if it is sprayed with ABA stomata close, resulting in a significant reduction in photosynthesis. This in turn results in a carbon deficit in the plant. In the case with pome fruit, this happens for a long enough period during the time when developing fruit are competing for photosynthate (7-15 mm) fruit abscission will be initiated. Special attention should be paid to the weather conditions that occur especially the three days following application. If the weather is cloudy and or the temperatures are warm to hot, thinning will be favored because these conditions will increase the carbon deficit within the tree. Protone® is OMRI organic certified.

• Apples. Label recommendations for the use of Protone® on apples include using 1 to 2 applications from 5-12 mm fruit size. Starting out I would recommend using mid- concentration rates at the 10-12 mm stage.  A good nonionic surfactant is recommended for use with this product. In the past we used Regulaid with ABA with good success. This may be used with MaxCel (not NAA) for added thinning.  Protone® may cause some leaf yellowing and leaf abscission. The severity of this is  cultivar dependent. A small amount of 6-BA (MaxCel) may help reduce leaf yellowing and abscission.
• Pears. Protone® is cleared for use on pears for thinning. Pears are more sensitive to ABA than are apples. Everything being equal, a greater thinning response may be expected when used on pears. Some leaf abscission and leaf yellowing when used on pear can be seen. Based upon experience with Bartlett pears, 6-BA (MaxCel) was unable to reverse this yellowing and leaf abscission effect when used in conjunction with Protone®.

Accede® Plant Growth Regulator contains ACC, a natural compound responsible for the biosynthesis of ethylene production in tree fruits. For apple growers, it extends the thinning window beyond what is currently available, giving growers a new tool for late thinning. Accede is applied at 23 to 46 fluid ounces 100 gallons of water per acre from full bloom to when king fruit size is 15 mm (one inch) in diameter. Accede is most active when the king fruit is 15-20 mm in diameter. Do not apply Accede when frost is expected. Use of a non-ionic surfactant with Accede will improve performance and response. Accede label here...

Ethephon.  Ethephon can be used as a postbloom thinner in situations where other chemical thinners are less effective or have undesirable side effects. Ethephon has a reputation for being an erratic thinner. Part of this can be attributed to a dramatic increase in thinning response with increasing temperature following application. Also, bloom and fruit susceptibility to ethephon varies depending upon the stage of development. Ethepon is an effective blossom thinner but application made just 7 days later appears to be much less effective. Fruit redevelop thinning sensitivity to ethephon at diameters between 16 and 22 mm. Since larger fruit are sensitive to ethephon, unlike most other chemical thinners, ethephon may have a place in a normal chemical thinning program as a "last chance" thinner where other thinners do not work or where a grower made a miscalculation early in the season, and failed to apply a thinner at the normal time.   

Timing Thinner Application

The weather following thinner application is probably the single most important factor influencing thinner efficacy. The weather can not be regulated, and an accurate forecast of the weather may not extend beyond 2 or 3 days. Increasingly, growers in the eastern part of the United States make two or more thinner applications over the thinning period. This is a good strategy since it spreads thinning out over time, and increases the possibility that thinner application will coincide with favorable thinning weather. It also tends to be safer since less aggressive thinning treatments are generally used, and the chance of overthinning is reduced.

Before application. Cool, cloudy, wet periods preceding thinner application generally mean that thinning will be easier. Part of this is attributed to altered epicuticular wax and cuticle development on leaves which predisposes leaves to absorb more thinning chemical.  These conditions during and immediately after bloom may also lead to less vigorous fruit set, characterized by fruit that are not growing vigorously and have few seeds, increased seed abortion, and reduced carbohydrate reserves. Regardless of thinner absorption, these fruit will be easier to thin. Frost injury to spur leaves also will make fruit easier to thin. NAA penetration is greater into frost injured leaves and the markedly distorted spur leaves undoubtedly have a reduced photosynthetic capacity.

The two most important environmental factors that influence foliar penetration of a chemical thinner are temperature and drying time. Warm temperatures enhance uptake of NAA by apple leaves. The longer the drying time of a thinning spray the greater the penetration into the leaf. In foliar penetration studies it has been reported that the penetration of NAD increased steadily over time as long as the spray droplet was prevented from drying. During the drying process uptake into the leaf was accelerated, presumably due to the concentration effect caused by the drying. Once the droplet dried, little additional penetration occurred. Therefore, the longer the time before droplet drying, the greater chemical uptake by foliage and fruit.

Temperature following thinner application is the dominant factor influencing the response to a chemical thinner.  Elevated temperatures provides the stress required for thinners to work. Warm temperatures intensify competition among competing sinks at a time when metabolic demand is highest in the tree. If cool weather follows thinner application, thinning results are frequently disappointing. It is often better to wait 2 or 3 days until warm temperatures are forecast to occur after application than to apply a thinner when cool conditions (< 65 °F) prevail immediately after application. However, temperatures above 85 °F can lead to excessive thinning. 

Several days of cloudy weather during the bloom period where incoming solar radiation is reduced to 10% to 15% of full sun can  can intensify fruit abscission.  Applying chemical thinning sprays at the beginning of a cloudy period probably will enhance thinning. Therefore, it may be advisable to delay thinner application under circumstances where trees may be exposed to several days of cloudy, warm weather to avoid overthinning. One or two days of sun following shading partially reversed the abscission-promoting effect of shading.

Orchardists generally try to apply thinners well in advance of rain, but occasionally this cannot be avoided.  A good rule-of-thumb is if a chemical thinner dries on the leaf prior to the onset of rain, one can anticipate getting at least 80% of the thinning effect.

For more information on branching youg trees, see the UMass Fact Sheet F-140 Branching Young Apple Trees with Plant Growth Regulators

Always look at the label before making application of any PGR’s as there are further use directions and warnings on the label which may not be included here.

ReTain® (Valent USA) - For increasing fruit set of apple, cherry, European pear. APPLE: Apply one pouch of ReTain per acre, as a single application from pink stage to full bloom. Applications made prior to pink stage or after full bloom will significantly reduce efficacy of the treatment. Do not apply after petal fall. CHERRY: Apply one to two pouches of ReTain per acre during bloom. Retain may be applied as a single application of up to two pouches, or as sequential applications of one pouch per application. Applications between popcorn stage (balloon stage) to first bloom are more effective than earlier or later applications. Do not apply after petal fall. EUROPEAN PEAR: Apply one pouch of ReTain per acre, as a single application from white bud stage to full bloom. Applications made prior to white bud stage or after full bloom will significantly reduce efficacy of the treatment. Do not apply after petal fall. Can also be applied to European pear at 10 mm fruit size at a rate of one pouch of ReTain at 10 mm fruit size to increase fruit set.

Promalin® (Valent USA) and Perlan® (Fine Americas) to increase fruit set in APPLE following frost by stimulating the development of parthenocarpic fruit. Make a single application at a rate of 1-2 pints in 50-200 gallons of water per acre prior to or within 24 hours following a frost or freeze event, when the majority of the crop is between early bloom and full bloom. Do not apply to frozen foliage, blossoms or developing fruit, allow trees to completely thaw prior to application. Do not use a surfactant. Do not apply more than 2 times for this use.

Promalin® or  Maxcel ® (Valent USA) and Perlan® or Exilis 9.5SC (Fine Americas), latex paint application FOR INCREASING BRANCHING AND FEATHERING OF NON-BEARING APPLE, PEAR AND CHERRY TREES. Such an application improves tree structure by improving branch angles and increasing bud break and shoot growth in nursery stock and young trees. At the location where branching is desired, apply a uniform application in latex paint mix at a rate of 5,000-7,500 ppm (0.8-1.2 fl. oz./pint of latex paint). The latex paint mix should be applied using a brush or sponge to achieve thorough coverage of the bark surface. Application should only be made to one year old wood in the spring once terminal buds begin to swell but before shoots emerge. Applications made following shoot emergence may result in injury to the young shoots. DO NOT apply latex paint mix after bud break. Doing so may cause injury to shoot tips and reduce the effectiveness of the application for shoot growth. One-year pre-harvest interval. See F-140 Branching Young Apple Trees with Plant Growth Regulators

Protone® is registered as a defoliant to stimulate leaf drop in the fall. It may be used on nursery trees or on trees in the orchard carrying green leaves into the fall. A good nonionic surfactant should be used with this and at a rate between 250 and 1000 ppm. (16.5 - 66.1 ounces per acre.) Application on trees in the orchard is meant to speed leaf abscission and speed the development of dormancy. (May be particularly handy on non-cropping younger trees still actively growing later into the fall.)

Arrange^TM (Fine Americas, Inc.) can be applied to apple orchards in the "off" year to inhibit flower bud formation and flowering the following year. This can help break the biennial bearing cycle in apples such as Honeycrisp and Fuji (among others). The application rate is 100 to 200 ppm from petal fall to 15 mm fruit size. The Arrange label has very specific use recommendations. In 2023 the Arrange label was updated to include the higher application rate (200 ppm) to bearing orchards, and also for use on nursery apple trees to inhibit flower bud formation and promote branching. For Nursery trees make 3-4 applications of 400-600ppm (4-6 gallons per 100 gallons of water) on a 28-day interval to trees that have at least 28-30 inches of growth. For young trees (young plantings not yet bearing), begin applications during petal fall timing. Up to 4 applications may be made during the growing season of 400-600ppm (4-6 gallons per 100 gallons of water) on a 28-day interval. Again, consult the label for more specific application recommendations.

There are three options for using plant growth regulators for pre-harvest drop control. One is NAA, sold as several different products, another is AVG, sold as ReTain (Valent USA Agricultural Products), and the third is 1-methylcylopropene sold as Harvista^TM (Agrofresh). The three differ in mode of action and timing of application. NAA is typically applied just once before the onset of fruit drop and lasts for about one week before its effect is gone. ReTain is typically applied 2-3 weeks before anticipated harvest, has long lasting drop control if applied under favorable conditions, and repeat applications can be made to extend the period of time apples will remain on the tree. Harvista can be applied 3 to 21 days before harvest and requires specialized equipment (contact Agrofresh).  Both ReTain and Harvista will slow fruit ripening.  For an excellent summary/discussion of uisng apple PGR's for drop control, see this Penn State University article: Apple PGRs - Prevention of Preharvest Drop in Apple Orchards.

Application details for NAA (Fruitone-L, Refine 3.5 WSG, Refine 3.5L)

• rates of 10 ppm are usually effective, however, up to 20 ppm can be used
• good coverage at dilute application is preferred
• apply just as apples starts to loosen; apply too early and drop control will be limited; apply too late, and drop will have already started
• drop control can last for 7-10 days; sometimes two applications (at 5-7 days apart) can extend that to 14 days
• NAA application can result in accelerated fruit maturity and fruit softening

For more information: Getting the most out of that "old" stop drop: NAA (http://healthyfruit.info/hf090517ved818.html#h)

Application details for ReTain

!Note that the ReTain label gives very specific instructions depending on intended use -- read it!

General use guidelines for ReTain include:

• apply 21 to 7 days before anticipated harvest (7 day PHI)
• use one pouch (or less) per application; two applications/two pouches are allowed
• on Honeycrisp and Gala, consider using reduced rates -- early application of ReTain can inhibit color development on these varieties
• use an organosilicone surfactant at a concentration of 0.05 to 0.1% (6.4 to 12.8 oz surfactant per 100 gallons water) with ReTain, do not apply when temperature exceeds 85 degrees F.
• dilute applications are recommended, up to 2 X concentration
• avoid application when rain is expected within 12 hours
• do not apply to stressed trees

For more information: Double Applications of ReTain® to provide longer fruit drop control compared to the standard single application ReTain 

Application details for Harvista^TM

• applied at a rate of 48 to 242 fl. oz.
• Do not add any water to the container 
• Do not allow product to contact any copper
• drop control can last for 7-10 days
•  

Varieties with a strong tendency for biennial bearing may have insufficient bloom in the 'off' year and consequent low yield.  Ethephon and NAA products can be applied at lose doses in summer for a modest increase in return bloom.  Apply these in the 'on' year in four weekly (or every two weeks) applications beginning six to eight weeks after petal fall.  These compounds can hasten ripening in summer apples. 

Vegetative growth control can be achieved by application(s) of Apogee or Kudos 27.5 WDG, both containing the active ingredient prohexadione-calcium. In addition to providing growth control, early application can suppress fire blight of shoots. 

Application details for Apogee or Kudos 27.5 WDG on apples

• Apply beginning at late bloom to early petal fall; earlier applications seem to give better results (Ed. note: in 2019, Kudos was approved for use beginning at pink bud stage @ 6 oz. per acre. This application in particular may help suppress fire blight and result in improved growth control, although follow-up applications may still be necessary. Only the Kudos formulation of prohexadione-calcium has the specific pink timing recommendation. The Apogee label still says application beginning at 1-3 inches of shoot growth.)
• Apply at rates of 3 to 12 oz. per 100 gallons of dilute spray water depending on the amount of growth control desired and number of anticipated applications
• Repeat applications at 1 to 4 week intervals may be necessary for season-long growth control
• Do not apply more than 48 oz per acre within any 21-day interval, and there is a maximum of 99 oz per acre per season 
• Always use a water conditioner such as ammonium sulfate, Choice, or Quest.
• Do not tank mix with sprays containing calcium
• Chemical thinning efficacy may be decreased when using prohexadione-calcium
• Direct spray to top of trees if only vigor control is desired in the top of the tree
• Not recommended for use on Empire, may cause russetting

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