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Watch Out For Squash Vine Borers

While growing your own vegetables can be quite rewarding, it can also be frustrating, especially when a lush squash plant seems to up and die in a matter of a few days. If you’ve ever attempted to grow squash and had plants that suddenly collapsed, it may have been the work of squash vine borers.

Newly emerged adult squash vine borer is a rather attractive, day-flying moth that looks more like a wasp than a moth.

Newly emerged adult squash vine borer is a rather attractive, day-flying moth that looks more like a wasp than a moth. Paul Thompson, ©2019, Clemson Extension

The squash vine borer is a rather attractive, day-flying moth that looks more like a wasp than a moth. The female lays tiny, copper-colored eggs on the stems of plants. As the eggs hatch, the larvae, which look like little white grubs with dark heads, burrow into the stems to feed. It’s all downhill from here since water can no longer flow past the damaged stem.

It’s extremely difficult to control these troublesome insects once they get in the stem, so prevention is key. Row covers can be used but will either need to be removed when flowers appear, or plants will require hand pollination. Regular monitoring can also be effective but spotting those tiny eggs requires a keen eye. Once seen, eggs should be removed and destroyed immediately as they can hatch in about a week’s time.

If you observe sudden wilting, inspect the stems of the plant for yellowish, sawdust-like material which indicates a borer at work. If a borer makes it into a stem, it’s time to engage in warfare. At this point, you don’t have much to lose so you might as well try to save the plant. Use a small knife to make a vertical (lengthwise) slice into the vine in order to remove and kill the larva. Place soil over the slit stem to encourage root development and keep the plant thoroughly watered.

After observing the yellow, sawdust-like material, the affected stem was cut away revealing the squash vine borer larva inside.

After observing the yellow, sawdust-like material, the affected stem was cut away revealing the squash vine borer larva inside.
Terasa M Lott, ©2019, Clemson Extension

Squash borer larva removed from stem.

Squash borer larva removed from stem.
Terasa M Lott, ©2019, Clemson Extension

Encountering squash vine borers is pretty much a given. Plant early and more plants than you need. If you happen to be spared, you’ll have plenty to share. If not, hopefully you’ll still have enough to make a few casseroles.

For more information on growing squash as well as insect and disease control, please see HGIC 1321 Summer Squash, HGIC 2207 Cucumber, Squash, Melon & Other Cucurbit Insect Pests, and HGIC 2206, Cucumber, Squash, Melon, & Other Cucurbit Diseases.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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