9 Ways To Get Rid of Squash Vine Borers For Good

There’s a plant emergency when you’re about to harvest squash and come upon a completely wilted plant. Seemingly overnight, stems become languid and lifeless. You’re likely witnessing the quick destruction caused by the dreaded squash vine borer (SVB). 

Squash vine borer is more prevalent in some regions than others. If your area is under an SVB infestation, there are ways to promote healthy squash vines. While treatment is detailed and time-consuming, there are preventative measures to rid the garden of the pests for flourishing squash.

About SVB

Squash vine borer, Melittia cucurbitae, is a moth. Adults are easily recognizable with a bright orange thorax lined with black dots. They fly during the day and look like wasps, buzzing loudly. 

The pervasive pests are found in North America, east of the Rocky Mountains, and from Canada to South America. They occur along the East Coast to the Southeast and Midwest United States. They’re particularly prevalent in the south and are only sometimes a problem in the Western region.

Curcubits are host plants for the larvae. They’ll infest anything in the Curcubitaceae family, especially squash, pumpkins, and gourds. The species is most active during the vines’ primary growing season in mid-June and July.

The female borer lays eggs along the stems, especially near the base. The obscure eggs and hidden larvae are difficult to see. The surest sign is sudden wilt, as larvae block the stems from water uptake.

When the larvae hatch, they feed on the stem’s interior for four to six weeks. The caterpillars are cream-colored with brown heads and reach nearly an inch long.

At maturity, they leave the plant and burrow into the soil. They’ll overwinter until the following summer when they emerge as moths, and the cycle continues.

Scout Regularly

Early detection is the best way to save the plants and eradicate these pests. Look early and often, starting in early June and continuing throughout the summer.

While difficult to see, look for a singular egg along the stem. Females lay up to 250 singular eggs. While most insects lay eggs in clusters, these appear as single, flat, rounded, reddish-brown dots. 

The eggs resemble those of a squash bug, a different insect that lays a cluster of eggs on stems and undersides of leaves. For SVB, we’re looking for individual eggs, often near the base of the plant. You may also see the opening where the borer has entered the stem. A small hole and yellow “sawdust” or frass (waste) indicate the entry point. The stem may also appear cracked and unhealthy.

If you spot the egg, scrape it from the stem. Scouting isn’t foolproof; the eggs are small, and the process is time-consuming when there are other garden tasks to accomplish. Eggs may also be laid on the soil surface, making it even more difficult to find them. 

Bury the Stem

Covering the lower portion of the stem with soil may help reduce infections. The coverage creates a natural barrier, leaving the adult moth unable to access the main stem.

Like tomatoes, squash vines root where the stem contacts the soil. This method serves a dual purpose of growing more roots for sturdy plants while covering the stems. With more roots, plants may withstand an infestation.

However, the resourceful SVB has a workaround. It may lay the egg elsewhere on the plant, especially near a leaf node. When the larvae hatch, they feed and crawl until reaching the main stem, where they continue the process.

Incise the Vine

The most common and effective way to rid plants of caterpillars is to perform vine “surgery.” The procedure involves a small vertical cut along the stem to physically remove the larvae.

Use small nail scissors or a fine blade to make a lengthwise incision where it looks like the borer may be. Take care not to cut through the vine. Pluck the borer out with tweezers and take it away from the site. If you have chickens, they’ll do the dirty work for you.

Bury the fresh cut when possible to allow new roots to develop from the stem above the damaged section. Otherwise, the stem will form a callous over the wound to heal. 

While physical removal ensures no further damage, it may or may not save the plant. While intricate, it’s the best treatment for an active infestation.

Wrap Stems

If you’re only growing a few plants, it may be feasible to wrap the stems. Inventive gardeners use aluminum foil, burlap, or other materials to protect stems from the moths. Wrapping provides a protective barrier against the insect.

Wrapping stems has disadvantages: It’s impractical if you’re growing a lot of cucurbits or have many other plants to tend to. It’s also time-consuming and uses excess materials.

Inject Organic Bacteria

Bt, or Bacillus thuringiensis, is a bacteria that disrupts the digestion of caterpillars and similar pests. It’s a biological control that stops them from feeding.

If you’ve scouted and discovered a borer hole or damage, inject liquid BT into the localized section with a simple needle. It may work if the borer is still in the vicinity. It may seem crazy to perform “plant injections,” but this bacteria is very effective with this mode of delivery.

While spraying plants with Bt is tempting, the bacteria is only effective when the SVB consume it. For borers who feed on the inside of stems, that means targeting the interior.

Bt is only effective against feeding larvae, not eggs, so topical spraying isn’t viable. Spraying also affects the caterpillars we want in our gardens.

Exclude SVB Favorites

Some cucurbit species are more prone to squash vine borers than others. If you live in an infested area, a preventative measure is to stop growing the most impacted varieties.

SVB often affects summer and winter squashes, including zucchini and pumpkins (Cucurbita pepo). Butternut squash, cucumbers, and melons are less affected.

Delay Planting

If you’re not ready to forego your favorite summer squash or pumpkins, work around the squash vine borer’s lifecycle. Delay planting until late July or August. The insect’s season slows as summer wears on, and egg-laying decreases. There’s still time for a yield of fruits, albeit not as prolific as SVB-free growing areas.

Planting later in the summer also reduces the likelihood of the pest overwintering in the soil. Not providing the host plant during the active season breaks the cycle.

Grow Resistant Varieties

Growing resistant varieties is the best means of prevention, in addition to excluding severely impacted crops.

Cucurbita moschata is a resistant species with thin, tough stems that limit access. Native to Central and South America, it also tolerates heat and humidity with better downy mildew resistance.

While some C. moschata are more SVB-resistant than others, here are a few that deter the pest while serving up big flavor.

C. moschata ‘Seminole’

Seminole pumpkins are ideal selections for southern gardens. Multiple tribes in Florida, including the Seminole, Creek, Miccosukee, Muscogee, and Calusa, cultivated the selection.

The large vines produce six-inch bell fruits with firm, deep orange flesh. The flavor is sweeter than other butternuts, making it a good substitute for pumpkin. Harvest in autumn or pick young and early fruits for summer squash.

The cultivar features excellent mildew resistance and tough stems to defend against moths and caterpillars. Squash vine borers have trouble attacking these plants. Mature pumpkins weigh six to twelve pounds. Leafy stems grow as much as 25 feet long.

C. moschata ‘Tromboncino’

‘Tromboncino,’ also called ‘Zucchino Rampicante,’ is an Italian heirloom winter squash. Squash vine borers don’t usually attack it.

While the long fruits mature in the cool season, they’re equally delicious when harvested young, green, and tender in the summer. They provide a tasty stand-in for summer squash and develop their butternut characteristics in the fall.

Trellis the vigorous vines to watch the long, narrow fruits develop as they hang. The unique squash is a conversation piece and reaches up to three feet long.

C. moschata ‘Waltham Butternut’

‘Waltham’ boasts a classic nutty flavor and tender orange flesh. A favorite since the 1970s, the variety is an All-America Selections winner out of Massachusetts. Eight-foot vines are high-yielding, with four to five fruits per plant.

‘Waltham Butternut’ has a sweet taste, isn’t stringy, and has a long shelf life. Fruits weigh three to six pounds and measure 8 to 12 inches. ‘Waltham’ is a highly popular baking squash. 

C. argyrosperma ‘Green-Striped Cushaw’ 

These striped crook-neck winter squashes are as attractive as they are tasty. White skin has light and dark green mottling. A reliable heirloom, ‘Green-Striped’ has vigorous vines that resist most pests, including squash vine borer. 

The flesh is medium-textured and light in color with a mildly sweet flavor. Fruits are 18 inches long and 10 inches wide at the base. These gourds don’t last as long as others in storage.