|Organic Solutions for Squash Vine Borers
A Factsheet from Toxic Free NC
About | Identification | Life Cycle | Prevention | Getting Rid of Squash Vine Borers | Sources
About Squash Vine Borers
The squash vine borer can be a pest of all plants of the cucurbit family, which includes squashes, cucumbers, melons, and gourds, but its favorite is squash. The adult of this pest is a moth, but the all the damage is done by the caterpillar, which tunnels into the stem of the plant and eats the tissues inside. The first sign of damage is usually a small hole in the stem of the plant near the ground, along with a pile of wet, greenish-brown, sawdust-like frass (caterpillar poop - see picture C). The plants may remain healthy looking for a short time, but will soon begin to wilt and ultimately die as the soft tissues of the stem are eaten, cutting off the plant’s water and nutrients.
The squash vine borer can be a disaster for squash plants in the small garden, often resulting heavy or even total losses! By knowing the pest’s life cycle and habits, you can make a plan to avoid the worst.
Sustainable pest management strategies usually work best when used together. Think about your garden, your resources, and your time, and put several of these tips together into a plan that works for you. [top]
Identifying Squash Vine Borers
The adult squash vine borer moth looks a bit like a wasp, 1–1.5” in length, with clear narrow wings. (Here's a picture of a squash vine borer moth.) The body is dark gray to olive-brown, with bright red-orange on the back. Unlike most moths, they fly in the daytime so you may see them in the garden. (See picture A.)
The caterpillars are creamy white and segmented with brown heads (see picture B). Because they spend most of their time inside a plant’s stem, you won’t often see one. The small brown eggs are laid one by one and are hard to spot. (Here's a picture of squash vine borer eggs.) When they’ve been munching on plants, the caterpillars typically leave behind a pile of wet, greenish-brown, sawdust-like frass (see picture C). [top]
Adult squash vine borer moths come out from the soil in late April or early May after spending the winter as pupae (here's a picture of squash vine borer cocoons). They lay their eggs one at a time on the stems of squash plants, usually at the base of the stem near the ground. The eggs hatch in 7 - 10 days, and the young caterpillars dig into the stem to eat, and may stay in there for several weeks. When they’re finished, the caterpillars drop from the plant and dig back into the soil to pupate. Adults continue to lay eggs through August, and in North Carolina there are usually two generations per year. [top]
1) Grow healthy organic plants. Strong, healthy squash plants can handle some damage from squash vine borer better than weak plants. Even if attacked by pests, strong plants will have more time to grow some good squash before they get taken down. Make sure that your plants are in a sunny location in a loose, well-drained soil rich with nutrients and organic matter, and keep them well watered. [top]
2) Grow resistant varieties. Yellow summer squash and zucchini seem to be the favorites for squash vine borers. Butternut squashes appear to their least favorites, and may fare better in North Carolina gardens.
Consult seed catalogs to find information on the species of each squash variety you’d like to grow – the C. pepo types are squash vine borer favorites (yellow crookneck and summer squashes, zucchinis, acorn squashes, etc), and the C. moschata types are their least favorites (butternut squash and some types of pumpkins). C. mixta and C. maxima types fall somewhere in between.
Another general rule of thumb is that the wide hollow stems of cucurbits like yellow squash and zucchini are a great place for a caterpillar to hide and feed. The narrower or more solid stems of cucumbers, melons, and butternut squash are less welcoming. [top]
3) Encourage secondary rooting. Heap moist garden soil or compost along the stems of your plants at several points along the vine. Choose “nodes” where new leaves and growing tips are sprouting from the stem. This will encourage the plant to send roots into the ground at these points, so it can continue getting water and nutrients even if it’s attacked by squash vine borers. [top]
4) Succession planting or strategic timing. If you have a long enough growing season and use some of the other tips (see # 5) for controlling squash vine borers, you may find that succession planting helps. Have new transplants ready to go into the ground when a previous planting gets old or falls to pests.
You can also try to beat the squash vine borer by “pushing” the season. If the weather is mild, you may be able to get a very early crop before squash vine borers all come out, or a very late crop after they’ve finished laying eggs for the year.
5) Keep squash vine borers off your crop. Keep out squash vine borers by covering your seedlings with a light weight “floating” row cover such as Reemay. These materials (as opposed to plastic or heavier fabrics) allow for the free movement of water and air and do not block very much sunlight. They can be found at garden supply stores or ordered from seed catalogs.
The covers can lie directly on the plants (the plants will lift the cover as they grow), or you can support the covers with wire hoops. The trick is to keep the edges of the covers tightly buried or weighted down so that the borer moths cannot get in to lay their eggs. When female flowers appear on your plants you will need to uncover them for pollination by other flying insects.
Covering works very well used together with succession planting (see #4). When it is time to remove the covers on your first round of squash, have another round ready to plant under cover. By the time your first planting gets old or beaten down by squash vine borers, your next succession will be ready to uncover. Or, if you have the patience, you can choose to keep the plants covered all season long and lift the covers daily to pollinate the female flowers by hand. [top]
6) Practice good garden sanitation and till in the fall. Plants that have been killed by squash vine borers or are past the point of saving should be removed from the garden along with their resident pests. Seal them together into a trash bag and leave them in the sun for a few days to bake. That way the caterpillars do not have a chance to move into your soil to pupate. Lightly tilling your garden soil in the fall can reduce the number of squash vine borers the next year by exposing pupae to predators and freezing temperatures. [top]
Getting Rid of Squash Vine Borers Without Toxic Chemicals
7) Cut them out. Keep a close eye on your plants, checking the stems near the ground. If you see the eggs of the vine borer, remove and crush them. It is more likely, however, that you will find the telltale holes in the stem and a pile of caterpillar poop left behind. Squash vine borer caterpillars are protected from predators and sprays once they’ve tunneled into a plant, so one of the only things you can do is “surgically” cut them out.
Starting at the vine borer’s entry hole, use a knife to make a slit along the stem of the squash plant until you find the caterpillar. Be careful not to cut across the stem, as that would cut off water and nutrients to the plant. [illustration] Remove and kill the caterpillar. Look closely, as there could be more than one hiding in there! Cover the cut area of the stem right away with soil or compost to encourage rooting. This is a great strategy for small gardens. [top]
8) Organically acceptable insecticides. As a last resort, you might choose to apply insecticides that appear on the Organic Materials Review Institute’s list of products approved for certified organic farms. However, because squash vine borers live outside the plant for such a short time, it is very hard to control them with insecticides. Once they tunnel into the plant, they are protected from all sprays!
OMRI approved products for squash vine borers include BTK (Bacillus thuringiensis var. kurstaki), pyrethrin, or rotenone. Even though these products are relatively low-toxicity, they can be hazardous. Be sure to follow instructions on the labels very carefully. Keep in mind, too, that these products can also kill the beneficial insects that help your garden. Use as little as possible, and spray only in the early morning or late evening when the “good bugs” are less active.
Spraying for squash vine borers is only effective before caterpillars have entered the vines, so careful scouting is very important. Begin checking your vines for signs of caterpillar poop around mid-May, and at the first sign of damage, you may choose to spray the stems near the base of the plants to control hatching caterpillars. Because adults continue to lay eggs over the entire growing season, it may be necessary to repeat spraying. Obviously, even “organic” sprays come with risks and problems, so try the other tips here first, and you may be able to skip the sprays altogether. [top]
||This factsheet was written with the needs of non-commercial home, school and community gardeners in mind. Certified Organic growers, or those seeking a certification, should check with their certifying agency before using ANY insecticide. Some organically acceptable insecticides are approved for use in Certified Organic systems only against certain pests or in certain situations.
Ellis, Barbara and Bradley, Fern Marshall, editors. The Organic Gardener's Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy Without Chemicals. Rodale Press, 1996.
Adam, Katherine. “Squash Bug and Squash Vine Borer: Organic Controls.” National Center for Appropriate Technology: ATTRA – National Sustainable Agriculture Information Service. 2006. Viewed March, 2012: [link]
Teasley, Donna. “Garden Alert - Squash Vine Borer.” NC State University Cooperative Extension Service, Burke County Center. 2008. Viewed March, 2012: [link]
Bessin, Ric. “Squash Vine Borer and Squash Bug.” University of Kentucky College of Agriculture, Department of Entomology, Cooperative Extension. Revised 2009. Viewed March, 2012: [link]
Jackson, M, Canhilal, R, and Carner, G. “Trap monitoring squash vine borers in curcurbits.” Journal of Agricultural and Urban Entomology. 22(1): 27-39 (January 2005). Viewed March, 2012: [link]