Wet Weather Raises Risk of Apple Storage Diseases

By Blake Jackson

Apple growers should remain vigilant as harvest approaches, especially following periods of wet weather that can increase the risk of storage diseases.

According to Kari A. Peter, Associate Research Professor at Penn State Extension, fungi responsible for fruit rots and apple scab can infect fruit late in the season and remain undetected until months later in storage.

While apple scab is often considered an early-season disease, prolonged wet conditions can lead to late-season infections. Similarly, fungal pathogens that cause storage rots may infect fruit in the orchard when favorable environmental conditions are present.

As a result, apples that appear healthy at harvest can later develop scab lesions or fruit rot during storage.

Growers are encouraged not to extend the interval between their final fungicide application and harvest, particularly if fruit will be stored for more than a month.

Research indicates that troublesome storage diseases, such as Alternaria rot and Bull’s-eye rot, often begin with infections in the orchard.

Although captan remains an effective preharvest fungicide, heavy rainfall can reduce its effectiveness by washing residues from fruit surfaces. More durable fungicides may provide better protection before harvest.

Organic growers can utilize sulfur, Oso, and bacterial-based products such as Serenade and Double Nickel for short-term disease management.

Storage rots can also create entry points for blue mold, caused by Penicillium species. This disease develops only during storage and can produce patulin, a regulated mycotoxin that may cause fruit loads to be rejected by processors if contamination levels are too high.

Additional management practices include harvesting fruit at proper maturity, handling fruit carefully to prevent bruising, removing rotten apples from trees, using clean bins, minimizing soil contamination, cooling fruit quickly after harvest, and reducing the time between harvest and delivery to storage or packing facilities.

By combining orchard disease management with careful harvest and storage practices, growers can significantly reduce losses and maintain fruit quality throughout storage.

FAQs

• Why are apple storage diseases more common after rainy weather?

Wet conditions favor fungal infections and can wash protective fungicides off fruit.

• Can apples look healthy at harvest and still develop rot later?

Yes, latent infections may not appear until fruit is in storage.

• What are the most common storage rots in apples?

Alternaria rot, Bull’s-eye rot, and blue mold are among the most significant storage diseases.

• Why is blue mold a concern for apple growers?

Blue mold can produce patulin, a regulated mycotoxin that may lead to crop rejection.

• How can growers reduce storage risk before harvest?

Apply effective preharvest fungicides and maintain recommended spray intervals.

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