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.
FIRE BLIGHT:
Above is a cropped graphic from the Maryblyt 7 program. Many trees still have susceptible
bloom. Here is the prediction for trees with first bloom open Apr 17-18, 2015.
The temperature and rainfall data are current through Wednesday night, May 6.
Predicted weather conditions are shown for May 7-11. 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). Based on recorded temperatures and
wetting, the risk column shows that fire blight infection was possible Apr 20
and would have been possible with slightly warmer average temperatures for Apr
19 and 21. For infection to be predicted, wetting must occur after the EIP
(epiphytic infection potential) reaches 100 or higher.
Based on predicted temperatures, EIP will remain at an infective level through this weekend, requiring only wetting to trigger infection conditions wherever susceptible bloom is present. Wetting from rain occurred at the AREC May 5 and 6. Other forms of wetting capable of triggering infection conditions include heavy dew, fog or routine spray applications-- anything that can splash the fire blight bacteria from the flower stigma into the nectaries in the base of the flower. Infection conditions remain possible with wetting wherever bloom is present May 7-11. This situation generally applies to other areas in the mid-Atlantic region well beyond Winchester. It is recommended that streptomycin be included with routine spray applications in high risk situations this week. Under the temperature conditions shown for this week, expect streptomycin to remain residually effective for only about 3 days.
Based on predicted temperatures, EIP will remain at an infective level through this weekend, requiring only wetting to trigger infection conditions wherever susceptible bloom is present. Wetting from rain occurred at the AREC May 5 and 6. Other forms of wetting capable of triggering infection conditions include heavy dew, fog or routine spray applications-- anything that can splash the fire blight bacteria from the flower stigma into the nectaries in the base of the flower. Infection conditions remain possible with wetting wherever bloom is present May 7-11. This situation generally applies to other areas in the mid-Atlantic region well beyond Winchester. It is recommended that streptomycin be included with routine spray applications in high risk situations this week. Under the temperature conditions shown for this week, expect streptomycin to remain residually effective for only about 3 days.
The BBS
column is tracking predicted appearance of blossom blight symptoms from
infection that occurred Apr 20, and this is predicted for May 6. (Actually on
May 4 we saw early symptoms from test inoculations Apr 20). Yesterday, May 6, blossom
blight symptoms were observed in a Rappahannock County orchard, also likely
from Apr 20 infection. The CBS column at the right in the graphic indicates
progression toward the appearance of canker margin symptoms due to extension of
overwintering cankers, with 100% of the degree-hour requirement May 1. Canker
blight symptoms on new growth, due to extension of overwintering cankers are
predicted for May 8. Canker advancement cannot be prevented by treatment and
the presence of symptoms will signal build-up of inoculum which could become a
factor in the event of a trauma blight situation due to hail injury, etc. The weather conditions used in the predictive
part of this graphic come from the Weather Channel for Winchester, supplemented
by site-specific data from SkyBit Inc. Be aware that risk can change quickly
with unpredicted warmer temperatures and wetting.
Fungal diseases: Apple scab, quince rust, and cedar-apple rust infection periods occurred, with temperatures in the 60s, the nights of May 5 and 6. Blossoms are still susceptible to quince rust infection at petal fall.
Fungal diseases: Apple scab, quince rust, and cedar-apple rust infection periods occurred, with temperatures in the 60s, the nights of May 5 and 6. Blossoms are still susceptible to quince rust infection at petal fall.
