University of Maryland Extension

Squash Vine Borer - Vegetables

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Dead, wilting squash plants

 squash vine borer larva
Squash vine borer larva damaging a squash plant

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: Dr. 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: Dr. Mike Raupp

squash vine borer adult
Adult squash vine borer clear-winged moth

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

  • Plant early to lessen injury. Use transplants instead of seeds. Or, plant squash seed mid-June.
  • To prevent egg-laying, wrap a collar of aluminum foil around lower stems or dust or spray lower stems with spinosad or pyrethrum.
  • 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

  • Spray lower plants stems and base of plant with pyrethrins when adults are flying (mid-late May). repeat 14 days later.
  • 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 and cushaw are resistant; yellow crookneck less susceptible than zucchini.

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