Squash Vine Borers

Squash plants can have huge, healthy leaves and ripening fruit when suddenly everything wilts.

Slow wilting is usually the result of too little or too much water or a symptom of vascular diseases, such as Verticillium wilt and Fusarium wilt. When the leaves of cucurbits droop suddenly and the entire plant collapses, it may be due to a fungal disease called sudden wilt. Or it may be squash vine borers.

If you live east of the Rockies, squash vine borers can kill a plant within a few days unless the borers are found and removed. If you live west of the Rockies, and see a squash vine borer, contact your local County Extension Office immediately.

Squash vine borer (Jim, the Photographer) CC BY 2.0

Squash vine borers frequently attack Hubbard squash, pumpkins, gourds, and zucchini. Butternut, cucumber, and melon plants are usually safe from squash vine borers. So far, anyway. 

Squash vine borer identification

Squash vine borers go through complete metamorphosis from caterpillar to moth. The adult moths look like black and red wasps. They are approximately 1/2” long with transparent hindwings and metallic green front wings. Borer larvae look like fat, wrinkled, white caterpillars with dark heads. Squash vine borer eggs are tiny, flat, brown, and oval.

Squash vine borer lifecycle

Adult borers overwinter underground in pupal cocoons. Adult clearwing moths emerge early to midsummer to lay eggs near the stems of favorite foods. These eggs hatch one or two weeks later, and the larvae burrow into plant crowns, stems, and occasionally fruit to feed for 2 - 4 weeks. One sign of squash vine borers is the appearance of piles of frass that look like wet sawdust.

Squash vine borer control

If you see a borer in a stem, you can cut it out with a sharp knife using a vertical cut or insert a sturdy wire into the burrow to kill the larva.

According to companion planting research, planting radishes near your squash plants mat repel squash vine borers. Interplanting squash and corn may disorient squash vine borers because of the different leaf shapes and stalk heights.

These tips can also help reduce the chances of squash vine borer infestations:

• Plant squash in a different location each year.
• While vines are small, sprinkle the area with diatomaceous earth (reapply after rain).
• Dispose of vines as soon as plants have finished producing fruit.
• Use row covers.
• Place a yellow bowl filled with water where borers are suspected. (Adults are attracted to the color and drown.) Yellow sticky sheets can also be used to trap squash vine borer moths.

I hope you never see squash vine borers in your garden.