Squash Vine Borer - Vegetables

 squash vine borer larva
Squash vine borer larva

Back to Common Problems - Vegetables

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Appearance

Eggs:  tiny brown flattened ovals attached singly. 
Larvae:  wrinkly, white to cream color hairless caterpillar up to 1" with dark head.

Squash vine borer larva, video by M. Raupp

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.

Squash vine borer adult - video by M. Raupp

Life cycle/Habits 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. 
Host Plants Summer and winter squash and pumpkin. Very rarely in cucumber, gourd, and melon.
Signs/Symptoms 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. 
Monitoring 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.
Prevention/Control
    1. Plant early to lessen injury. Use transplants instead of seeds. Or, plant squash seed mid-June.
    2. To prevent egg-laying, wrap a collar of aluminum foil around lower stems or dust or spray lower stems with spinosad or pyrethrum.
    3. Cover plants with floating row cover until flowering.
    4. 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 larva control, video by HGIC
  1. B.t. or beneficial nematode Stinernema carpocapsae can be injected into wound to kill borers.
  2. Seal up infested vines in plastic bag before larvae pupate (break life cycle.)
  3. Butternut and cushaw are resistant; yellow crookneck less susceptible than zucchini.
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