Continued summer disease pressure

Summer disease pressure continued this past week with a pattern of afternoon or evening showers followed by wetting through the night, all at relatively warm temperatures.

At our AREC we recorded five such extended wetting periods with rainfall: July 2, 10 hr wet at 64-73° with 0.16 in. of rain; July 3-4, 15 hr wet at 72-65° with 0.01 in. of rain; July 6, 9 hr wet at 70° with 0.14 in. of rain; July 6-7, 15 hr wet at 68° with 0.04 in. of rain; July 8-9, 15 hr wet at 68° with 0.05 in. of rain (but more than 1 inch in some local areas). These frequent infection periods all favored bitter rot and Glomerella leaf spot development, as well as other rots, and depleted much fungicide residue for sooty blotch and flyspeck control.

Accumulated wetting hours (ACW) at the AREC are related to elevation: at 909 ft elevation, 497 hr; at 952 ft elevation, 390 hr; and at the 983 ft elevation 347 hr ACW. 

At Tyro, in Nelson County, total ACW as of Monday, July 6 were: at 941 ft elevation, 449 ACW; at 1165 ft, 250 ACW; and at 1465 ft, 264 (with the 250-hr threshold reached July 5). Note that the threshold has now been reached at all sensor elevations at Tyro.

The recent frequent wetting periods also favor development of brown rot on ripening peaches.