Monday, June 25, 2018

Early summer disease pressure and continued wet weather

In the past two weeks at  our AREC in Winchester we recorded three more extended wetting events: June 19-20, with 17 hr of wetting at 73° with 0.1 in. rain; June 20-21, with 17 hr of wetting at 71° with 1.44 in. rain; June 21-23, with 35 hr of wetting at 64° with 3.05 in. rain. These wetting events favored early summer disease and rot activity on apples, peach scab, and cherry leaf spot and brown rot on ripening cherries and other stone fruits. 

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 (from May 17 at Winchester). As of 6 AM June 25, all three of our AREC weather stations accumulated more than the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. These totals were: at 909 ft elevation, 391 hr; at 932 ft (the AREC NEWA station), 333 hr; and at the 983 ft elevation, 343 hr accumulated wetting hours (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 25, a sensor placed at 1465 ft. elevation has now reached the 250-hr threshold with 252 wetting hours, while the one at 1165 ft. had accumulated 259 wetting hours, and the one placed at 941 ft elevation has accumulated 466 hr. Also east of the Blue Ridge, the NEWA station at Batesville has passed the 250-hr threshold with 395 ACW while the NEWA station at Gadino Cellars near Washington, VA has recorded 334 ACW using May 1 as the petal fall date. 

We have now confirmed active bitter rot at our AREC (pictured below), and there have been several reports of bitter rot from central Virginia. 
Bitter rot on Honeycrisp apple (Photo by D. Melby)