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Squash Vine Borer

Melitta curcurbitae


Squash vine borers can wipe out the entire year's harvest of squash, pumpkins, or zucchini.
Squash vine borer.

Squash vine borer.

Wikimedia Commons, CC-by-SA license

Description: The squash vine borer is a moth. Squash vine borer larvae are cream-colored, with brown heads, and grow to nearly an inch long. Adult moths resemble red wasps, with black dots on their abdomens and greenish forewings. Squash vine borer eggs are tiny, brown, and flat.

Life cycle: Squash vine borers overwinter as cocoons in the ground, emerging as adults in late June or early July. Adult moths lay eggs on the stems of host plants, usually just above the soil line. Adults will oviposit eggs through mid-summer. When larvae hatch they immediately penetrate the plant stem, where they feed on plant tissue for up to a month. Final instar larvae move into the soil to pupate and overwinter. In southern areas, two generations of squash vine borers may occur in a season.

Crops damaged: Squash, zucchini, pumpkins. Rarely cucumbers and melons.

Signs and symptoms: Sudden wilting is a sure sign of vine borers. Larvae feeding in the plant stems disrupt the flow of water and nutrients within the vine. Careful examination of the stem just above the soil line may reveal entrance holes, piles of frass, or visibile larvae.

Control measures:

  • Monitor for adult moths using yellow pan traps. Place yellow pans filled with water near vine crops in mid-June, and check them daily for adults vine borers.
  • Use row covers or other barriers over susceptible plants when you begin seeing adult vine borers. Be sure to remove any barriers when plants start flowering to allow pollination by bees.
  • Wrap lower plant stems with foil to prevent adults from laying eggs.
  • Monitor plant stems for holes and frass, signs that a vine borer has entered the vine. If you find a vine borer, use a sharp, clean knife to slit the stem open lengthwise and remove the borer.
  • Mound moist soil around the stem after you've removed any borers to encourage root growth.
  • Remove and destroy any dead vines immediately.
  • Turn or plow garden soil at the season's end, and again in spring before planting, to disturb any overwintering vine borers in the soil.

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