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 trees at or beyond petal fall but others with susceptible bloom that will likely persist through the weekend, here is a prediction for areas where bloom was first open Apr 5, 2010. The temperature and wetting data are current through Thursday morning, Apr 29. Predicted weather conditions are shown for Apr 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). The risk column shows that infection could have occurred Apr 16 and Apr 8 (not shown). With the return of warm weather for Festival Weekend, risk will again increase to an infective level if there is any wetting of susceptible late bloom tomorrow and into next week. “Wetting” can occur with a thinning or maintenance spray and inclusion of streptomycin with such sprays is advised. Wetting and infection can also occur with heavy dew. BBS column, tracking the Apr 8 and Apr 16 infections, shows that the blossom blight symptoms from these two infections will begin to appear Apr 30-May 2. (Blossom blight was observed yesterday in Rappahannock County). Canker blight symptoms (CBS), resulting from the extension of overwintering cankers to involve new growth will also appear in the next few days. Continue to protect high-risk blocks through late bloom as needed. 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.
