Recent rainfall across Wisconsin has provided much-needed moisture for crops, but it has also created favorable conditions for several important strawberry diseases. As growers move through harvest, periods of prolonged leaf wetness, high humidity, and frequent rain events can increase losses from fruit rots while also setting the stage for foliar and crown diseases later in the season.

Regular scouting and timely management are especially important during wet periods because disease can develop rapidly and spread quickly through fields.

Common Strawberry Diseases in Wisconsin

Gray Mold

Gray mold, caused by Botrytis cinerea, is often the most significant disease concern during harvest. The pathogen infects flowers during bloom and can remain latent until fruit begin to ripen. Warm temperatures combined with extended periods of moisture can result in rapid disease development. Symptoms begin as soft, light brown lesions that quickly become covered with the characteristic gray, fuzzy fungal growth. Infected berries can spread disease to healthy fruit during harvest, handling, and storage.

To reduce losses:

• Harvest frequently and remove overripe fruit.
• Remove diseased berries from the planting whenever practical.
• Promote air movement through the canopy.
• Avoid overhead irrigation during harvest when possible.
• Maintain fungicide coverage during extended wet periods if harvest intervals allow.

Anthracnose Fruit Rot

Anthracnose fruit rot, caused by Colletotrichum species, can be particularly problematic during warm, rainy weather. The disease often appears suddenly, with berries developing firm, sunken lesions that may produce salmon-colored spore masses under humid conditions. Splashing rain can rapidly move spores throughout a field, and infections often increase dramatically following periods of frequent rainfall. Growers should pay close attention to fields with a history of anthracnose, as the pathogen can survive on infected plant material and nursery stock.

Leather Rot

Leather rot, although less common in some years, can become significant when fruit are exposed to prolonged soil moisture and repeated rainfall events.

Symptoms include:

• Firm berries with a leathery texture
• White, pink, or purple discoloration
• Fruit that remain tough rather than soft and decayed

Fruit touching wet soil or mulch are particularly vulnerable. Good drainage and mulch management help reduce disease pressure.

Angular Leaf Spot

Wet weather also favors angular leaf spot, a bacterial disease that can develop rapidly during periods of prolonged moisture.

Symptoms include:

• Water-soaked lesions on leaves
• Angular spots limited by leaf veins
• Bacterial ooze that may be visible under humid conditions
• Calyx infections on fruit

Because this disease is bacterial, fungicides are ineffective. Management relies on sanitation, reducing leaf wetness, and starting with clean planting material.

Post-Harvest Considerations: Foliar and Crown Diseases

Heavy rains during harvest can also create favorable conditions for diseases that impact plant health later in the season.

Growers should continue scouting for:

• Common leaf spot
• Leaf scorch
• Leaf blight
• Phytophthora crown and root rot

These diseases can reduce plant vigor, weaken crowns, and ultimately affect next year’s yield potential. Fields with standing water or poorly drained areas should be monitored carefully for Phytophthora symptoms, including plant collapse, wilting, and reddish-brown crown discoloration.

Fungicides

For conventional growers, fungicide programs should focus on protecting healthy flowers and fruit before infection occurs. Materials commonly used for Botrytis and anthracnose management include products such as:

• Switch (FRAC 9 + FRAC 12)
• Pristine (FRAC 7 + FRAC 11)
• Miravis Prime (FRAC 7 + FRAC 12)
• Captan
• Thiram (where labeled)

Resistance management remains critical. Rotate FRAC groups and avoid repeated applications of products with the same mode of action.

Organic Management of Strawberry Diseases

Organic growers have fewer options and should focus heavily on prevention.

Products that may provide suppression include:

• Biological fungicides containing Bacillus species
• Biological products containing Aureobasidium pullulans (primarily for Botrytis)
• Copper products (watch for phytotoxicity)

These materials generally provide the greatest benefit when applied preventatively and integrated with cultural practices such as sanitation, frequent harvest, canopy management, and good drainage.

In Summary

The recent rainfall has increased disease risk in many strawberry plantings. Frequent harvest, removal of diseased fruit, improved air movement, and maintaining appropriate fungicide protection are key strategies for minimizing losses.

While fruit rots are the most immediate concern during harvest, growers should also be mindful of crown and foliar diseases that may impact plant health and productivity later in the season. Continued scouting over the coming weeks will help identify problems early and improve management success.

Additional Reading

• Fungal Foliar Diseases of Strawberry
• Root and Crown Rot Diseases on the Rise in Wisconsin Strawberries