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 cultivars are now near
full bloom. Here is the prediction for trees with first bloom open Apr 17-18,
2015. The temperature and rainfall data are current through Monday morning, Apr
27. Predicted weather conditions are shown for Apr 27-May 4. 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 recorded temperatures
and wetting, the risk column shows that fire blight infection was possible Apr
20 and would have been possible with slightly warmer average temperatures for Apr
19 and 21. For infection to be predicted, wetting must occur after the EIP
(epiphytic infection potential) reaches 100 or higher. Based on predicted temperatures, risk will
remain low-moderate through May 1, but warmer weather for the coming weekend
will increase risk to where only wetting is lacking for infection to be predicted
for May 3-4. In high-risk situations, a protective streptomycin application is
recommended ahead of predicted infection.
The CBS
column at the right in the graphic indicates progression toward the appearance
of canker margin symptoms due to extension of overwintering cankers from last
year, with 100% of the degree hour requirement by May 2. Canker advancement
cannot be prevented by chemical treatment at this time and the presence of
symptoms will signal build-up of inoculum which could become a factor in the
event of a trauma blight situation due to hail injury, etc. The BBS column is
tracking predicted appearance of blossom blight symptoms from the predicted
infection Apr 20, with 64% of the degree hour requirement for predicted symptom
appearance by May 4.
The weather
conditions used in the predictive part of this graphic come from the WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be
aware that risk can change quickly with unpredicted warmer temperatures and
wetting.
