Extended wetting events this week

It has been a wet week at our AREC this past week, with significant infection events five consecutive days, including the one noted in the previous post for June 8-9. These were as follows: June 9-10 (8 hr, mean 70° with 0.02 in. rain); June 10-11 (16 hr, mean 76°, with 0.19 in. rain); June 11-12 (14 hr, mean 70° with 0.11 in. rain); June 12-13 (16 hr, mean 70° with 0.44 in rain). Total rainfall for June 9-13 at our AREC was 1.36 inches but volumes with the several storms varied widely throughout the local area and there was also scattered hail in some locations.

Temperatures and length of wetting during these events favored secondary apple scab and early summer disease development. Cedar rust galls were producing spores through all of these events, but are nearly depleted now. Secondary spread of fire blight was possible where growing shoot tips are still susceptible.

In addition to developing activity by the usual summer diseases, with these recent warmer wetting periods, be alert for possible early indications of Alternaria leaf blotch on Red Delicious and Glomerella leaf spot on Gala, Golden Delicious and Cripps Pink (Pink Lady) apples. This is also a critical time for protection against Brooks fruit spot.

For purposes of predicting development of the sooty blotch and flyspeck (SBFS) fungal complex, we record accumulated wetting hours (CWH) from rainfall or dew, starting 10 days after petal fall. As of Friday afternoon, June 13, we had accumulated 136 wetting hours toward the 250-hour threshold for specific treatment against the SBFS fungal complex. 

Infection conditions for June 9-13 were similar at Tyro, VA. As of June 12, a sensor placed in an apple tree at 1165 ft. elevation had accumulated 90 wetting hours from May 11, while one placed at 941 ft elevation had accumulated 172 hr. The station at the highest elevation (1465 ft) apparently spent some time in the clouds this week and continues to register more wetting hours than the intermediate one, 125 CWH.