FIRE BLIGHT OUTLOOK: This year for fire blight risk assessment, we will be comparing and posting graphics from Maryblyt 7, as in previous years, and also from the Cougarblight model as shown on our NEWA site. We will be using the same weather data from our NEWA station to make these comparisons.
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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FIRE BLIGHT: Above is a cropped graphic from the Maryblyt 7 program. We are using Apr 5 as the date of first bloom open on Idared cultivar. The temperature and rainfall data are current through Friday evening, April 7. Predicted weather conditions are shown for April 8-12. 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 recorded temperatures and wetting, the risk column showed high risk for Apr 5, but EIP was only 18, not yet at the 100 level required for infection. With cooler predicted temperatures through Apr 9, fire blight risk should remain low. However, with warmer predicted temperatures Apr 10-12, the EIP would reach 111 and 126 for Apr 11 and 12, respectively. Based on predicted temperatures, the risk column shows high risk for Apr 11-12, with only wetting lacking as the trigger for fire blight infection these days. Be aware that in situations where all other requirements for infection have been met except wetting, wetting from a maintenance spray application can provide the wetting trigger for infection to occur. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection.
Below is the graphic from the Cougarblight model as shown on our NEWA site. Note that we selected orchard blight history option as “Fire blight occurred in your neighborhood last year” and first blossom open date as 4/5/2017. This date must be re-set each time this site is accessed. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day DH” which remains low through Apr 9, then increases to "Caution" Apr 10, and "High" by Apr 11 and 12 when the EIP reaches 106-114, comparable to the values of 111-126 shown for these dates in Maryblyt.
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Be aware that risk can change quickly with unpredicted warmer temperatures and wetting. The fire blight outlook will be updated Monday, Apr 10.
