by Erin Hollis
Description: The day flying adults (may be seen sitting on the leaves of squash early in the morning) are primarily orange and black superficially resembling a wasp. The forewings are covered with metallic olive-brown scales. The hind wings are mostly clear with a brown edge. The abdomen is bright red and ringed with black bands. Adults have a wing spread of about 1 – 1.5 inches.
Their Arrival: In Central Texas expect them late Spring/early Summer (usually mid April in my yard) and again in late August
Life Cycle: Squash vine borer refers to a moth that lays reddish-brown eggs singly on most varieties of squash plants. The adult moths will lay their eggs on the tender stems and shaded parts of the baby squash plants. The eggs will hatch in about a week to 10 days and the larvae begin boring into the stem.
The larvae are white or cream-colored with brown heads, growing to almost an inch in length. The larvae will stay in the stem of the plant for about four to six weeks.
Because they feed on the center/inside of the stems, they cut off water and nutrients to the plant, causing it to wilt. Here are some signs there are larvae in the stems of your squash; the obvious wilting of the leaves and stems. Holes in the plant’s stems, usually at the base, where the larvae burrowed inside. Sawdust-like frass colored anywhere from orange-yellow to green coming out of these holes. Signs or rotting in the stem where they have eaten them from the inside out.
When full-grown the larvae climb from the stems and pupate a few inches deep in the soil overwintering there. They emerge as adults in the spring to mate and lay eggs.
Now What Do I Do:
Preventative measures: Soil can be tilled before planting to reduce the number of larvae that are in the soil. Birds may come eat the pupae but look for them and pick them out as you come across them. As your vining varieties grow, you can pile soil every 2 feet or so on the stems. This will encourage rooting at these places on the stem, so that if the borer gets in the stem the plant may still have a chance to grow.
Row cover can be used to protect new crops of squash you may plant, just remember to remove the row cover when the squash has blooms to allow pollination to occur (or hand pollinate). If you are growing in a section that had SVB the previous year/season make sure to also perform the next measure, check frequently for SVB’s and their eggs. They will be trapped under your cover putting those plants in harm’s way but potentially protecting other plants in your garden.
If you leave the squash uncovered, monitor the stems regularly (at least a couple times a week) for eggs. Look along the stems (top to bottom) of the plant and both sides of the leaves, even on the flower buds for the eggs to see if you can locate the solitary copper-colored egg. Remove the eggs. Sticky tape, such as masking tape, ensures they don’t fall into the soil where they can hatch and return to the stem. Another method of removal would be to scrape them off into a container of soapy water.
If you want to leave your plants covered, and since squash are normally bee-pollinated (and the row cover excludes the bees) you will have to take the place of the bee. Find an open male flower (they have the anthers with pollen on them), and dab it onto the female bloom with the pistil. One male bloom will pollinate five to eight female blooms. A cotton swab or small paint brush may also be used, and should occur before 10 a.m. for maximum success. Each flower is open for only one day, so daily pollination is recommended.
If you have squash vine borers in your squash:
Vigilantly keeping watch for tiny holes with brown “sawdust” around them. As soon as you see one, shine a flashlight under the stem (in the evening) to illuminate the borer on the inside. Once you’ve located it, you can stick a pin, needle or small knife through it to stop it’s destruction.
For limited damage, you can remove the leaf stalk if it’s not on a main stem.
Another way to stop a larvae is to remove it from the stem. Slit the stem lengthwise with a sharp knife, I like the thin blade of exacto type craft knife, I cut the larvae and let the stem heal, without removing it. Or you can remove the larvae and then cover the cut stem with a pile of soil on the cut portion of the stem to encourage new roots to grow.
If infested, vines should be removed and destroyed (not composted unless you are sure your compost pile temperature reaches high enough to kill insects) soon after squash harvest. Added measure would be to split stems and joints open to remove and destroy any larvae.
Other Methods of Control:
Yellow Sticky Traps: They’re attracted to yellow. (Word of caution here. I’ve found all things stuck to these. From bees to good spiders and lizards).
Catch Them: The best time to catch adults is around dusk and dawn. If you head out to your squash plants around this time, you may notice adults buzzing around and be able to catch them. (I haven’t been about to get close enough to them to catch one. They move pretty fast, when needed!)
Timeliness: Planning ahead, you could have more seedings started so you can replace the destroyed plant. Master Gardeners often recommend planting squash every two weeks in order to protect your crop. Placing new seeds in the ground may work as well. Just keep them watered as the days get hotter. At some point the SVB’s will disappear until their next “window of opportunity”. Usually mid to late August for Central Texas. Although, I did read in at least one article that they stick around all summer and into November and December. I haven’t had this experience. This was an article for a South Texas audience. Planting really early (March) and then again really late (August) to get harvests while they’re not as active.
Nylon Stocking: Wrapping the stems with strips of nylon stockings, to prevent the larvae from getting in them. (Maybe wrap gauze around the stems.)
Flexible Wire: Insert a thin flexible wire. Instead of cutting into your plant, if you notice a burrow hole, an alternative method is to take a thin, sharp wire and slide it into the hole in the hopes of, essentially, skewering the larvae.
Remove Infestation Early: Getting rid of finished vines and tilling the soil in the fall and spring to get rid of overwintering pupae because these can hatch and damage next year’s crop. At the end of the season. Pull up and destroy all leftover plant vines quickly. You may think that SVBs are done after your squash are harvested and the plants seem to be dead or dying, but this is a mistake. Quite often, larvae will continue to develop inside the vines until they’re ready to climb out and burrow into the soil—unless you dig up the vines and get rid of them. You should also do this with any plants that have been killed by borers during the season as well.
Rotation: Planting squash in a different location each year, so that if some pupae do overwinter in the soil, they won’t find the new plants. (Not realistic, in my opinion, since in most home gardens the size is fairly small and the SVB can fly!)
Plant Extra Squash: Some for you and some for the bores. There are only so many eggs they can lay and they shouldn’t be able to damage all of your plants. I’ll continue to sprout some squash so if you want another plant in a few weeks or later this summer just check in!
Squash Resistant to SVB:
Acorn squash, known as a winter squash because it stores well into the winter, has solid stems and is not usually affected by squash vine borers.
Squash in the Cucurbita moschata family are especially resistant. These include Butternuts, Tatume, and my personal favorite Tromboncinos, a vigorous Italian heirloom that can be eaten early as a summer squash or allowed to grow huge to be stored as a winter squash. If you grow Tromboncinos, be sure you have a lot of gardening space and, ideally, a fence or large, sturdy trellis they can climb on.
Trial in progress: I am trying tulle (bought on amazon - comes in many colors and widths/lengths). Worked great over winter against cabbage moths, etc. Now working great against the SVB and grasshoppers!