Summer disease update

Summer disease pressure continued this past week with several extended wetting events at relatively warm temperatures and some locally heavy rainfall.

At our AREC we recorded three such extended wetting periods with rainfall: July 11, 9 hr wet at 71-66° with 0.28 in. of rain; July 13, 9 hr wet at 70° with 0.13 in. of rain (but as much as 4 inches with flooding locally in the Woodstock area of Shenandoah County); July 14, 11 hr wet at 70° with 0.34 in. of rain; . These frequent infection periods with rain deplete fungicide residue and continue to favor development of rots such bitter rot and white rot, as well as Alternaria and Glomerella leaf spots.

As of the Thursday morning, July 15, accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 588 hr; at 952 ft elevation, 467 hr; and at the 983 ft elevation 423 hr ACW. Since accumulation of wetting hours began May 14, this represents an increase of 2.2 wetting hours per foot of elevation drop from 983 to 909 ft!

At Tyro, in Nelson County, total ACW as of Thursday morning, July 15, were: at 941 ft elevation, 531 ACW; at 1165 ft, 299 ACW; and at 1465 ft, 345 (with the 250-hr threshold reached July 5). The 250-hr ACW threshold reached at all sensor elevations at Tyro early last week, and this probably true for all orchards in the central Virginia region.

The recent frequent wetting periods also favor development of brown rot on ripening peaches and other stone fruits.