Fire blight update

CAUTION: The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment only for the immediate area of the Virginia Tech AREC located six miles southwest of Winchester. Use of the information reported here for making orchard management decisions outside of that area is not our intent. Fruit producers outside of that area are encouraged to consult their state extension specialists for information similar to that provided here.

(Click on image to enlarge)

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Some cultivars still have some susceptible late bloom. Here is a prediction for trees with lingering bloom. (A month ago, who would have thought that we would see any bloom at Shenandoah Apple Blossom Festival time next weekend?). The temperature and wetting data were current through yesterday afternoon, Apr 27. Predicted weather conditions are shown for Apr 28-May 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). The risk column shows that fire blight infection could have occurred with wetting by dew Apr 20, and with any wetting of late bloom by rain, a spray application, or heavy dew Apr 15-17. After a ten-day decline, risk could again increase to an infective level with wetting May 2-5. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection and with any spray applications of other materials. Be aware that risks can abruptly increase with unpredicted warmer temperatures and wetting. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 20) and canker blight symptom appearance, respectively. Those symptoms should begin to appear about May 6. The numbers represent percent of required degree hours for symptom appearance. 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.