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 still
have much susceptible bloom. Here is the prediction for trees with first bloom
open Apr 17-18, 2015. The temperature and rainfall data are current through
Thursday morning, Apr 30. Predicted weather conditions are shown for Apr 30-May
6. 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 moderate through May 1, but warmer weather this weekend and into
next week will increase risk to where only wetting is lacking for infection to
be predicted for May 4-5, and with wetting, infection is predicted for May 6. (Be
aware that routine spray applications can provide enough wetting to meet the
wetting requirement for infection if all other infection conditions have been
met). In high-risk situations, a protective streptomycin application is
recommended ahead of predicted infection. Under the warmer temperature
conditions shown for next week, streptomycin will remain residually effective
for only about 3 days.
The BBS
column is tracking predicted appearance of blossom blight symptoms from
infection that occurred Apr 20, and this is predicted for May 6. 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 1. 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 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.
