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 apple cultivars have reached petal fall but some have scattered bloom, and Yorks and Romes are at late bloom. The temperature and wetting data are current through Friday morning, May 6. Predicted weather conditions are shown for May 6-9. 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). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Based on predicted temperatures and wetting, the risk column shows that, with slightly warmer than predicted temperatures and wetting, fire blight infection could occur today, May 6. Also, be aware that wetting can occur with a fruit thinning application. Streptomycin should be included in such applications if late bloom is present and all infection criteria are met except wetting. With five consecutive days possible for infection Apr 24-28, we have seen the most sustained fire blight pressure since 2004, and some infection will be expected in commercial orchards. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.
The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11 and later ones as a-f) and canker blight symptom appearance, respectively. Some early blossom cluster symptoms might be starting to appear in orchards. Flower cluster leaf infection was reported May 3 in central Virginia. With this year’s disease pressure, you may want to consider applying the plant growth regulator, Apogee as a shoot blight suppressant. 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. Growers are advised to be alert to changes in forecasts on a day to day basis and protect high-risk blocks through late bloom as needed. This graphic will be updated May 9. 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.
