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| King bloom on Idared, Apr 14, 2019. |
NOTE: This year for fire blight risk assessment, we will again
compare posted 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. We thank Dr. Mizuho Nita for hosting the Maryblyt 7.1 download
site at: http://grapepathology.org/maryblyt
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 14, 2019. Click to enlarge. |
FIRE BLIGHT: Above is a cropped
graphic from the Maryblyt 7 program. We will use Saturday, Apr 13 as the date
of first bloom open on early cultivars such as Idared and Pink Lady. The
temperature and rainfall data are current through Sunday evening, April 14.
Predicted weather conditions are shown for April 15-20. 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, and this must coincide with an average daily temperature
of 60°F or more. Based on recorded temperatures and wetting, the risk
column shows high risk for Apr 13, 15, and 16, but lacks the required EIP of 100. Entering an earlier bloom date did not raise the EIP for Apr 13, and did not raise
the risk of infection. With cooler predicted
temperatures mid- week, fire blight risk should be low to
moderate Apr 17-18. However, with warmer than predicted temperatures, expect the risk to
increase again.
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 assessment as “Cougarblight 4-Day DH” risk is low for Apr 14-16.
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| Graphic from Cougarblight, April 14, 2019. Click to enlarge. |
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. The fire blight
outlook will be updated Apr 17.
