Pennsylvania Apple Growers Face Early Spring Risks

By Blake Jackson

Unseasonable swings between winter chill and summer-like warmth are shaping early spring conditions across Pennsylvania, creating challenges for apple growers.

According to Kari A. Peter, Associate Research Professor at Penn State Extension, the warm spell from March 8 to 12 encouraged many apple trees in the southern part of the state to break dormancy earlier than usual. Green tip development followed between March 17 and 22, depending on the variety.

Once trees exit dormancy, the risk of apple scab becomes immediate. Spores that survived the winter in fallen leaves are ready to infect new growth. Rainfall on March 26 and 27 likely triggered the first infection period of the season.

Growers who applied a dormant copper spray beforehand would have had effective protection during this event.

Looking ahead, favorable weather conditions are expected to accelerate bud development across the region.

Additional infection periods are possible around April 1 and 2, with further risk between April 3 and 5 as forecasts indicate a strong likelihood of rain. Monitoring local conditions closely remains essential.

During the half-inch green tip stage, protective strategies include applying rainfast mancozeb alone or in combination with products such as Syllit or micronized sulfur. Organic growers can rely on potassium bicarbonate or sulfur as viable options.

As trees progress to the tight cluster stage, warmer temperatures between 70°F and 80°F may speed up growth, requiring adjustments in disease management.

Fungicides such as Axios, Cevya, Indar, Inspire Super, Procure, Scala, and Vangard can be combined with mancozeb for improved control.

However, growers are advised to avoid FRAC Group 7 products at this time and reserve them for later in the season when disease pressure intensifies.

Powdery mildew also becomes a concern during tight cluster, particularly under dry, humid conditions. Effective management includes tank mixing mancozeb with targeted fungicides or using sulfur-based and potassium bicarbonate treatments in organic systems.

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