Early summer disease activity

For purposes of 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 our petal fall date at Winchester was Apr 24, so the start of wetting hour accumulation was from May 4. As of Monday morning June 5, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 241 hr; at 932 ft (the AREC NEWA station), 180 hr; and at the 983 ft elevation, 143 hr ACW. In the past week most of the wetting hour accumulation was from dew and occurred more at lower elevations in the orchard. Note that at the lowest elevation, the ACW of 241 hr will probably reach the threshold level of 250 ACW this week.

For Nelson County in central Virginia the petal fall date was Apr 20, and accumulation of wetting hours from Apr 30 is recorded by three weather stations at different elevations at Tyro. Wetting hour accumulation in central Virginia was slow last week. As of June 5, a sensor placed at 1465 ft. elevation had accumulated only 76 wetting hours from Apr 30, while the one at 1165 ft. had accumulated 151 wetting hours, and the one placed at 941 ft elevation had accumulated 199 hr.

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) will probably also reach the threshold level of 250 ACW this week, having recorded 238 wetting hours since May 1.

We have had several reports of other early summer disease activity: bitter rot mummies forming on fire-blighted shoots and early Glomerella leaf spot symptoms in central Virginia and Alternaria leaf blotch on Red Delicious in Rockingham County.