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. With some apple trees at petal fall but many still with much susceptible bloom, here is a prediction for trees with first bloom open Monday, Apr 5. The temperature and rainfall data are current through Monday morning, Apr 19. Predicted weather conditions are shown for Apr 19-22. 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). The risk column show that infection was possible as predicted Friday. BBS column shows that we have only reached 55% of the requirement for predicted blossom blight symptoms tracked from the Apr 8 infection. Risk is reduced through Apr 22, as shown, due to cool weather (and actually on into next week with the current extended forecast). As always, be aware that risks can increase quickly with warmer than predicted temperatures and unpredicted wetting, and protect high-risk blocks through late bloom as needed. 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.
OTHER DISEASES: Very intermittent wetting totaling only 0.02 inches of rain Apr 16-17 probably did not result in apple scab or rust infection, especially where protectants against these diseases were applied last week. If you are in a quince rust-prone area and did not have adequate rust protection, it may be wise to include an SI (sterol-inhibiting) fungicide for after-infection rust control in your next application.
Meanwhile, all of these dry days continue to favor secondary powdery mildew infection.
