Managing Wet Rot (Choanephora) in Summer Squash

Recognizing Choanephora Wet Rot

A fuzzy, spongy mold covering summer squash fruit—starting at the blossom end and spreading, with black-tipped fibers—is characteristic of Choanephora fruit rot, commonly called wet rot. This fungal disease thrives in damp conditions with poor air circulation.

Immediate Actions

• Remove and destroy all infected fruit and blossoms to limit spore spread.
• Apply a copper-based fungicide every 7 days until conditions improve. Copper is effective against Choanephora and approved for edible crops.

Cultural Controls for Long-Term Prevention

Spacing and Airflow

Plant squash at least 2 feet apart. Wider spacing promotes leaf drying and reduces humidity around fruit.

Crop Rotation

Avoid planting cucurbits (squash, cucumbers, melons) in the same spot for 2–3 years. Rotate to unrelated crops like beans, corn, or tomatoes to break disease cycles.

Soil Improvement

Amend heavy, damp soil with generous organic matter—compost, aged manure, peat moss, shredded leaves, or grass clippings—to improve drainage. Mulch with straw or shredded leaves to reduce soil splash and conserve moisture evenly.

Water Management

Water deeply but infrequently—about 1.5 inches per week during dry spells. Avoid overhead irrigation; use drip or soaker hoses to keep foliage dry.

Slug Note

The mentioned slug issue on cucumbers is separate but also favors damp conditions. Iron phosphate baits or beer traps can help manage slugs without harming beneficial organisms.