Fire blight update April 23

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. All cultivars are now in bloom and most of them are near full bloom. Here is the prediction for trees with first bloom open last Friday or Saturday, April 17-18, 2015. The temperature and rainfall data are current through Thursday morning, April 23. Predicted weather conditions are shown for April 23-27. 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.  Infection for Apr 19-21 would have been more likely in areas where bloom is more advanced, and temperatures warmer than those shown, and if wetting also occurred Apr 19 and 21. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. Based on predicted temperatures, risk should now remain low to moderate through Apr 27 (and well into next week).

The CBS column at the right in the graphic indicates progression toward the appearance of canker margin symptoms on new growth, due to extension of overwintering cankers from last year, 89% of the degree hour requirement by Apr 27. Canker advancement cannot be prevented by chemical treatment at this time and the presence of symptoms will indicate a 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 infection Apr 20, now with only 12% of the degree hour requirement for predicted symptom appearance, which will be much delayed with cooler weather into next week. 

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. Be aware that risk can change quickly with unpredicted warmer temperatures and wetting.