Age-Old Wisdom meets Modern Tools
How to Identify and Get Rid of Squash Vine Borers
Are your squash plants suddenly struggling? It could be the work of a squash vine borer. Here are tips on how to identify, control, and get rid of the squash vine borer!
What are Squash Vine Borers?
It can be so disappointing when your squash is thriving and suddenly starts to wilt. The culprit is probably the squash vine borer. The plants wilt because larvae is boring (burrowing) into the lower part of the stems.
Found throughout the eastern United States, squash vine borers attack squash, zucchini, pumpkins, and gourds. They prefer Hubbard squash and are not as fond of butternut squash. Other cucurbits, like cucumbers and melons, are not usually affected.
The borers overwinter in soil as pupae in cocoons. When the adult clearwing 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 one generation per year; in southern areas, there may be 2 generations.
If caught early, it’s possible to save the plant. If caught after the eggs hatch, it may be too late. Controlling the squash vine borer is mainly about prevention.
How to Identify Squash Vine Borers
- Eggs: The eggs are tiny, flat, oval, and brown. The eggs are laid scattered around the bases of squash and pumpkin 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 is a moth about ½ inch long that looks a bit like a wasp with a black body, marked with orange-red. The hind wings are transparent and the front wings are metallic green.
If you see the adult squash vine borer moth, beware that it is probably laying eggs! Photo Credit: University of Wisconsin-Extension.
Identifying Squash Vine Borer Damage
- First, the leaves of the plant will probably start to wilt.
- Look for holes at the base of the plant and green to orange-yellow sawdust-like “frass” (droppings).
- Squash vine borers feed on the material inside the stems of the plants. The stem will start to rot at the site of the feeding first.
Squash vine borer larvae can cause major damage to the inside of your squash plant stem. Photo Credit: Donn Cooper, University of Georgia.
Control and Prevention
How to Get Rid of Squash Vine Borers
- If you catch them VERY early, you can manually remove the squash vine borer. Slit the lower stem lengthwise with a fine, sharp knife to remove the larva by hand. One plant can house several larvae. After removal, cover the slit stem section with moist soil above the point of injury to promote formation of secondary roots. Also, extra rich soil near the vines helps rerooting.
- Or, if you spot entrance holes and “sawdust,” try inserting a wire and thread through the stem for some distance to kill the inside larvae.
- Sprinkle diatomaceous earth around the stalks when the squash vines are small. 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 early morning when they are resting on the upper side of leaf bases.
- There are insecticides, too, but timing is critical; they are only truly effective when applied at the time that eggs are hatching.
- The bacteria Bacillus thuringiensis v. kustaki (Bt) is a natural insecticide that can be injected into and applied to the squash stems, however, it is not usually effective because the larvae are protected inside the plant.
- Many find carbaryl (Sevin) to work, too.
- Consult your local cooperative extension service for advice on appropriate chemical controls.
- Trap the adult orange moths with yellow sticky traps and yellow-colored bowls of soapy water.
- A trap crop of very early-planted Hubbard squash can be used to alleviate pest pressure on other squash.
- Plant extra squash for the pests! They are around for 6 to 8 weeks and can only eat so much (or, so we think!).
- An old folk remedy from The 1963 Old Farmer’s Almanac says that wood ashes were effective against the squash vine borer.
Larvae of the squash vine borer can destroy cucurbit stems if not controlled and prevented. Photo Credit: Lee Jenkins, University of Missouri Extension.
Prevent Squash Vine Borers
- Sometimes the best solution is to start your squash as early as possible. This way you’ll be harvesting before the summer time when vine borers become active. If you plant early, you may need to be prepared to cover your plants in case of frost.
- Do not plant squash in the same bed two years in a row. Squash vine borers overwinter in cocoons in the soil. Also, clean up ALL debris and clean up your soil in the fall.
- As soon as the squash is harvested, get rid of the vines. Till the soil in the fall and spring to get rid of overwintering pupae.
- Preventative measures include covering the stems with a barrier, such as strips of nylon stockings or aluminum foil, to prevent egg laying.
- Adding parasitic wasps to your garden prior to the egg stage can be helpful as these wasps are the borers’ natural enemy.
- One of the better solutions is to cover crops with floating row covers to prevent egg laying (but only if you are sure there aren’t pupae overwintering in the soil). You can also drape these row covers over frames. This will not only give you a head start over pests but protect your plants from strong heat and frost.
- If you give up on zucchini, which is susceptive to vine borers, try growing a squash that’s more resistant such as Cucuzzi (Lagenaria siceraria), also known variously as the snake gourd; it’s pale green and twists and spirals like a snake.
Learn about another main squash and zucchini predator: the squash bug.
Do you have any tips for controlling these pests? Let us know in the comments below!