Upticks in powdery mildew last year, plus a mild winter (which allows the fungus to overwinter in buds) set the stage for powdery mildew (Fig.3). Early season rains kept things at bay, but the recent change to drier weather while leaves continue to grow sets the stage for this disease. Powdery mildew is active during dry periods above 50 degrees and below 90, but happiest on dry, mild, spring days. Keep an eye on the most susceptible varieties (Jonathan, Baldwin, Ginger Gold, Ida Red, Cortland, Rome, Stayman Winesap…). We saw an uptick of PM on our Honeycrisps last year, so keep an eye on them, too! Remember that captan and mancozeb are not effective for controlling this disease, but DMI fungicides (Frac 3: Rally, Topguard, Indar, Inspire), strobilurins (Frac 11: Flint, Sovran), and 11+7 premixes (Pristine, Merivon, Luna Sensation) all are, and will help with rust and scab, assuming resistance is not an issue! SDHIs (Frac 7: Aprovia, Fontelis) are effective on PM, rust and scab, as well.
Powdery mildew is a problem in dry springs, especially on susceptible varieties