Scab and rust infection period; fire blight; tracking sooty blotch and flyspeck development

We recorded another apple scab and cedar-apple rust infection period at our AREC May 29-30: 22 hours wetting with 0.6 inches of rain at 55-58°.

Last week we had several reports and observations of fire blight outbreaks. The onset of symptoms and local temperature history over the past several weeks indicate that these probably dated back to secondary infection that occurred about May 13, when there were some strong storms in the area.

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 8 as our petal fall start date for Winchester, so the start of wetting hour accumulation is from May 18. This is 5 days later than 2013 and 30 days later than 2012. By the end of the wetting period Friday, May 30, we had accumulated 33 wetting hours toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex. 

A caution to those further south and east of the Blue Ridge: Your petal fall date may have been a week or more ahead of ours and we have arbitrarily selected May 11 as the start date for accumulation of wetting hours by weather stations at Tyro, VA. One of the purposes of having three weather stations at this location was to compare wetting hour accumulation at different elevations. As of May 30, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 50 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 109 hr!