Extended wetting for scab and summer diseases

An extended wetting period last week, still in progress at the time of the last post June 5, ended at 14 hr wetting at 60°with 0.04 in. of rain. 

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 4 as our petal fall start date for Winchester, and the start of wetting hour accumulation is from May 14. Last week we also had two nights with wetting from dew, totaling 18 hr. With a total of 96 wetting hours last week, our total accumulated wetting hours (ACW) came to 195 hours as of Monday, June 8. The threshold for specific treatment against the SBFS fungal complex is 250 wetting hours. 

A note to those farther south and east of the Blue Ridge: Your petal fall date may have been a week or more ahead of ours and I have updated the start date for accumulation of wetting hours by weather stations at Tyro, VA to May 3. One of the purposes of having three weather stations at this location is to compare wetting hour accumulation at different elevations. As of June 8, a sensor placed at at 941 ft elevation had already greatly passed the 250-hr ACW threshold for a total of 315 hr while the ones at higher elevations, 1465 ft and 1165 ft, had nearly identical ACW of 144 and 140 wetting hours, respectively. 

Alternaria leaf blotch, confirmed on Red Delicious leaves from Rockingham County May 21, continued to advance, as expected, with the extended wetting last week.