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.
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. With most apple orchards near full bloom, here is a prediction for trees with first bloom open Monday, Apr 5, 2010. The temperature and rainfall data are current through Monday morning, Apr 12. Predicted weather conditions are shown for Apr 12-16. 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 occurred as predicted earlier with storms Apr 8. The wind-driven rains made it likely that bacteria would have spread throughout an orchard from blossoms that were open earlier to ones that had opened just before the rain. For infection to be predicted, wetting has to occur when the EIP (epiphytic infection potential) reaches 100 or higher, and this level had reached 4X that threshold Apr 7. Currently, cooler temperatures are expected to reduce the fire blight threat through Apr 14, but the risk will again increase with warmer temperatures Apr 15-16 and possible showers Apr 16. Be aware that risks can increase quickly with warmer temperatures and unpredicted wetting. The Maryblyt graphic will be updated Apr 14 or sooner. 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.
