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Bacterial spot

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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