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.
APPLE SCAB lesions resulting from infection periods during the period March 26 to Apr 7 may be present in poorly protected orchards, and extended wetting could result in heavy secondary infection this week, Apr 24-26.
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| Maryblyt graphic for Winchester, Apr 24, 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. Many trees still have some
susceptible bloom in the Winchester
area. The temperature and rainfall data are current through Sunday evening, Apr
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. Based on recorded temperatures and wetting, the
risk column shows high risk and possible infection with any wetting Apr 11-12,
15-18, and 21, and if bloom persists, Apr 27-28. Infection was indicated for
Apr 12, and 15-17 and is predicted with wetting Apr 21. Note 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. Predicted cooler temperatures should reduce risk
Apr 24-25, but will probably cause late bloom to persist, setting up higher
risk of infection of late bloom with warmer temperatures Apr 27-28. Continue to
protect late bloom and open bloom on young 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. The CBS column indicates progression toward the appearance of
canker margin symptoms due to extension of overwintering cankers from last
year, which would be predicted to occur after that value reached 100 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. The fire blight
outlook will be updated Wednesday, Apr 26.
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 as “extreme”
Apr 21, and “high” Apr 22-23 then declining Apr 24-26, but returning to high
and extreme Apr 27-28.
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| Cougarblight graphic for Winchester, Apr 24, 2017. Click to enlarge. |
