Friday, July 21, 2017

Summer disease update, July 21.

Overall, conditions remain generally dry, and some good soaking rains would be welcomed for fruit and other crops in the Winchester area. This week we had one extended wetting event at our AREC in Winchester: Jul 17-18, wet 11 hr at 71°  but with only 0.1 in. of rain. As an indicator of earlier wetting conditions, we are now seeing sooty blotch, Brooks fruit spot, and bitter rot on unprotected apple fruits at our AREC . A bright spot in the situation is for ripening peaches, where reduced volume of rainfall should increase sweetness and, hopefully, reduce brown rot pressure.

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 from May 4, 10 days after petal fall. While we have been lacking volume of rainfall, we continue to accumulate wetting hours at lower elevations in the orchard. As of Friday morning July 21, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 439 hr (with the 250-hr threshold reached Jun 7; sooty blotch first observed Jul 7); at 932 ft (the AREC NEWA station), 309 hr, threshold reached Jul 5; and at the 983 ft elevation, 250 hr ACW.  The significance of the 250-hr threshold is that it predicts that the fungi causing SBFS symptoms are now present on unprotected fruit, and that is confirmed by symptoms at our AREC.

For Nelson County in central Virginia, the petal fall date was Apr 20, and accumulation of wetting hours from Apr 30 is recorded by weather stations at different elevations at Tyro. As of July 7, a sensor placed at 1465 ft. elevation had accumulated only 98 wetting hours from Apr 30, while the one placed at 941 ft elevation had accumulated 448 hr, with the 250-hr threshold reached on June 12).

The NEWA station at Gadino Cellars (elev. 665 ft, in Washington, VA) passed the threshold of 250 ACW June 16, and has now recorded 360 wetting hours since May 1. A NEWA station at Fishersville also passed the 250-hr threshold June 16 and now has 334 ACW. Three Albemarle County NEWA stations have also passed the 250-hr threshold, listed with ACW as of July 21 and date the was threshold reached Batesville (313 ACW, July 2); Crozet (277 ACW, July 5); Carter Mt. (259 ACW, July 6).