Recent scab and rust infection periods and fire blight outlook, May 2, 2016

At our AREC in Winchester, we have had four scab or rust infection periods within the past four days. April 28-29: a heavy apple scab and rust infection period: 31 hours at 53-46° with 0.67 in. of rain; Apr 30: 10 hours at 51° with 0.01 in. of rain; Apr 30-May 1: 18 hours at 53° with 0.53 in. of rain; May 1-2: 12 hours at 59° with 0.16 in. of rain. Locally, some of these wetting periods may have been extended by showers or foggy conditions. Apple blossoms and small fruit are still very susceptible to quince rust so it would be prudent to include a sterol-inhibiting fungicide for after-infection rust control in the next fungicide application.

FIRE BLIGHT: Below is a cropped graphic from the Maryblyt 7 program. Susceptible blossoms are still present on some cultivars. The temperature and rainfall data are current through Monday morning, May 2. Predicted weather conditions are shown for May 2-7. 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. The fire blight risk remains high for May 2-4, and slightly warmer temperatures with wetting could result in infection. For optimum control, a protective streptomycin application is recommended ahead of predicted infection, but it can also provide about one day after infection suppression.

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 risks on late bloom can change quickly with unpredicted warmer temperatures and wetting.