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.

​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

GPA adults and nymphs do the damage in three ways: first, they feed directly on young tender plant tissues, often drying out shoots, causing wilts and distortions; second, they produce honeydew which falls onto foliage and becomes blackened by sooty mold fungi; and third, they spread many types of viruses. Plants injured by GPA feeding will have leaves that appear curled, distorted and discolored. 

The GPA mainly attacks peach; however, apricot, plum, cherry, and a wide variety of vegetable and floricultural crops can be attached by GPA.

Eggs – oval, shiny black; about half the size of a pencil point. The eggs are only found on the bark of fruit trees.

Nymphs – Green peach aphid nymphs resemble wingless adults in color (have black legs and antennae) but are smaller.

Adults – Wingless forms are light green to yellow. Winged forms are pale to dark green with a large dusky blotch on the abdomen. The body of the winged form is much slimmer with large oval shaped clear wings. The rear of the green peach aphid has 3 extrusions of the body wall called cornicles.

Biology

GPA has a complicated life cycle. Within a single growing season, GPA populations will have multiple asexual generations. GPA overwinters as an egg on the bark of fruit trees, specifically peach, cherry, apricot, and plum.

Egg hatch occurs on fruit trees about the time of peach bloom. GPA has both a sexual and asexual form. The majority of reproduction occurs asexually by a process called pathogenesis, where live young (females only) are produced by unmated females, called stem mothers.

Development occurs very quickly, growing from neonate to adult in as few as 5 days. At some point during the summer, winged adults develop which disperse to alternate hosts including many vegetable crops. Generations developing on vegetable crops will have both winged and wingless adults and reproduce asexually. In late August winged forms will migrate back to fruit trees.

Near the end of the growing season on fruit trees, sexual forms of the green peach aphid appear for the first time. After mating the female green peach aphid will oviposit eggs on the bark of fruit trees. GPA may have 10+ generations in a growing season.

Monitoring

Beginning at petal fall, inspect the undersides of leaves for new colonies. For faster inspection, shake limbs over a cloth tray (“beating tray”) to observe the dislodged insects.

It is important to identify parasitized aphids, which result in mummies. The presence of mummies (see picture of parasitized GPA) indicates that parasitic wasps are actively attacking aphids.

Economic threshold: Treat peaches when there are two or more colonies per tree before shuck split, or six or more colonies per tree after shuck split. 

Management

Aphid population levels are heavily influenced by temperature, rainfall, numbers of natural enemies present and frequency/type of pesticide application. Aphid outbreaks are most frequent in hot dry weather. Heavy rains will often reduce the aphid population below the economic threshold.

Aphid predators and parasites usually keep populations low. The most common are lady beetles (adults and larvae), syrphid fly larvae, green lacewing larvae, and tiny parasitic wasps that lay their eggs in the aphids. The wasp larvae develop in the aphids eating the inside parts and turning the aphids into empty shells called "mummies". There are many parasitoids attacking the green peach aphid with, perhaps, species of Aphidius and Aphelinus, the most important. 

When pesticides are applied care should be taken to select pesticides that are not damaging to natural enemies of aphids. Because aphids reproductive rate is greater than their natural enemies, incorrect pesticide use may contribute to aphid outbreaks by removing the natural enemies. 

Overview

Both as adults and as grubs (the larval stage), JB is a destructive plant pest. Adults feed on the foliage and fruits of several hundred species of fruit trees, ornamental trees, shrubs, vines, and field and vegetable crops. Adults leave behind skeletonized leaves and large, irregular holes in leaves. The grubs develop in the soil, feeding on the roots of various plants and grasses.

The adult JB is 1/4 to 1/2 inch in length and has a shiny, metallic-green body with bronze-colored outer wings. The beetle has six small tufts of white hair along the sides and back of its body under the edges of its wings. Their eggs are yellowish-white, elliptical or spherical in shape, and are laid about 3 inches into the soil in grassy areas, often in closely cut grass. The grubs can be recognized by the distinctive C-shape they take when curled up. They are white or cream in color, have three pairs of legs, and a hard brown head. The grub stage is about 10 months long. They then go into a brief pupa or resting stage in late spring where they change into a beetle.

Biology

The JB has only one generation per year, but these beetles emerge over a long period from early July through late August and they live for over 30 days. JB overwinters as third-instar larvae in the soil, approximately 12 to 18 inches deep. As soils warm in the spring, larvae migrate to the top 1 to 2 inches and resume feeding on grass rootlets. Larvae begin pupation by mid-June. Warm, sunny days draw beetles out in larger numbers. During the feeding and mating period, females intermittently leave plants, burrow about 3 inches into the ground nearby host plants and lay a few eggs. This cycle is repeated until the female lays 40 to 60 eggs. Larvae migrate downward before the soil freezes to overwinter.

Monitoring

Traps are available for JB but are only effective for monitoring the initial adult emergence. Adults may be monitored by quietly moving into the tree, jarring several branches, and observing how many fly off. Direct fruit counts are the most effective way of assessing the level of damage. Since feeding may be "clumped" or unevenly distributed, care should be taken in looking at a representative sample before making a spray decision. If feeding exceeds 1 percent, then treatment is justified. 

Management

Control of adults can be difficult. Insecticides can reduce damage, but applications may need to be repeated every three to four days since new migrations of beetles can occur daily. Insecticide options include broad-spectrum and reduced-risk. Do not spray when trees are in bloom.

Mass trapping systems have been developed for use against JB under certain situations e.g., organic orchards, in rural areas. Contact Dr. Jaime Piñero at jpinero@umass.edu for more information about mass trapping as an organic management method for Japanese beetles.

Overview.

The adult LPTB is a clear-winged, metallic-blue moth that has two or more yellow bands across the abdomen, giving it a wasp-like appearance. In the Northeast, LPTB causes comparatively less damage than PTB. Peach, nectarine, and cherry are the preferred hosts of LPTB, but all stone fruits may be attacked. Injury by LPTB is almost always associated with previous tree injuries such as incidence of Cytospora canker and, to a lesser extent, pruning wounds, winter injury, and mechanical damage.

Biology.

LPTB overwinters as a larva in various stages of development ranging from young to nearly full-grown. In the spring, larvae resume feeding, complete their development, and pupate. Adult emergence usually takes place around shuck-split or shuck-fall and continues for several weeks. 

LPTB attack higher on the trunk and scaffold branches, especially where there are injuries and callus tissue. The flight period for LPTB is about June 1st through late August, depending on the region. Moths are active during the day, with mating and oviposition occurring soon after emergence. Female moths are attracted to damaged and previously infested trees and deposit eggs in cracks or under bark scales of wounded sites.

Monitoring.

LPTB adults can be monitored using pheromone traps.  Use at least 2 traps per block to determine adult flight.  Install LPTB traps by petal fall. Populations seldom need treatment when trap catches peak at less than 10 moths/trap/week. Use of monitoring traps is recommended in combination with mating disruption.

Inspect wounded areas on the upper trunk, scaffold limbs and branches for larvae and empty pupal cases protruding from the bark. An early sign of LPTB injury is the presence of wood chips, sawdust, and frass
produced by feeding borers in the gum in cankered areas. Control is recommended if 1-2 larvae or empty pupal cases are found per tree.  

Management.

Mating distruption and insecticides are two control options for growers.

For mating disruption, use Isomate PTB-Dual at a rate of 150 pheromone ties per acre.  Dispensers should be deployed at shuck split before LPTB moth flight begins. Use a higher rate (200-250/A) for outside edges of border rows, areas that haven’t been disrupted before and have high populations, and in blocks smaller than 5 acres. Larger blocks are better sites to use this control method compared to small (especially long, narrow) ones. 

When applying insecticides for LPTB, cover the trunk and scaffold limbs using a hand-gun with low pressure and high volume. Ideally, protect the trees for the entire period when the females could be laying eggs. If peachtree borer is also a problem, then the insecticide spray should be made within the first 2 weeks of September. If only LPTB is present, sprays may be applied to late maturing varieties in early August.

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, 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 may have 3-5 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 just before bloom. 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.

Trap threshold: In peaches, if there are >15 moths per trap per week for the first flight, there could be potential fruit infestation problems if control steps are not taken. The suggested trap threshold for OFM in peaches for 2nd - 4th  flight is 10 moths per trap per week. High trap counts do not trigger an immediate insecticide application; there is a lag period for egg hatch after the moths fly.

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 in peaches is recommended at 175 DD (base 45°F) after biofix. However, this 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 depends 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

PTB attacks all stone fruits, particularly peach and nectarine. Female moths are dark blue with a broad orange band around the body and forewings darker than the clear hind wings. The male is smaller and has three to four narrow yellowish bands across the body; both pairs of wings are clear. 

PTB larvae burrow into the bark, usually entering at a crack or wound near the soil surface. Larvae feed on the cambium and tunnel between the inner bark and the sapwood. Larvae normally attack the tree trunk between 7.5 cm (3 in) below ground to 25 cm (10 in) above ground; larger roots are occasionally attacked. Areas attacked often have masses of gum, mixed with frass, exuding from the bark. Young trees may be completely girdled and eventually die; older trees are debilitated and more susceptible to other insects or diseases.

Biology

PTB has a single generation per year. PTB overwinter as partially grown larvae, in a gallery under the bark - usually close to or below ground level. Most larvae complete their development during June and July. Most adults emerge and mate, and females oviposit, during July and August on tree trunks, in cracks or under bark scales, and in soil near the tree trunk.

Monitoring

Pheromone traps can be used to monitor PTB. Captures peaking at less than 10 moths per week generally indicates low pest pressure. Also, inspect the base of the tree for gum containing frass and sawdust. 

Management

Mating disruption. The Isomate PTB Dual mating disruption pheromone dispensers release pheromones for 100 to 120 days and should be placed in the orchard before moth emergence in early June. For effective control of this pest, use at least 200 dispensers per acre, distributed uniformly throughout the entire block. The Isomate PTB Dual dispensers will also control LPTB, but they need to be placed in the orchard earlier in the spring before adult LPTB emergence. 

Insecticides. Recommended treatments include root dips for new plantings and sprays targeting the lower 18 to 24 inches of the trunk. Roots should be dipped in an insecticide solution before planting. Protective trunk sprays with products containing chlorpyrifos should be applied in the summer from the lower scaffold branches to the soil line.

Overview

Biology

• Adult PCs typically overwinter in wooded lots adjacent to peach orchards or around fence rows from where they immigrate into peach orchards in the spring beginning around bloom.

• 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 that allows adult PC to migrate into orchards before and after bloom.

• The female makes a crescent-shaped cut in the skin of the fruit and then lays eggs under the flap of skin. This results in D-shaped scars on the fruit surface. 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.

• Larvae may feed on the fruit for 2–3 weeks before they burrow into the ground to pupate. Adults emerge in mid- to late-summer to cause more feeding damage on mature fruit before they overwinter.

Monitoring

• Fruitlets should be monitored beginning at about 5 mm diameter along orchard borders to determine if new injury is occurring. 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.

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 adults 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. 

Overview

Several species of insects with piercing-sucking mouthparts that feed on peaches early in the growing season can cause a gnarling and distortion of the fruits called catfacing. Fruit is deformed because areas around feeding sites grow more quickly than the damaged parts. Early-season feeding damage from TPB causes raised and sunken corky areas free of fuzz on the surface of the peach fruit. Late-season feeding results in stings with gummy ooze.

TPB is one of several bugs (order Hemiptera) that can produce fruit catfacing. TPB feed on a wide range of crops. TPB is most often a problem in fruit orchards with ground cover comprised of broadleaf weeds, or in orchards near alfalfa fields or other host plants.

TPB adults are about ¼ inch long, oval, and somewhat flattened. Color ranges from green to dark brown, flecked with white, yellow, reddish brown, and black markings. Nymphs (immature stages) are pale yellow to green. Mouthparts are the piercing-sucking type; the beak is three- or four-segmented, arises on the front of the head, and is held below the body, between the legs, when not in use. Nymphs are generally similar to adults but do not have wings.

Biology

TPB overwinter as adults in leaf litter, plant debris, and brush piles, and move to broadleaf weeds, grasses and crops to lay eggs in the spring. TPB adults are strongly attracted to orchards with winter annual weeds in bloom. The nymph is pale yellow or green. It resembles the adult but is smaller and has no wings. It develops through five instars. The third to fifth instars have distinct spots on the thorax and abdomen. The fourth and fifth instars begin to develop brown pigment and larger wings resembling the adult TPB.

Monitoring

White sticky traps are available for monitoring TPB adults. White cards are hung out about two feet from the ground from an outer branch at silver tip and checked preferably twice a week. Traps (one per three to five acres) should be placed at the edge of the block. The economic threshold s 2.4 TPB per trap by tight cluster and 4.1 per trap by late pink. Monitoring in peaches and nectarines is critical at petal fall to shuck fall.

Management

When trees are at the vegetative stage, low densities of TPB can be tolerated. As the trees begin to set buds, chemical controls may be needed. On stone fruits, insecticide applications at petal fall, shuck fall, and 10 days after shuck fall typically provide good control. Applications during pink are often unnecessary because most fruit injured at this time aborts. In comparatively larger blocks, border rows can reduce TPB numbers and level of damage.

Overview

White Prunicola Scale (WPS) is a serious pest of Prunus, especially in temperate areas. In upstate NY orchards, Cornell University researchers  have reported the presence of WPS, which seems to be a closely related species of White Peach Scale (Pseudaulacaspis pentagona) found in the southeastern United States. The WPS is more common in temperate climatic zones.

Infestations are characterized by numerous white scales that cluster on the trunk and scaffolds, giving them a whitewashed appearance. Feeding reduces tree vigor, and foliage of affected trees may become sparse and yellow. Heavy infestations can cause death of twigs, branches and entire trees if left unattended.

Biology

WPS overwinters as an adult female and deposits eggs in the spring. In northern Pennsylvania, the scale is bivoltine (two generations per year).  

Monitoring

Monitor crawler emergence with black electrician's tape wrapped around scale infested branches with the sticky side out. A thin coating of petroleum jelly will enhance and extend the tape's effectiveness in capturing crawlers.

Management

Horticultural oil is recommended as a dormant spray in April, and insecticides can be used against crawlers in mid-June through early July (about 700–1150 DD base 50°F from March 1).

Overview

• Bacterial spot (aka bacterial shot hole, bacterial leaf spot and black spot), Xanthomonas campestris pv pruni favors warm, humid conditions during the growing season and can manifest on leaves, twigs and fruit.
• The bacteria overwinter in twig cankers, and buds, and have been shown to survive epiphytically on twigs and buds. 
• Infections begin around late bloom to petal fall during rain events that cause splash dispersal of the bacteria to susceptible tissue.  Initiated infection lead to reinfection throughout the season when conditions are conducive.
• Symptoms on leaves begin as grayish, water soaked areas on the lower side. Lesions begin as small, dark angular spots, which become necrotic and often these spots will drop our leading to the “shot hole” appearance.  Additionally, early season fruit infections can lead to lesions on the skin.
• Cultural controls are important to reducing over all disease. Some resistant varieties include (but are not limited to): Loring, Redhaven and Madison.  Chemical control begins with a late dormant copper application.  Antibiotic applications begin at petal fall; however, avoidance by way of resistant cultivars is the best line of defense. 

More information

New England Vegetable & Fruit Conference December 2105 presentation by Kari Peter: BACTERIAL DISEASES OF STONE FRUITS: SPOTS AND CANKERS

Overview

• Brown rot is caused by two fungi in the northeast: Monolinia fructicola and M. laxa (causal agent of European brown rot): with M. fructicola being the most common of the two pathogens in New England. 
• The fungus overwinters in mummies and cankers created by the previous season’s infections. 
• Infections are dependent on the presence of inoculum in the orchard, temperature and wetness.  Optimum development temperatures range from 55°F to 70°F (13°C-21°C) with required wetness times decreasing as temperatures increase.  Below 40°F (4°C), infection is delayed, but not necessarily prevented.
• Damage from these pathogens manifests as blossom and shoot blight and fruit rot.  Fruit rots both on the tree and post harvest.  When conditions are right, this can result in significant crop loss
• Cultural management includes removal of mummies and twig cankers during pruning.  Additionally, thinning fruitlets prior to pit hardening (60 days from bloom) can reduce inoculum for later season infection due to rapid decay of infected material.  Chemical control is achieved through targeted fungicidal applications during bloom and fruit ripening.

Overview

Symptoms

Disease cycle

Management

Overview

• caused by fungus Cladosporium carpophilum
• also infects apricot and nectarine
• typically of minor importance in New England
• affects appearance and market value of fruit and can be entry point for brown rot

Symptoms

• olive to black spots velvety spots on fruit, twigs, and leaves
• on fruit has a tendence to be more severe on near stem end
• lesions can combine to form larger areas of disease and can result in fruit cracking
• shoot and twig infections are slightly raised and round to oval, brown in color with purple margins later in the season

Disease cycle

• overwinters in the tree as twig infections
• infection begins at shuck split and peaks in 2 to 6 weeks with high humidity
• fungus is air- and water-borne
• fruit is susceptible to infection from shuck split until harvest

Management

• prune to maintain air movement in canopy
• where a problem, fungicide sprays (Bravo at shuck split, Captan applied thereafter, sulfur) at 10 to 14 day intervals should begin at shuck split and continue until 40 days before harvest

Bacterial Leaf and Fruit Spot

The foliage and fruit of many plum, peach and apricot varieties is susceptible to infection by bacterial leaf spot, Xanthomonas arboricola, that causes small yellow spots and a shot-hole appearance in foliage.  Fruit infection leads to round, sunken spots that detract from the appearance and marketability of fruit.  These symptoms can be confused with spray injury.  Warm weather and moisture favor its spread, as do nearby susceptible peach and apricot trees.  Other names for this disease are bacterial shot-hole and bacteriosis.

Plum and peach varieties vary in susceptibility. Shiro and Early Golden have a high degree of susceptibility. Obilinya and Vanier have some resistance. In general, European plums are more tolerant than Japanese varieties. The most effective management strategy is to plant resistant varieties of plum and peach since chemical sprays are of limited use in preventing this disease.  Removal of branches and limbs with cankers during dormant pruning can reduce disease pressure. 

In early summer, signs of bacterial leaf spot first appear as watersoaked spots on the leaves. The shape of the spots is more angular than round. They eventually turn yellow and fall out which creates the shot-hole appearance. The shot-hole effect is more pronounced on plum than peach, whereas in peach, the lesions turn brown with extended areas of yellowing.  Fruit infections lead to sunken spots that easily crack with fruit expansion.

Copper sprays are more effective for prevention than control, and are of limited use due to phytotoxicity.  Consequently, planting resistant varieties is the most effective management strategy. 

• Black knot infections occur in springtime during the active phase of shoot growth when rainfall favors the spread of this fungus. Wild cherry and plum serve as alternate hosts, spreading the disease to cultivated plums and making chemical control more difficult in susceptible varieties.
• This disease is common in plum orchards. Symptoms appear in new shoots as green swellings of the stem and oddly shaped growths covering the shoot that eventually turn black with warty surface.  In severe cases, the fungus girdles the branch.  Cultivated plums vary in susceptibility with Stanley and Methely being highly susceptible, and Obilinaja fairly resistant.
• The most important period for black knot sprays is from white bud to shuck split.  Infections require rain and are favored by temperatures above 55 F.

Disease Cycle and Management

Black knot is caused by the fungus Dibotyron morbosum, also known as Apiosporina morbosa.  It overwinters on infected trees, and is common on wild cherry and wild plum, as well as, ornamental stone fruit species.  Dispersal occurs from ascospores released during rain beginning soon after budbreak at the green cluster stage and continue throughout shoot elongation which continues into summer, but most occur just before and during petal fall.  Symptoms become visible in fall.  Initially, infections appear as green swellings on new shoots, but they eventually turn black in their second year.  Elongated swellings that can vary in length from 1 to 12 inches. Because of their green color, it is easy to miss infections in their first year.  The knot continues to develop through the second summer with ascospores maturing the second winter after infection. 

Infections will affect the woody part of the tree, so with severe infestation, there is a yield reduction. Once established in an orchard, it is difficult to control solely by chemical means. Well-time fungicide sprays can prevent infection. However, where wild infected hosts are near the orchard, complete control is not possible in susceptible varieties.  In this case, infections should be removed during dormant pruning by cutting back several inches into healthy tissue.

Activity Rating of Fungicides

• Copper (Cuprafix, etc.) - slight
• Captan - good
• Chlorothalanil (Bravo) - excellent
• Sulfur (Microthiol Disperss, etc.) – none (ineffective)
• Thiophanate-methyl (Topsin M) - fair

Nonchemical control is primarily by removing wild plum and cherry, and by removing infections during pruning.  Where this is not possible, select varieties with partial to complete resistance:

Spring Satin plumcot, Obilinaja, Early Italian, Green Gage, Fellenberg, and President.

• 
  Strong resistance to brown rot does not exist in commonly grown varieties, but plums are generally not as susceptible as peaches.  However, European plums are more susceptible than Japanese plums. 
• The brown rot fungus infects flowers when wet weather occurs during bloom and infects fruit when warm, wet weather occurs during the ripening stage. Infected fruit that is not harvested will dry and persist into the next season to continue the spread of infections, and should therefore be removed during dormant pruning.  
• Fungicides applied to protect blossoms and ripening fruit should be timed according to susceptibility and weather that favors disease.

Disease Cycle and Management

Brown rot, a fungal disease caused by Monilia fruiticola, infects blossoms, shoots and fruit, and causes significant losses for growers when not controlled.  Plums are less susceptible to brown rot than peaches and cherries, but can be severely infected when conditions are ideal for the fungus.  The brown rot fungus overwinters on mummified fruit that remain attached to twigs, infected blossoms that cling to twigs and on infected shoots.  Fungal conidia are dispersed by wind and rain.  The disease is more severe with wet weather. 

Conidia produced on infected blossoms and shoots spread to fruit.  Infected blossoms wilt, turn brown and cling to the shoot.  The infection can move into the twig and cause a canker.  Blossom infections are not common on plum.

Fruit are susceptible to infection.  Immature fruit can be infected when insect control is poor.  Thinned fruit can serve as a source of innoculum, but thinning fruit so that they do not contact each other will reduce disease at harvest.  Signs of infection begin as small, tan colored circular lesions on the fruit surface.  In warm, humid weather, lesions develop conidia, a mass of grayish brown spores over the fruit surface.  During warm, humid conditions, grayish brown spores are produced which can be diagnostic of brown rot.  Infected fruit that remain in the orchard will shriven and cling to the branch, and serve as a source of disease the following spring.  These shriveled “mummies” should be removed during pruning.

The brown rot fungus can be spread by insects and can also spread from alternate hosts such as wild plum and cherry. Improve air circulation with annual pruning and sucker removal.  Thin fruit so that they are not in contact with other fruit.  Harvest fruit before they become over ripe.

Fungicide resistance has occurred.

Activity Rating of Fungicides

• Copper – not applicable
• Captan - good, but phytotoxic to some varieties
• Chlorothalanil (Bravo, Echo) – excellent for blossom blight, not labeled for fruit rot
• DMI (Indar, Tebuzol, etc.) – excellent, except for Rally
• Strobilurin (Pristine) - excellent
• Strobilurin (Flint, Gem) - suppression
• Sulfur (Microthiol Disperss, etc.)– fair for blossom blight, slight for fruit rot
• Biofungicides (Double Nickel, Serifel) - suppression
• Thiophanate-methyl (Topsin M) – not recommended because of resistance

Possible causes are phytoxic fungicides, particularly Captan.  Russetted spots appear in early summer and can be more prevalent on the sun-exposed side of the fruit.  Captan should not be applied from shuck split through early July, and chlorothalonil from shuck split through harvest.