Fire blight update

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.

Maryblyt graphic. Click to enlarge.

FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Many apple trees are now near full bloom, and more bloom will continue to open over the next several days. The temperature and rainfall data are current through Friday morning, April 22. Predicted weather conditions are shown for April 22-27. 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 predicted temperatures and wetting, the risk column shows that fire blight infection is possible with rainfall later today Apr 20 (note red color). For infection to be predicted, wetting must occur after the EIP (epiphytic infection potential) reaches 100 or higher. Following today’s cool temperatures risk will again begin to increase and reach an infective level if it rains any of the days, Apr 24-27. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection. An application tomorrow should protect nearly through this long high-risk period. This graphic will be updated April 25, or sooner if significant change warrants it. The BBS and CBS columns are tracking predicted blossom blight symptom (from infection Apr 11) and canker blight symptom appearance, respectively. Numbers in these columns represent percent of required degree hours leading to blossom symptom appearance Apr 26 and canker margin symptoms Apr 27. 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.