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. Susceptible flowers are
still open on most cultivars. Here is the prediction for trees with first bloom
open Monday, April 11, 2016. The temperature and rainfall data are current
through Wednesday morning, April 27. Predicted weather conditions are shown for
April 27-May 1. 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). For infection to be predicted, wetting must occur after the EIP
(epiphytic infection potential) reaches 100 or higher, which has been true
since Apr 18. Based on predicted temperatures, the risk column shows infection
conditions for Apr 21-22 and 24-27. (Note that the outlook for Apr 25-26 changed
from the previous post due to unpredicted showers both days). For optimum
control, a protective streptomycin application is recommended ahead of
predicted infection, but it can also provide about one day after-infection
suppression. Predicted cooler conditions after today and through APPLE BLOSSOM
FESTIVAL weekend should reduce risks during this time. (The cooler temperatures
will probably also ensure that a few apple blossoms will be present through the
weekend for those who come to the area looking for them).
The BBS column
is tracking predicted symptom development for the first infection Apr 21. Yesterday
we could already see symptoms from experimental inoculations Apr 18. The CBS
column predicted for the appearance of canker margin symptoms Apr 26, due to
extension of overwintering cankers from last year, and it is now tracking the predicted
appearance of canker blight symptoms when that value reaches 100. Canker blight
cannot be prevented by chemical treatment and the presence of symptoms would
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 WeatherChannel for Winchester, supplemented by site-specific data from SkyBit Inc. Be
aware that risk can change quickly with unpredicted warmer temperatures and
wetting. Unless the outlook changes appreciably form currently predicted
conditions, the fire blight outlook will not be updated until Monday, May 2.
