Scab and rust infection period

A scab and rust infection period ended Monday morning, May 3: 11 hr, 72 deg., 0.4 in. rain. Heavy secondary/primary apple scab from the April 14 infection period is now evident on unprotected shoot leaves. Consider options for stronger "catch-up" treatments if your orchard was not properly covered for the earlier infection periods March 28 and Apr 14 or the more recent ones which could result in damaging secondary fruit infection, Apr 24-25, Apr 25-27, and May 2-3.

Secondary mildew infection is also apparent from ongoing infections which occurred on at least 21 days in April.

Apple Blossom Festival weekend temperatures were actually slightly warmer than those indicated as predicted below, resulting in possible fire blight infection on late bloom wherever wetting occurred. The warmer temperatures should also bring earlier than predicted blossom blight symptom development this week.

For purposes of monitoring cumulative wetting hours for sooty blotch and flyspeck development, we are using Apr 19 as petal fall and wetting hour accumulation of wetting hours begins 10 days later, Apr 29. So far we have accumulated 11 hours toward the 250-hr threshold. 

Disease situation

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. With most cultivars near full bloom and all with some bloom open, here is a prediction for trees with first bloom open Monday, April 5, 2010. The temperature and rainfall data are current through Friday morning, April 9. Predicted weather conditions are shown for April 9-12. 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). The risk column shows that fire blight infection occurred as predicted with storms with strong winds yesterday afternoon. The wind-driven rains made it likely that bacteria would have spread throughout an orchard from blossoms that were open earlier to ones that had opened just before the rain. For infection to be predicted, wetting has to occur after the EIP (epiphytic infection potential) reaches 100 or higher, and this level had reached 4X that threshold.  Cooler temperatures will reduce the fire blight threat through the weekend. The Maryblyt graphic will be updated April 12 or earlier if it changes dramatically. 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.

Other diseases:
Yesterday's 10-hr wetting from 4 PM to 2 AM this morning was not quite long for apple scab infection, and cedar-apple rust spores were not released. Predicted dry weather through most of next week will again favor powdery mildew infection.