Disease conditions May 8-12

Wet weather disease conditions persisted this week with infection periods each day May 8-12: May 8: 8 hours wet at 52-56° with 0.1 in. of rain; May 9: 15 hr wet with 0.1 in. of rain; May 10: 8 hr at 53° with 0.03 in. of rain; May 10-11: 19 hr at 55° with 0.25 in. of rain; May 11-12: 16 hr at 55° with 0.16 in. of rain. This now totals 13 infection periods in 15 days! Several of these infection periods again involved both scab and rusts.

Hopefully, the fruits of most varieties are now big enough that they have become resistant to quince rust . However, Romes and some other varieties with late bloom where there was frost damage might be the exception. There still is some cedar-apple rust inoculum left that could infect the youngest leaves, but the long wetting periods are now depleting much of the rust inoculum. This week we saw cedar-apple rust lesions developing from infection that occurred Apr 22-23. (Photo by Allen Cochran II below).

Early cedar-apple rust symptoms on York apple leaf. May 10, 2016. 

With this amount of wetting during the bloom and immediate post-bloom growth stages, moldy core becomes an unusual concern on varieties such as Red Delicious, Fuji, and Cameo. Moldy core is caused by as many as 14 different fungi that invade during the six-week period that the calyx tube stays open, so broad-spectrum residual fungicide protection is the most effective approach to avoiding this problem. Although the recent volume of rain has not been extreme given the number of wetting periods and hours of wetting that we’ve had, but the conditions have made it difficult to maintain adequate protection the past two weeks.

Fire blight: This week we saw fire blight blossom infection symptoms (shown below) on unprotected York apple trees, resulting from infection that occurred about Apr 20-21. Continue to protect prolonged late bloom as needed. 

Advanced blossom blight symptoms May 10, 2016