Wednesday, April 27, 2016

Fire blight infection conditions today

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.