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Squash vine borers

Quick facts

  • The squash vine borer is a common clearwing moth whose larvae feed inside the vines and crowns of summer squash, winter squash, and pumpkins. 
  • It is active from mid-June through July.
  • In-home gardens and small farms, entire crops may be lost in a year of high borer populations.
  • Feeding by larvae causes yellowing of leaves and wilting.

How to identify squash vine borers

Adults

  • Adult moths are unique in that they fly during the day and mimic wasps. 
  • Moths are about 1/2 inch long with an orange abdomen with black dots.
  • The first pair of wings are metallic green while the back pair of wings are clear.
  • The back wings are folded when they are at rest, and may not be seen clearly.

Eggs and larvae

  • Eggs are flat, brown, and about 1/25 inch long.
  • The larvae are white or cream-colored with brown heads, growing to almost an inch in length.
A black and orange squash vine borer adult rests on a green plant.
Black and orange squash vine borer moths are swift fliers.
Squash vine borer larvae resemble maggots. There is frass lining the hole where the larvae was eating the base of a pumpkin plant.
Squash vine borer larvae somewhat resemble maggots. Here we can see the frass lining the hole where the larvae was removed from the base of a pumpkin plant.

Biology

  • There is one generation per year.
  • Squash vine borer adults emerge in late June or early July, from cocoons in the ground.
  • After emerging, squash vine borers lay eggs singly at the base of susceptible plants.
  • Eggs hatch in about one week and the resulting larvae bore into stems to feed.
  • Larvae feed through the center of the stems, blocking the flow of water to the rest of the plant.
  • Larvae feed for four to six weeks, then exit the stems and burrow about one to two inches into the soil to pupate.
  • They remain there until the following summer.

Damage caused by squash vine borers

A wilting vine crop
The first symptom of squash vine borer feeding is wilting. Look out for plants that are wilted in the morning. 

The first symptom of a borer attack is wilting of affected plants.  

Wilting may occur only in strong sun at first, but if the problem is left unchecked, the plants eventually collapse and die.  If plants are wilted in the morning, they warrant a closer look.

When you look at a wilting plant closely, you might notice holes near the base of the plant.

  • These holes are filled with moist greenish or orange sawdust-like material called frass.
  • Over time, the base may become mushy or rot away altogether.
  • Several borer larvae may attack a single plant.

Managing squash vine borer in home gardens

Squash vine borers are challenging to prevent or manage. Once the larvae invade the stem, it is difficult to treat squash vine borers.

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Managing squash vine borer on farms

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Authors: Marissa Schuh, IPM Extension educator, Jeffrey Hahn, and Suzanne Burkness, College of Food, Agriculture and Natural Resource Sciences

Reviewed by Bill Hutchinson

Reviewed in 2022

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