NOTE: This year for fire
blight risk assessment, we are comparing graphics from Maryblyt 7 and from the
Cougarblight model as shown on our NEWA site. We are using the same
weather data from our NEWA station to make these
comparisons in both predictive programs.
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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| Maryblyt graphic May 1, 2017. Click to enlarge. |
FIRE BLIGHT:
Above is a cropped graphic from the Maryblyt 7 program, using Apr 5 as the date
for first bloom open on Idared cultivar. Some early cultivars still have scattered
susceptible bloom, while later cultivars are beyond petal fall but still with susceptible
bloom in the Winchester and central Virginia areas. Some recently planted trees
still have much susceptible bloom. The temperature and rainfall data are
current through Sunday evening, Apr 30. Predicted weather conditions are shown
for May 1-5. 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 and possible infection with
any wetting Apr 11-12, 15-18, 21 and, and if bloom persists, Apr 27-May 2.
Infection was indicated for Apr 12, 15-17 21 and Apr 28-30. Predicted warming
temperatures have again increased risk wherever susceptible bloom remains through
May 2, then declines with cooler temperatures through May 5. Note that risk can
change quickly with warmer than predicted temperatures and wetting. Continue to
protect late bloom and open bloom on recently planted trees as needed.
The BBS column is tracking predicted
symptom development for the first infection Apr 12 and symptoms are predicted
to appear Apr 27. Later infections are tracked with letters b-e, and symptoms
for those are predicted to appear Apr 28-May 2. The CBS column indicates
progression toward the appearance of canker margin symptoms due to extension of
overwintering cankers from last year, which were predicted to Apr 22. Canker
advancement cannot be prevented by chemical treatment at this time and the
presence of symptoms will signal build-up of inoculum which could become a
factor in the event of a trauma blight/shoot blight situation due to hail
injury, etc. To offset the potential for
shoot tip infection in an active fire blight year such as this one, apply the
plant growth regulator, prohexadione-calcium (Apogee, Kudos), at late bloom.
Shoot blight suppression results from hardening off of vegetative shoot growth
starting about 10 days after the initial application.
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| Cougarblight graphic May 1, 2017. Click to enlarge. |
