Squash Vine Borer on Vegetables

Squash vine borer larva damaging a squash plant
photo: Jim Jasinski, Ohio State University Extension, Bugwood.org

Updated: June 28, 2024

Appearance

Eggs: tiny brown flattened ovals attached singly.
Larvae: wrinkly, white to cream color hairless caterpillar up to 1" with dark head.
Pupa: dark brown shiny with tapered ends. Cocoon: black, rough-textured.
Adult: fat, black clear-winged moth with orange legs and orange and black abdomen. Appears similar to a wasp.

Overwinters as pupa or pupa in cocoon 2" under soil. In May, moths can lay eggs three days after emergence.
Are active in daytime depositing eggs on all plants parts except upper leaf, but mostly on stems near plant base.
Mated female moths fly low and slow around plant. Upon hatching in early summer, larvae bore into stem to feed for up to 4 weeks. Often more than one present in an infested stem. When mature at 4-6 weeks, larvae exit vine and dig 1" into soil to pupate.
1-2 generations a year.

Summer and winter squash and pumpkin. Very rarely in cucumber, gourd, and melon.

Tunneling larvae push greenish white sawdust-like frass (excrement) out the entrance hole.
The stem area near the entrance hole(s) will feel mushy.
Plant's runner or entire vine wilts quickly from larval feeding within stem.
Wilting may occur first during daytime heat.
Entire plant dies if untreated.

Watch for moths hovering around plants mid-May to mid-June.
Inspect for eggs.
Put on a long-sleeve shirt and inspect base of vine for larvae entrance holes and frass.
Sudden wilting of a runner or entire vine warrants action.

Plant early to lessen injury. Use transplants instead of seeds, or plant squash seeds in mid-June.
To prevent egg-laying, wrap a collar of aluminum foil around lower stems or spray the lower plant stems and base of the plant with pyrethrins when adults are flying (mid-late May). Repeat 14 days later. Or sprinkle diatomaceous earth on lower stems.
Cover plants with floating row cover until flowering.
For active borers, make a vertical slit upward from where frass is observed. Use a razor or sharp knife and cut half-way through the stem. Remove and kill borer. Mound soil over the wound to induce supplemental rooting.

Squash vine borer control
Video: HGIC

Bt (Bacillus thuringiensis) or beneficial nematode Stinernema carpocapsae can be injected into wound to kill borers.
Seal up infested vines in plastic bag before larvae pupate (break life cycle.)
Butternut, Tromboncino, and cushaw are resistant; yellow crookneck less susceptible than zucchini.