What to Do About Squash Vine Borers

Photo found on Flickr, courtesy of La Grande Farmer’s Market.

Have you ever had a healthy-looking squash plant suddenly wilt and die? If your answer is yes, you know the devastation of the squash vine borer. To check for squash vine borers, look near the base of the plants for frass, which is insect refuse that looks like sawdust.

Look closely at the stem where the wilting starts and you may see brown excrement coming out of the stem. Sometimes the stem is split open lengthwise and you can see one or more inch-long borers.

An open slit leaves the plant vulnerable to rot diseases, which can make the situation even worse. In extreme situations the larvae may even eat the crop itself.

Winter squash, summer squash, gourds, and pumpkins are particularly susceptible to squash vine borer. In my garden, zucchinis get hit hard.

Controlling Squash Vine Borers

Sanitation is an important first step to keeping squash vine borers out of your garden. Remove all plant debris from your squash patch after the season and till the ground. Think about rotating your patch, waiting two or three years before planting squash in the same location.

If you stagger your squash plantings some of your crop may escape the worst of the squash vine borers.

I’ve had success with a de-worming technique. Keep a close watch on your plants, looking for frass. At the first sign of borers slit the stem vertically near the where the damage is and remove the borers with a stick or a knife. Then cover the slit stem with soil to encourage roots to form at the nodes. If it works, as it did for me, your vine will resume normal growth.

Organic gardeners control squash vine borers with nematodes, which are microscopic worms that eat the larvae of various insects. Some spray their patch with water mixed with nematodes before planting. If all goes well the nematodes will eat the larvae before they do any damage. If the larvae do get into the stems you can inject nematodes at three or four inch intervals.

Some gardeners report success with introducing trichogramma wasps (which, like nematodes, are considered beneficial insects) into their gardens.

Insecticides may be effective in controlling squash vine borers if you apply them before the larvae enter the plants. If you see the adult squash vine borer, a colorful orange and black moth, you know the larvae are on their way. You can use pheromone traps and lures to monitor the presence of the moths, so you know when to spray. As with all chemicals, read and follow the directions carefully.

Consider planting butternut squash, which has good resistance to squash vine borer, instead of more vulnerable kinds like hubbard.

Want to Learn More About Squash Vine Borers?

Squash vine borers are such a big problem for a number of crops that universities across the country are doing research on the best ways to control the pests. Learn about their ideas at these sites.

The University of Kentucky has info about Squash Vine Borer and Squash Bug.

Squash Vine Borer should be a big help.

Here’s a useful .pdf over Squash Vine Borer.