Xanthomonas campestris

Written by: 

Elizabeth Garofalo

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

Monilinia fructicola

Written by: 

Elizabeth Garofalo

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.

Peach, nectarine

Written by:

Dr. Renae Moran

This disease, caused by a fungus, infects leaf buds in spring at bud break.  Foliage shows signs of infection later during rapid shoot growth.  It is not much of a problem in managed orchards unless fungicide applications are skipped in years with no crop. Fruit infections are uncommon. 

Symptoms

Leaf puckering, yellowing and orange discoloration in severe cases are indicative of leaf curl infection. Shoots outgrowth the infection in mild cases, but severely infected shoots might not survive winter.  Infected foliage drops in summer. 

Disease cycle

Spore dispersal my splashing rain and wind.  Spores overwinter on the tree in the cracks and crevices.  Spore germination in spring coincides with bud swell through bud opening. Wet weather at this time leads to leaf tissue infection.   Leaves that unfold outside the bud are not susceptible to infection, so later in spring and through summer, infections will not occur.

Management

Resistant varieties are an option and should be a consideration for organic or low-spray orchards. Severe infections can weaken trees.  Elberta, Harken and Redhaven have partial resistance. 

A fungicide application in fall just prior to leaf drop or in spring just prior to bud break. Regular fungicides for other problems will substantially reduce the prevalence of this disease.  Fixed coppers, lime sulfur, chlorothalonil and Bordeaux mix are effective fungicides.  Once infected, fungicides are not effective at managing this disease. Chlorothalanil is not labeled for use on apple.  Copper compounds will also suppress bacterial spot.

Peach leaf curl - Taphrina deformans

Cladosporium carpophilum

Written by: 

Elizabeth Garofalo

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