Answer: The bacterium Xanthomonas pruni overwinters in twigs that are infected late in the season about the time leaves are shed. The following spring, when environmental conditions are favorable, bacteria ooze out onto the surface of these twigs. The bacteria are then spread by windblown or splashing rain and can result in new infections throughout the growing season. The bacteria come in contact with healthy leaves, fruit and current-year twigs and enter the tissues through stomata or lenticels when surface moisture is present. Once inside healthy tissues, the bacteria multiply and disease develops.
Warm temperatures (70-85 degrees F, 2l-29 degrees C) with light rains, heavy dews or fogs and windy weather are most conducive for disease development and spread. The disease makes little progress when weather is hot and dry.
1. When planning an orchard, avoid low-lying or shaded sites with poor air circulation and soil drainage. Any practice that promotes faster drying of fruit and foliage will help reduce the risk of infection. Destroy nearby wild or neglected stone fruits (Prunus spp.). Buy and plant only vigorous, disease-free fruit trees from a reputable nursery.
2. Prune trees annually to allow for better air circulation and to maintain tree vigor. If possible, prune during dry weather in the latter half of the dormant season.
3. Select peach varieties with resistance to bacteria spot. The following varieties are somewhat resistant: Belle of Georgia, Biscoe, Candor, Comanche, Garnet Beauty, Harbrite, Harken, Late Sunhaven, Loring, Madison, Norman, Pekin, Raritan Rose, Redhaven, Redskin and Sunhaven. These varieties are very susceptible: Babygold S, Blake, Elberta, Halehaven, Jersey Queen, Jerseyland, July Elberta, J.H. Hale, Kalhaven, Rio-Oso-Gem, Suncling, Suncrest and Sunhigh.
4.Fertilize where needed to maintain vigorous but not excessive shoot growth.
5.Spray applications. At present, no spray program is completely effective for controlling bacterial spot. In the home orchard, spraying for bacterial spot is not considered practical.
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