The Dreaded Squash Vine Borer

If you have grown squash for very long you have probably run across the dreaded squash vine borer (Melitta curcurbitae).  One day your plants look great and the next day the plants look wilted.  Shortly after they collapse and die.  The base of the plant becomes mushy.  You may even see small holes at the stem base.   Squash vine borers have probably paid your garden a visit.

Squash Vine Borer Photo by Jim Jasinski, Ohio State University Extension, Bugwood.org
Squash Vine Borer Photo by Jim Jasinski, Ohio State University Extension, Bugwood.org

To understand how to control this pest we need to understand a bit about its biology.  In June/July adults emerge from under the soil.  They fly during the daytime and lay a single egg at the base of susceptible plants like squash and pumpkins.  After about a week the egg hatches and the larva bores into the plant stem.  The insect will feed through the center of the stem for several weeks.   Then the larva will exit the stem and burrow back into the soil to pupate until next summer where it emerge as an adult.  There is one generation per year.

Knowing this biology we can use integrated pest management (IPM) to help combat this pest.  Choose plants that the vine borers don’t like.  Gardeners have had success with moschata types of squash like butternut.  Their stems seem to be more resistant to the borer.   Next, especially if you have ever had vine borers, you must rotate your crops.  Don’t plant squash in the same place next year because the pest is in the soil waiting until next summer to emerge.

If you have planted in an area that does not have a history of squash vine borers you can use row covers (simply structurally supported netting) to block the flying adults from laying eggs.  As soon as the squash starts to flower you will need to remove the row covers to give the necessary pollinators access to the flowers.  Some gardeners have had success with trapping.  The adults are attracted to the color yellow.  Some gardeners use yellow bowls with filled with water.  The thought is the yellow bowls will attract the insects and they will drown.  Yellow sticky traps are also available.

Squash Vine Borer Larva Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org .
Squash Vine Borer Larva Photo by Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

Change your squash planting time.  If you can plant very early so that the squash will be mature and fruited before the adults lay eggs, you might outwit the pest.  When the squash plant has finished producing vegetables, remove it from the garden.

What if it is too late and you are already infected with squash borers?  One recommendation is to make a sharp slit in the stem and remove the borer.  Afterwards pile soil around the stem so that the wound is covered with soil.  Insecticides can be used for prevention but once the pest is inside the plant, insecticides aren’t very helpful.

If your crop is a complete failure, your local Farmers Market will probably have some squash and you can try again next year.

Contact your UGA Extension Agent for more information on combating the vine borers.  Also, visit Homegrown Summer and Winter Squash by Florkowska and Westerfield for other tips on growing squash.

Happy Gardening!

Becky Griffin

10 thoughts on “The Dreaded Squash Vine Borer”

  1. I love the idea of posts dedicated to various pests and diseases when they are likely affecting gardeners! Great post to help all of us become better stewards.

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  2. I planted our squash in early April. When the buds were beginning to form, I put diatomaceous earth in the middle of the squash. I also planted straight-necked squash instead of the usual crooked-neck. Perhaps it was the timing of the planting that gave me clean squash plants (no infestation)!

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  3. These are some great tips you gave there. I must admit that growing squash has become a lot more difficult than it used to be, thanks to these resistant and quite pesky bugs. I observe my garden quite closely, and I noticed that the pest control remedies that used to work before, nowadays do nothing. I have serious problems with my squash almost every year, but this year the solution I usually use just didn’t work. So, I’ll try what you suggest, with the high hope that it works.

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  4. I have found that Georgia is warm enough for two vine borer seasons. The first waves attacks in late spring laying eggs that leave the plant in late June/July. And then I have a second wave that hatches in mid August. The eggs are easy enough to spot. They have a rust color and are bout the size of a piece of sand. IMO, the best prevention is a combination of insect spray on the stalks and scrapping and crushing the eggs.

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    • Squash vine borers (Melittia cucurbitae) and squash bugs Anasa tristis) are both terrible pests for squash. The vine borer females usually lay their eggs near the stems of the vine while the squash bug females lay their eggs on the leaves of the plant. Later this week I have a post coming out about squash bug eggs. Thanks for your reply!

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    • Can you share with me your results with Tatume Squash? I am very interested to hear how well it performs in your garden. Thanks for sharing!

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