FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Some apple cultivars have reached petal fall but others still have scattered bloom, and others, such as Yorks and Romes, are still very susceptible. (The Yorks hung around for visitors to the Apple Blossom Festival this year). The temperature and wetting data are current through Monday morning, May 2. Predicted weather conditions are shown for May 2-5. 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 and wetting, the risk column shows that fire blight infection is again possible with wetting tomorrow, May 3 (note red color in BHWTR column). Be aware that wetting can occur with a fruit thinning or other application. Streptomycin should be included in such applications on days when all infection criteria are met except wetting. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. With five consecutive days possible for infection Apr 24-28, we have seen the most sustained fire blight pressure since 2004, and some infection will be expected in commercial orchards. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.
The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a-e) and canker blight symptom appearance, respectively. The column labeled SBS is tracking the appearance of shoot blight symptoms. Some early blossom cluster symptoms might be starting to appear in orchards. We are now seeing blossom symptoms from experimental inoculations done at our AREC Apr 23. With this year’s disease pressure, you may want to consider applying the plant growth regulator, Apogee as a shoot blight suppressant. Optimum timing of the first Apogee application for this purpose is at petal fall on king bloom, and a suppressive effect would not be expected until 7-10 after Apogee application. Note that risks can increase quickly with unpredicted wetting and warmer than predicted temperatures. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. This graphic will not be updated until May 4. 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.
