Scab and rust infection; heavy rainfall, May 15-16

We recorded 16 hours of wetting at 67-54° with 2.9 inches of rain at our AREC May 15-16. This was a secondary apple scab, cedar-apple rust infection period, and quince rust infection period, especially for later blooming cultivars. This amount of rainfall likely eliminated most of the protective fungicide residue on leaves and fruit, and puts more selective pressure on fungicides that are "at risk" for development of resistance in the apple scab fungus. 

Where protection was not adequate, growers are advised to follow up with a tank-mix of fungicides with multiple modes for scab, and an SI fungicide to offset possible infection of blossoms by quince rust. A protective fungicide should be included in this mix. Similar conditions occurred in central Virginia, where 4.2 inches of rainfall was recorded at Tyro.

Powdery mildew spores were available under the dry weather conditions favorable for infection Apr 9, and we have had 22 dry weather “mildew infection days” since Apr 9.

Fire blight: Predicted risk of fire blight has diminished for today through the weekend to May 20 when it will again increase to an infective level where lingering bloom remains.