Choanephora rot

How to tell choanephora rot from other vining vegetable issues

• White, then purplish-black fungal growth, covers the flowers.

• The blossom end of the squash is soft, rotted and covered with fluffy purplish-black fungal growth.

Biology

• The fungus Choanephora cucurbitarum causes choanephora rot.
• The fungus survives from season to season in crop debris and moves to new flowers by insects, splashing water or wind.
• Infection most commonly occurs on flowers, although the fungi can also infect through wounds on the fruit.
• Infected flowers are soft, rotten and quickly covered with first white, then purplish-black fungal growth. In female flowers, the infection progresses into the fruit and results in soft water rot of the blossom end of the squash.
• The fungus thrives in wet conditions.

Managing choanephora rot in the garden

Rotting of small summer squash fruit is often a result of poor pollination, especially for the first round of fruit the plant sets.

• Space plants far enough apart to provide enough air movement in the field to quickly dry flowers and fruit.
• Remove infected fruit immediately to prevent it from spreading to other fruit.
• Proper spacing at planting is important, a guide for proper spacing can be found in the UMN vining vegetable growing guide.

Managing choanephora on farms

• Rotate vegetables so two or more years pass before planting any member of the squash family in the same location.
• Use drip irrigation instead of overhead sprinklers if possible.
• Space plants to provide enough air movement in the field to quickly dry flowers and fruit.
• Raised plant beds and plastic or paper mulch may limit fruit contact with moist soil and reduce moisture in the lower plant canopy.
• Remove infected fruit immediately to prevent it from spreading to other fruit.
• Fungicides are ineffective against choanephora rot because new susceptible flowers open every day.