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 scattered bloom and later blooming cultivars have much susceptible bloom.
FIRE BLIGHT ALERT: The risk column of Maryblyt 7 graphic below, based on predicted temperatures and wetting for May 12-16, shows that fire blight risk will remain extremely high wherever bloom is present this week. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions. 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 this week, streptomycin remains residually effective for only about 3 days.
With this fire blight pressure, 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, and a suppressive effect should not be expected until 7-10 after Apogee application.
The temperature and rainfall data are current through Monday morning, May 12, for the graphic above from the Maryblyt 7 program. Predicted weather conditions are shown for May 12-16. 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 symptom appearance (104a) May 14. 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 14. Canker advancement cannot 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 14. 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.
RUSTS: Today we observed scattered cedar-apple lesions on unprotected, frost-injured leaves from the infection period Apr 14-15, and many developing lesions from the long wetting period Apr 28- May 1. That infection period will also likely result in quince rust on unprotected fruit as the fruit begin to grow.
