Monday, June 20, 2016

Increasing summer disease pressures

At Winchester last week we had two significant extended wetting events favorable for SBFS and fruit rot development: June 15-16: 11 hr at 76-72°, with 0.46 in. rain, and June 16-17: 15 hr at 69-63° with 1.95 in. rain. Much of this rain came at the beginning of the event, and this volume of rainfall would have depleted much of the protective fungicide residue, leaving the fruit exposed to potential rot infection.

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 began wetting hour accumulation at Winchester from May 14. As of Monday, June 20, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 257 hr (with the 250-hr threshold reached June 5); at 952 ft elevation, 248 hr (near the threshold); and at the 983 ft elevation, 218 hr ACW.

At Tyro, VA we started wetting hour accumulation May 4, and as of June 20, a sensor placed at the 941 ft elevation had accumulated 315 hr (with the 250-hr threshold reached June 6); the one at 1165 ft. elevation had accumulated 188 wetting hours, and the one 1465 ft. elevation had accumulated 213 wetting hours. 

At both Winchester and Tyro, most of the wetting hour accumulation at the higher elevations has been only with rain events, while accumulation at the lowest elevation has been with dew as well as rain events.

Summer disease management should be directed toward the array of potential problems in specific orchard blocks, utilizing protective fungicides for general purposes, but supplementing them with more specifically active fungicides directed at higher disease pressures and special control problems. Expect higher fruit rot pressures where fire blight killed shoots and fruit mummies are present in the trees. For more information on the effectiveness of apple fungicides for management of sooty blotch/flyspeck, Brooks fruit spot, black rot, white rot and bitter rot consult Table 6 (pp. 53-54) in the 2016 Spray Bulletin for Commercial Tree Fruit Growers.

Tuesday, June 7, 2016

Sooty blotch/flyspeck thresholds reached at Winchester and Tyro; extended wetting events


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 began wetting hour accumulation at Winchester from May 14. As of Monday, June 6, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 257 hr (with the 250-hr threshold reached June 5); at 952 ft elevation, 194 hr; and at the 983 ft elevation, 185 hr ACW.

At Tyro, VA we started wetting hour accumulation May 4, and as of June 6, a sensor placed at the 941 ft elevation had accumulated 245 hr (with the 250-hr threshold reached June 6); the one at 1165 ft. elevation had accumulated 173 wetting hours, and the one 1465 ft. elevation had accumulated 200 wetting hours.

The sensors at the higher elevations at both Winchester and Tyro could reach the threshold ACW within the next week or two, and similar accumulations should be expected for the Carroll-Patrick, Roanoke-Botetourt and Rappahannock-Madison fruit production areas.

At Winchester we had two more extended wetting events at relatively warm temperatures favorable for SBFS and fruit rot development and secondary scab infection last week: June 2-3: 19 hr at 75-64°, with 0.3 in. rain,  and June 4-5: 16 hr at 75-67°.

Wednesday, June 1, 2016

Extended wetting events May 24-31 and accumulated wetting hours

We had five extended wetting events the last week of May, and temperatures of several of these ranged into the high 60s and 70s, favorable for summer diseases as well as secondary scab infection: May 24, 9 hr wet at 57-50° with 0.04 in. of rain, May 26-27, 12 hr wet at 70-64° with 0.08 in. of rain, May 27-28, 15 hr wet at 73-63° with 0.2 in. of rain,  May 29-30, 15 hr wet at 73-61° with 0.04 in. of rain and May 30-31, 12 hr wet at 72-60° with 0.04 in. of rain.

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 again chosen May 4 as our petal fall date for Winchester, and the start of wetting hour accumulation is from May 14. As of Monday, May 30, accumulated wetting hours (ACW) toward the 250 wetting hour threshold for specific treatment against the SBFS fungal complex were: at 909 ft elevation, 172 hr; at 952 ft elevation, 128 hr; and at the 983 ft elevation, 116 hr ACW.

At Tyro, VA we started wetting hour accumulation May 4, and as of May 30, a sensor placed at 1465 ft. elevation had accumulated 153 wetting hours, the one at 1165 ft. elevation had accumulated 124 wetting hours, and the one placed at 941 ft elevation had accumulated 175 hr.

Mildew-susceptible cultivars are showing considerable secondary infection, a result of the earlier 28 dry weather mildew infection days through May.