Good Growing: Managing squash vine borer in the garden
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Squash vine borer caterpillars will feed inside of squash vines, often causing them to wilt and potentially die. Photo by Ken Johnson, University of Illinois Extension.
There are a variety of insects that will feed on squash. One of the more troublesome is the squash vine borer. If you’ve grown squash and had a runner or two start wilting, there’s a good chance you’ve had an encounter with squash vine borer.
Squash vine borers will feed on both summer and winter squash and pumpkins as caterpillars. The adult moths are 5/8 of an inch to one-inch long and colorful. Their abdomens are usually orange with black dots. Their front wings are greenish-black, while the hind wings are colorless with dark veins.
The adults fly during the day, often darting around in a zig-zag pattern. They will emerge from mid-June to early July and lay eggs, primarily near the base of stems, but they can be found on other parts of the plant.
The caterpillars will bore into the stems and begin to feed. When they enter the plant, they will leave a small hole, and as they feed, they will push sawdust-like frass (insect excrement/poop) out of the hole, accumulating over time. While the larvae are most commonly found near the base of the plant, they can be found throughout the plant.
As the caterpillars feed, they will tunnel through the stems. This will often cause wilting of vines, especially during the heat of the day. As feeding continues, the vines the caterpillars are feeding on may eventually die. The larvae will grow to be about one inch long, with a whitish body and brown head. After feeding for four to six weeks, they will emerge, burrow into and eventually pupate.
Often, by the time gardeners notice their damage, little if anything can be done. Fortunately, there are steps you can take to prevent them from attacking your plants and, if caught early enough, steps you can take to control them:
Covering plants with floating row covers can help keep squash vine borers off plants. If you have had trouble in the past, make sure you are growing in a different area since they overwinter in the soil. Covers will need to be removed, or plants will need to be hand-pollinated once plants begin producing female flowers.
Some cucurbits are more susceptible to squash vine borer than others. Summer squash, zucchini, acorn squash and Hubbard squash are some of the most susceptible.
Scout your plants for the presence of larvae. If you notice any frass, you can cut the vine lengthwise near the entry hole and remove the larva. Once the larva is removed, cover the stem with soil.
If you decide to apply pesticides, apply them to the plant’s crowns and runners when they begin to run. Once caterpillars are inside of the plants, foliar pesticide applications won’t have any effect on them.
Good Growing Tip of the Week: Good sanitation can help reduce squash vine borer populations. When you are done with your squash and pumpkins in the fall, remove the plants and shred or otherwise destroy them. This will help get rid of any larvae that may still be present in the vines.
