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.
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| Graphic from Maryblyt 7, April 24, 2019. Click to enlarge. |
FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. Apple trees are near full bloom in the Winchester area. The temperature and rainfall data are current through Tuesday night, April 23. Predicted weather conditions are shown for April 24-28. 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, and this must coincide with an average daily temperature of 60°F or more. Based on recorded temperatures and wetting, the risk column shows the infection was possible Apr 19 and 25, and would be possible with wetting Apr 18, 23 and 24. Streptomycin is recommended to be applied today or tomorrow, Apr 24 or 25, and for any regular spray application when wetting is the only factor lacking for infection. Also, remember to protect young and recently planted trees, which have flowers but might be considered to be "non-bearing". Fire blight risk should subside with cooler predicted temperatures Apr 26-28. The BBS column is tracking the appearance of blossom blight symptoms from infection that occurred Apr 19. Symptom appearance is predicted when this value reaches 100.
Below is the graphic from the Cougarblight model as shown on our NEWA site. We selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/13/2019. Cougarblight shows color-coded risk assessments as “Cougarblight 4-Day DH” and infection potential EIP value. This risk is "high" for Apr 23, 24 and 26 and "extreme" or infection tomorrow, Apr 25, and also with infection possible with a trace of wetting from rainfall today, Apr 24, so the current predictions are similar for the Cougarblight and Maryblyt models.
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| Graphic from the NEWA/Cougarblight model, April 24, 2019. Click to enlarge. |
Note that real fire blight risks can change quickly with warmer than predicted temperatures and wetting. In high-risk situations, a streptomycin application is more effective when applied ahead of predicted infection.
