Disease update: Fire blight risk high; apple scab lesions present

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. At our AREC most apple cultivars still have susceptible bloom, some are near full bloom and some have late bloom continuing to open. Later cultivars such as Rome Beauty are not yet at full bloom. 

FIRE BLIGHT: Above is a graphic from the Maryblyt 7 program. The temperature and rainfall data are current through this morning,  May 5. Predicted weather conditions are shown for May 5-14. 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 predicted temperatures and wetting, the risk column shows that fire blight risk will be high, lacking only wetting for infection, for May 8-10 and with predicted wetting, infection conditions are likely May 11-14. In high-risk situations, a protective streptomycin application is recommended ahead of predicted infection conditions, or with applications that cause wetting when all other infection conditions have been met. This graphic will be updated May 7. 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.

APPLE SCAB: Scab lesions, as shown below, were present at our AREC on May 2. As is quite common with appearance of the earliest primary scab, lesions may be somewhat obscured by necrotic frost injury which seemed to target the scab lesion. 

Primary scab lesion on Gala flower cluster leaf at right.

Lower leaf surface- note sporulation
outside of necrotic area

Primary scab symptom- necrotic area from
 frost injury on upper leaf surface

The abundance of conidiospores on the lesion indicated that they were likely present through last week's heavy infection period and would have contributed to heavy secondary infection on unprotected trees.