Heavy apple scab and rust infection period Apr 12-13

In Winchester, we recorded a heavy apple scab and rust infection period Apr 12-13: 22 hr at 60°, with 0.77 inches of rain. Many cedar-apple rust and quince rust spores were released during this extended wetting period, and flowers are near their peak susceptibility for quince rust infection. In areas where there is a concern for rust infection, include an SI (DMI) fungicide in the next spray application. More wetting at warm temperatures is expected Apr 14-15. 

Apple scab infection conditions were similar to Winchester's southward in the Shenandoah Valley and east of the Blue Ridge to Central Virginia, but with slightly warmer temperatures and up to 1.8 inches of rain in some areas-- enough to erode the protective fungicide residue during the wetting event. 

Powdery mildew conidia have been available for infection at our AREC since Apr 6. Any “dry weather“ day above 53° is suitable for mildew infection. So far, we have had four mildew infection days.

The huge quince rust canker below seen recently in Frederick County has likely been producing rust basidiospores for 25 years or more. Its leaves were infected when it was only a couple years old and now it has a trunk diameter of 5-6 inches.

Sporulating quince rust canker on eastern red cedar. Photo by Mark Sutphin.