Timing Fungicide Applications for Apple Scab in Unusual Weather

An arborist in Michigan faces an early warm spell (70–80°F in March) with apple scab already active. Past June and September sprays caused temporary leaf droop. With many new clients, he needs to prioritize sites and understand temperature triggers.

Use MSU Enviro-weather

Michigan State University's Enviro-weather system provides site-specific disease forecasting based on decades of research. Select the nearest weather station, then choose Fruit → Apple → Apple Scab to see real-time risk levels (e.g., "light" risk with symptom prediction dates). This helps target sprays only where needed.

Temperature & Wetness Thresholds

The MSU Apple Scab page includes a table of required temperatures and leaf-wetness periods for infection. This answers the general question about temperature shifts. Remember that low-lying, fog-prone sites may have higher risk than the station indicates.