Heavy scab and possible rust infection period; fire blight outlook

As of 8 AM April 29 we had recorded a heavy apple scab and possible rust infection period: 30 hours at 53-46° with 0.44 in. of rain. The cedar galls and quince rust cankers are now in "full bloom", producing basidiospore inoculum, and the apple blossoms and small fruit are very susceptible to quince rust. The first 12 hours of wetting at 53° would have have been more favorable for infection by the rusts than the later 18 hours with temperatures down to 46°. With continued sporadic wetting in the 50s likely, it would be prudent to include a sterol-inhibiting fungicide for after-infection rust control in the next fungicide application.

Maryblyt outlook for Winchester, VA, April 29.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Susceptible flowers are still open on many cultivars. The temperature and rainfall data are current through Friday morning, April 29. Predicted weather conditions are shown for April 29-May 2. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial populations), W (wetting by rain or dew), and T (average daily temperature 60 F or above). Based on predicted temperatures, the risk column shows infection conditions for Apr 21, 22 and 24-26.

 Cooler temperatures Apr 29-30 should reduce risks through Apr 30, but predicted warmer temperatures Sunday, May 1 will again increase the risk going into next week. For optimum control, a protective streptomycin application is recommended ahead of predicted infection, but it can also provide about one day after infection suppression. Risk can change quickly with unpredicted warmer temperatures and wetting.

The weather conditions used in the predictive part of this graphic come from the Weather Channel for Winchester, supplemented by site-specific data from SkyBit Inc. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. The fire blight outlook will be updated Monday, May 2.