Bitter rot observed at Winchester; Sooty blotch and flyspeck thresholds reached at Winchester and Tyro, VA.

For predicting the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew, starting 10 days after petal fall. This year we began wetting hour accumulation at Winchester from May 14. As of Monday, July 4, the 250-hr accumulated wetting hour threshold (ACW) has been surpassed at all of the wetness sensors at our AREC and at Tyro, VA.

At Winchester ACW: at 909 ft elevation, 442 hr (with the 250-hr threshold reached June 5); at 952 ft elevation, 341 hr (near the threshold); and at the 983 ft elevation, 280 hr ACW. At Tyro, VA we started wetting hour accumulation May 4, and as of July 4, a sensor placed at the 941 ft elevation had accumulated 426 hr (with the 250-hr threshold reached June 6); the one at 1165 ft. elevation had accumulated 264 wetting hours, and the one 1465 ft. elevation had accumulated 280 wetting hours. 

At Winchester in the past two weeks we had three significant extended wetting events favorable for SBFS and fruit rot development: June 23: 9 hr at 66°, with 0.55 in. rain, and June 27-28: 14 hr at 80-72° with 0.08 in. rain, and July 3-4: 17 hr at 68° with 0.02 in. rain. Bitter rot was observed in Honeycrisp apples at Winchester as early as June 22. Specific treatment against the SBFS fungal complex and rot diseases is advised.

Summer disease management should be directed toward the array of potential problems in specific orchard blocks, utilizing protective fungicides for general purposes, but supplementing them with more specifically active fungicides directed at higher disease pressures and special control problems. Expect higher fruit rot pressures where fire blight killed shoots and fruit mummies are present in the trees. For more information on the effectiveness of apple fungicides for management of sooty blotch/flyspeck, Brooks fruit spot, black rot, white rot and bitter rot consult Table 6 (pp. 53-54) in the 2016 Spray Bulletin for Commercial Tree Fruit Growers.