Squash Vine Borer

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Here are tips on how to identify, eliminate, and control the squash vine borer.

What are Squash Vine Borers?

Squash vine borers are very difficult to control.  If your plants suddenly wilt because larvae may be boring within the lower part of the stems our at the stem nodes. Look for holes and sawdust-like frass (droppings).

They attack squash, zucchini, pumpkins, and gourds. They prefer Hubbard squash and are not as fond of butternut squash. Cucumbers and melons are not usually an issue.

The borers overwinter in soil and lay eggs within the stem. If caught early, it's possible to save the plant. If caught after the eggs catch, it may be too late. Controlling the squash vine borer is mainly about prevention.

How to Identify Squash Vine Borers

The eggs are small, flat, oval, and reddish. If you slit open a stem lengthwise with a fine, sharp knife, you will see the borer and eggs. The larva is a caterpillar with a fat, white, wrinkled body and brown head.

The adult is a moth that looks a bit like a wasp with a black body body, marked with orangish-red. The hind wings are transparent and the front wings are metallic green.

How to Control Squash Vine Borers

  • Slit the lower stem lengthwise with a fine, sharp knife to remove the caterpillar and the egg masses by hand.
  • Or, if you spot entrace holes and "sawdust," try inserting a wire and thread through the stem for some distance to kill the inside larvae.
  • Then cover the slit stem section with moist soil about the point of injury to promote formation of secondary roots.
  • Also, extra rich soil near the vines helps rerooting.
  • If possible, catch and destroy the moths at twilight or in early morning when they are resting on the upper side of leaf bases.
  • There are insecticides, too, but timing is critical; they are effective when applied at the time that eggs are hatching. The biological insecticide B.t. (Dipel) is not usually effective. Many find carbaryl (Sevin) to work. See your local garden store for advice on appropriate chemical controls.
  • Preventative measures include covering the stems with a barrier, such as strips of nylon stockings, to prevent egg laying. 
  • Cover lower stems with floating row covers (or even aluminum) to prevent egg laying.
  • Importing parasitic wasps prior to the egg stage can be helpful as these wasps are the borers' natural enemy.
  • A trap crop of very early-planted Hubbard squash can be used to alleviate pest pressure on other squash.
  • As soon as the squash is harvested, get rid of the vines. Till the soil in the fall and spring to get rid of overwintering issues.

See our Squash & Zucchini page for more plant care tips.



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