Bacterial spot of peach as influenced by water congestion, leaf wetness duration, and temperature

Development of bacterial spot on Suwanee peach leaves after inoculation with Xanthomonas campestris pv. pruni was studied at 24 and 30 degrees C and after-inoculation wetness periods of 0, 6, 18, 24, and 48 h. Water congestion following leaf wetness resulting from exposure to 100% relative humidity for at least 36 h and growing plants in sandy soil were necessary for symptom development. Symptom development was slower at 24 than at 30 degrees C. Postinoculation wetness periods greater than 18 h were necessary for extensive symptom development at 24 but not at 30 degrees C. However, some symptom development was evident at either temperature with no leaf wetness after inoculation if leaves were water-congested. Symptoms did not develop when trees were grown in a sandy loam-vermiculite soil mixture.