Wednesday, June 13, 2018

Extended wetting events; sooty blotch/flyspeck threshold reached, early bitter rot activity

In the past week at  our AREC in Winchester we recorded two extended wetting events: June 10-11, with 15 hr of wetting at 59° with 0.51 in. rain; June 11-12, with 15 hr of wetting at 59° with 0.01 in. rain. These wetting events favored early summer disease activity on apples, peach scab, cherry leaf spot and brown rot on ripening cherries. 

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 June 13, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 276 hr; at 932 ft (the AREC NEWA station), 252 hr; and at the 983 ft elevation, 263 hr ACW. This year the wetting hours have been more a result of rainfall rather than wetting from dew, so wetting hour accumulation at different elevations is quite similar, and all have reached the 250-hr threshold. 

For central Virginia, we selected Apr 24 as the petal fall date for accumulation of wetting hours by weather stations at Tyro. As of June 13, a sensor placed at 1465 ft. elevation had accumulated only 172 wetting hours from May 4, while the one at 1165 ft. had accumulated 228 wetting hours, and the one placed at 941 ft elevation had accumulated 390 hr, and passed the 250-hr threshold for specific treatment for sooty blotch and flyspeck on May 29. Also east of the Blue Ridge, the NEWA station at Batesville has passed the 250-hr threshold with 328 ACW while the NEWA station at Gadino Cellars near Washington, VA has recorded 261 ACW using May 1 as the petal fall date. 

Two weeks ago various "rot spots" were reported on several apple varieties from central Virginia. Those have now been confirmed as incubating into bitter rot