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. Most cultivars are now near full bloom. Here is the prediction for trees with first bloom open Apr 17-18, 2015. The temperature and rainfall data are current through Monday morning, Apr 27. Predicted weather conditions are shown for Apr 27-May 4. 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 recorded temperatures and wetting, the risk column shows that fire blight infection was possible Apr 20 and would have been possible with slightly warmer average temperatures for Apr 19 and 21. For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Based on predicted temperatures, risk will remain low-moderate through May 1, but warmer weather for the coming weekend will increase risk to where only wetting is lacking for infection to be predicted for May 3-4. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.
The CBS column at the right in the graphic indicates progression toward the appearance of canker margin symptoms due to extension of overwintering cankers from last year, with 100% of the degree hour requirement by May 2. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will signal build-up of inoculum which could become a factor in the event of a trauma blight situation due to hail injury, etc. The BBS column is tracking predicted appearance of blossom blight symptoms from the predicted infection Apr 20, with 64% of the degree hour requirement for predicted symptom appearance by May 4.