Preliminary studies for controlling bacterial spot in low-chill peaches

Florida's subtropical climate allows peach trees to retain their leaves for most of the year. Vegetative growth begins in late January or early February and trees can retain their leaves until December. Symptoms of bacterial spot (Xanthomonas arboricola pv. pruni (= X. campestris pv. pruni)) often occur on foliage and fruit in May. The disease persists and develops rapidly under warm weather, and complete defoliation can occur by October on susceptible cultivars. Copper-based bactericides can be used during dormancy and early in the growing season. However, the risk of phytotoxcity from copper sprays increases as the season progresses. A spray program was developed during the summer of 2004 and repeated in the summer of 2005 in an attempt to control bacterial spot. Basic copper sulfate (Cuprofix Disperss((R))) at a rate of 0.08 oz (23 g) /200gal H2O applied at 400 gpa, was used in the experiment along with a soy-based non-ionic surfactant and a pH reducing agent. The spray program began in early June just prior to summer pruning and just after final fruit harvest had been completed. Trees were sprayed on a three week schedule until early October. Preliminary observations indicate the copper sprays delayed and significantly reduced defoliation. This spray program may help alleviate the condition of "fall bloom" which can occur in some trees when they defoliate too early. Overall health and tree vigor may also be increased from a longer photosynthetic period.