Squash Vine Borer, Not Caterpillar, Causing Wilting: Blossom-End Rot Also Present

Missouri gardener (raised beds, first year): black caterpillar in squash vines (not white like borer descriptions). Symptoms: wilting, yellow granular frass. Also blossom-end rot on fruit.

Caterpillar found in squash vine

Expert Diagnosis

Caterpillar is not the primary problem. Symptoms = classic squash vine borer (white larva inside stem). Black caterpillar may be secondary or different species.

Borer Management

• Preventive: Row covers (Reemay) on seedlings; remove at flowering
• Stem wrapping: Aluminum foil at base
• Once borer inside → plant usually lost; fruit ripens off vine

Blossom-End Rot on Squash

Caused by inadequate pollination and/or excess water (not calcium deficiency like tomatoes).

• Hand-pollinate with Q-tip (male → female) within 1 day of female opening
• Attract bees: sunflowers, marigolds, cosmos
• Water deeply 1.5"/week (1–2x), not shallowly
• Mulch heavily
• Low-nitrogen, high-P/K fertilizer

Resource

Ohio State squash borer guide