NOTE: 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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| (Click to enlarge the graphic). |
FIRE BLIGHT:
Above is a cropped graphic from the Maryblyt 7 program. We will use Wednesday, Apr
5 as the date of first bloom open on Idared cultivar. The temperature and
rainfall data are current through Wednesday evening, April 5. Predicted weather
conditions are shown for April 6-11. 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 shows high
risk for Apr 5, but EIP was only 18, and had not yet reached the 100 level
required for infection. There were occasional blossoms open at our AREC as
early as Apr 3 or 4, but with the indicated temperatures, that would have made
little difference in the risk interpretation for Apr 6. With cooler predicted
temperatures through Apr 9, fire blight risk should remain low to moderate. However,
with warmer predicted temperatures Apr 10-11, the EIP would reach 78 by Apr 11.
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 Friday,
Apr 7.
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 the site is accessed. Cougarblight shows color-coded risk assessment as “Cougarblight 4-Day
DH” which remains low through Apr 9, then increases to high by Apr 11 when the
EIP reaches 77, comparable to the value of 78 shown for Maryblyt.
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| (Click to enlarge the graphic). |
For further discussion about fire blight risk assessment using Cougarblight, see the notes under "Disease management" under the graphic on the web site.
