Early accumulation of wetting hours approaching the sooty blotch/flyspeck threshold

At our AREC in Winchester we recorded three recent secondary apple scab infection periods:  May 22, with 11 hr of wetting at an average of 67° with 0.24 in. rain; May 22-23, with 7 hr of wetting at an average of 71° with 0.02 in. rain; May 27-28, with 16 hr of wetting at an average of 69° with 0.14 in. rain. Some of the wetting occurred at temperatures near 70° and was favorable for moldy core infection and the start of 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 we have chosen May 7 as our petal fall date for Winchester, so the start of wetting hour accumulation is from May 17. As of 6 PM May 28, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 130 hr; at 932 ft (the AREC NEWA station), 118 hr; and at the 983 ft elevation, 126 hr ACW. One of the purposes of following three weather stations is to compare wetting hour accumulation at different elevations. Typically there is a greater difference between these three locations, but this year many of the early wetting hours this year were a result of rainfall rather than dew, so wetting hour accumulation at different locations is more similar than in some previous years. 

For central Virginia, we have selected Apr 24 as the petal fall date for accumulation of wetting hours by weather stations at Tyro. As of May 28, a sensor placed at 1465 ft. elevation had accumulated only 63 wetting hours from May 4, while the one at 1165 ft. had accumulated 129 wetting hours, and the one placed at 941 ft elevation had accumulated 239 hr, approaching the 250-hr threshold for specific treatment for sooty blotch and flyspeck. Also east of the Blue Ridge, the NEWA station at Red Hill has already passed the 250-hr threshold with 307 ACW. The NEWA station at Gadino Cellars near Washington, VA has recorded 153 ACW since May 10.