Summer disease update- bitter rot pressures continue

Bitter rot continues to be the summer disease causing the greatest concern. We are now seeing an unusual amount of fruit drop due to bitter rot in unprotected fruit in our research plots. 

Fruit drop from bitter rot in unprotected Idared fruit

Rainfall over the region has been variable the past month. At our AREC we have not had any single rain events totaling as much as an inch (0.73 inch on Aug 3), but we have recorded rain 15 days with a total of 2.35 inches in August. Two of these rains resulted in extended wetting events at our AREC in Winchester: Aug 7, wet 14 hr at 65° with 0.43 in. of rain and Aug 12, wet 18 hr at 76-66° with 0.23 in. of rain. While the volume of rainfall in individual events has not been excessive, their frequency and brief intensity requires continued regular fungicide coverage to replenish depleted residues as we approach harvest. Our research plots show good bitter rot and general summer disease control where we have maintained good coverage with various fungicide programs. 

For the record, as an indicator of the development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours from rainfall or dew. As of Aug 25, accumulated wetting hours (ACW) since May 4 are now: at 909 ft elevation, 715 hr (with the 250-hr threshold reached Jun 7; sooty blotch first observed Jul 7); at 932 ft (the AREC NEWA station), 486 hr, threshold reached Jul 5; and at the 983 ft elevation, 410 hr ACW, threshold reached Jul 21. These totals are 90 ACW less than last year at the highest elevation and 141 ACW less than last year at the lowest elevation.

As we approach harvest, fruit maturity of earlier varieties such as Ginger Gold and Gala seems to be running about a week early. We are seeing good fruit size, and we are optimistic about good fruit coloring weather, with the 2-week forecast showing most night temperatures with lows in the 50s.