When your squash plants are suddenly struggling, it may be the work of a squash vine borer. If caught early, it’s possible to save the plant. Learn how to prevent, control, and get rid of this squash plant pest.
What Are Squash Vine Borers?
It can be so disappointing when your squash is thriving and suddenly starts to wilt. This may be the result of a squash vine borer (SVB), which is a type of moth that lays its eggs at the base of squash plants. When the eggs hatch, the larvae burrow (or “bore”) into the lower stems, weakening or killing the plant outright.
Found throughout the eastern United States, squash vine borers typically attack squash, zucchini, pumpkins, and various types of gourds. They prefer Hubbard squash and are not as fond of butternut squash. Other cucurbits, like cucumbers and melons, are not usually targeted.
The borers overwinter in soil as pupae in cocoons. When the adult moths emerge in early to mid-summer, they lay eggs singly or in small groups at the base of plant stems. The eggs will hatch within 1 to 2 weeks of being laid. The larvae will then bore into stems to feed for about 2 to 4 weeks; sometimes, they may also bore into the fruit. In northern areas of North America, there is usually only one generation per year; in southern areas, there may be 2 generations.
Start early! If caught after the eggs hatch, it may be too late. Controlling the squash vine borer is mainly about prevention.
Eggs: The eggs are tiny, flat, oval, and brown. The eggs are laid around the bases of squash plants.
Larvae: If you slit open a stem lengthwise with a fine, sharp knife, you will see the borer larva, which has a fat, white, wrinkled body and brown head; it can grow to about an inch long.
Moth: The adult squash vine borer is a moth about 1/2 inch long. It has a gray or black body, marked with orange-red on its abdomen, legs, and head. The hind wings are transparent, and the front wings are metallic green.
Identifying Squash Vine Borer Damage
First, the leaves of the plant will likely start to wilt inexplicably.
Look for holes at the base of the plant and green or orange-yellow sawdust-like “frass,” which is the chewed up stem that the larvae produces as it burrows into the plant.
Squash vine borer larvae feed on the material inside the stems of the plants. The stem will start to rot at the site of the feeding first.
Control and Prevention
How to Prevent Squash Vine Borers
As with most pests, prevention is key.
Sometimes, the best solution is to start your squash as early as possible. This way, plants will be strong enough to withstand any mid-summer attacks, and you may even be harvesting before squash vine borers become active. If you plant early, you may need to be prepared to cover your plants in case of late frost.
Do not plant squash in the same area two years in a row. Squash vine borers overwinter in cocoons in the soil. Also, clean up and dispose of ALL plant debris in the fall.
As soon as the squash plants are finished for the season, dispose of them. Till the soil in the fall and spring to get rid of overwintering pupae.
Physical barriers can be an effective means of keeping squash vine borers at bay:
Cover the plants’ stems with a barrier, such as strips of nylon stockings or aluminum foil, to prevent egg laying.
Before flowers appear on the plants, use row covers to keep squash vine borers away. The covers will need to be removed for pollinators, eventually. This will not only give you a head start over pests, but protect your plants from strong heat and frost.
Adding beneficial insects such as parasitic wasps to your garden prior to the vine borer’s egg stage can be helpful, as these wasps are the borers’ natural enemy.
If you give up on zucchini, which is susceptible to vine borers, try growing a squash that’s more resistant. Butternut squash and Cucuzzi (Lagenaria siceraria)—also known as the snake gourd—tend to be resistant to squash vine borer attacks.
Plant extra squash for the pests! This pest is around for only 6 to 8 weeks and can only eat so much (or so we think!), so making sure you have plenty of plants to spare can help you avoid a total loss for the season.
How to Get Rid of Squash Vine Borers
If you’re already seeing signs of squash vine borers, use these methods to get rid of them or at least minimize their damage to your crops.
If you catch them VERY early, you can manually remove the squash vine borer. Locate the entry point of the larvae, then slit the stem lengthwise with a fine, sharp knife to remove the larva by hand. One plant can house several larvae. Carefully remove the larvae without doing more damage to the plant. After removal, cover the slit stem section with moist soil above the point of injury to promote the formation of secondary roots. Also, extra rich soil near the vines helps rerooting.
If you can find the entrance holes and “sawdust,” try inserting a wire and thread it through the stem for some distance to kill the larvae inside.
Sprinkle diatomaceous earth around the stalks when the squash vines are small, or the threat of squash vine borers is high (early to mid-summer). Reapply after rain. Also, build up the soil around the vines. Or, sprinkle black pepper around the plants as a defense.
If possible, catch and destroy the moths at twilight or in the early morning when they are resting on the upper leaves of the plants.
There are insecticides that work, too, but timing is critical; they are only truly effective when applied at the time when eggs are hatching.
The bacteria Bacillus thuringiensis v. kurstaki (“Bt”) is a natural insecticide that can be injected into and applied to the squash stems.
Insecticides containing the ingredients carbaryl (Sevin) or permethrin will work on squash vine borers, too. Always be sure to read labels and warnings carefully before application of any insecticide.