Saturday, July 6, 2019

Variable summer disease pressures

Summer disease pressures the past month have been generally lighter at Winchester than in other parts of Virginia. 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 chose May 2 as the petal fall date for Winchester, so the start of wetting hour accumulation (ACW) was from May 12. Wetting hours accumulated quite rapidly in May, but more slowly in late June and early July; however, rains the past two days have brought the total ACW (234 hrs) approaching the 250 hr threshold with more rain expected through the weekend. ACW is similar to Winchester at Roanoke (239 hr).

Other areas of Virginia generally had more rainfall than Winchester and more wetting hours in June. Examples, with ACW totals, are: Staunton (377 hr); Rappahannock County (Gadino Cellars) 319; Red Hill (733 hr); Lynchburg (480 hr); Floyd (331 hr); Danville (548 hr). 

At our AREC in Winchester we recorded only three extended wetting events since the posts early last month: Jun 13 (10 hr wet at 59° with 0.19 in. rain; Jun 24 (9 hr wet at 74° with 0.54 in. rain); and Jul 4-5 (16 hr wet at 70° with 0.74 in. rain). Other local areas experienced thunderstorms which resulted in more total rainfall and, especially where those occurred in the evening, more ACW.