Squash Blossom Blight

Choanephora cucurbitarium, a common fungus

Also known as Whisker rot

Blossom blight on crookneck squash [Credit: Howard F. Schwartz, Colorado University, Bugwood.org]

Blossom blight on squash [Credit: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org]

Host Plants:

On Crops: Squash, cucumber, okra

Where Found:

Warm temperate climates with abundant rainfall in late summer

Description:

This unusual disease is also called whisker rot, because infected blossoms become covered with a white cottony mass that develops black whiskers, which are the pin-like fruiting structures of the fungus. The fungus grows on the flower petals. It is most active when weather conditions are very damp and temperatures exceed 75F (24C).

Damage:

If the wet weather ends and you gently pull the infected blossom away, the young squash fruit may be worth saving if its blossom end has not darkened with rot. Prune off shriveled fruits attached to infected blossoms.

Preventing Problems:

Grow squash at wide spacing, so that the leaves of neighboring plants barely overlap. After the soil has warmed in summer, mulch beneath plants to create a barrier between the soil and the plants' foliage. After the plants begin blooming, use soaker hoses instead of sprinklers to water thirsty plants.

Managing Outbreaks:

Harvest affected fruits when they are small, because wet weather can cause the blossom end of the fruit to start rotting. Clear away weeds and tattered leaves that may slow the drying of squash blossoms after summer rains.

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