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 all but the latest cultivars in bloom, and many approaching full bloom,
here is a prediction for trees with first bloom open last Friday, April 17,
2015. The temperature and rainfall data are current through Monday evening,
April 20. Predicted weather conditions are shown for April 21-24. 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 was
possible for Apr 20 and would also be possible with slightly higher than predicted temperatures Apr 21. For infection to be predicted, wetting must occur
after the EIP (epiphytic infection potential) reaches 100 or higher. Infection is more likely in areas where bloom
is more advanced, and temperatures warmer than those shown for Apr 19-21, and
if wetting occurs. In high-risk situations, a protective streptomycin application
is recommended ahead of predicted infection.
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. Be aware that risk can change quickly with
unpredicted warmer temperatures and wetting.
Wetting last night Apr 19-20 was enough for scab and rust infection: 15 hr wetting at 67-50 F with 1.12 in. of rain.
