The observations, conditions, and recommendations reported for Winchester, VA are provided as a guide to fire blight risk assessment for the area of the Virginia Tech AREC located six miles southwest of Winchester. At our AREC most apple cultivars still have some susceptible bloom and later blooming cultivars are near full bloom.
FIRE BLIGHT ALERT: The risk column of Maryblyt 7 graphic below, based on predicted temperatures and wetting for May 9-14, shows that fire blight risk will remain extremely high for the next week May 8-15 (and later). In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions. Remember that routine spray applications can provide enough wetting to meet the wetting requirement for infection if all other infection conditions have been met. Under the warm temperature conditions shown for the next week, streptomycin remains residually effective for only about 3 days.
With fire blight pressure looming, you may want to consider applying the plant growth regulator, Apogee to suppress shoot blight if hail or another trauma blight event were to occur. Optimum timing of the first Apogee application for this purpose is at petal fall on king bloom, but a suppressive effect should not be expected until 7-10 after Apogee application.
The temperature and rainfall data are current through Friday morning, May 9, for the graphic above from the Maryblyt 7 program. Predicted weather conditions are shown for May 9-15. The components of fire blight risk are indicated in the columns labeled B (blossoms open), H (degree hours for epiphytic bacterial population buildup, EIP >100), W (wetting by rain or dew), and T (average daily temperature 60 F or above).
The BBS column is tracking predicted appearance of blossom blight symptoms from infection May 8 to predicted symptoms (105a) May 15. The CBS column at the right in the graphic indicates progression toward the appearance of canker blight symptoms on new growth, due to extension of overwintering cankers from last year, with canker margin symptoms (CMS) by May 8 and canker blight symptoms May 15. Canker advancement will not be prevented by a chemical treatment, 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.
This graphic will be updated May 12. 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.
