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. Early bloom is now open on many apple 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 13. Predicted weather conditions are shown for April 13-20. 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.
Based on record temperatures and wetting, the
risk column shows high risk for Apr 11, but the EIP had not yet reached 100 and
would have required max/min temperatures 9 degrees warmer to reach the infective level.
There were occasional blossoms open at our AREC as early as Apr 8, but with the
indicated temperatures, that would have made little difference in the risk
interpretation for Apr 11. With cooler predicted temperatures through the rest
of this week, fire blight risk should remain low to moderate. However, with
warmer predicted temperatures Apr 17-18, the EIP would again approach the
infective level by Apr 18.
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. In high-risk situations, a protective streptomycin application is
recommended ahead of predicted infection. This fire blight outlook will be
updated Friday, April 15.
FUNGAL DISEASES: Powdery mildew remains our most active early season apple disease, with 13 dry weather mildew infection days recorded since March 16. Primary and secondary mildew infection will likely become more evident after we get some consistently warmer growth conditions.
