The Squash Vine Borer Can Be Defeated

The squash vine borer (Melittia satyriniformis) is a potentially devastating pest to squash plants and other cucurbit plants. The key to preventing their damage is recognizing them early and taking action.


Identifying the Squash Vine Borer

Even the most observant gardener may not know the squash vine borer is present in their garden. Unfortunately, much damage can occur to plants before they know. Learning what the adult, eggs, and the larvae look like is the beginning of stopping any damage.

Adult Squash Vine Borer

Adult squash vine borers are moths that resemble wasps. The moths are only about 1/2 inch long with orange abdomens with black dots and reddish-orange “hairy” hind legs. The front set of wings of the moth are metallic green. The backset of wings are clear and not easily seen. The wingspan of the adult is approximately 1 to 1 1/2 inches wide.

Squash Vine Borer Eggs

Squash vine borer adults, unlike most moths, fly around during the day, laying flat reddish-brown eggs that are about 1/25 inches long. Most of the eggs are laid on the lower one foot of stems near the soil surface.

Squash Vine Borer Larvae

The larvae of squash vine borers are white or cream-colored with a brown head. They can grow to 1 inch long. Frass (insect debris or excrement) on the vines and stems are a telltale sign that the squash vine borer larvae are eating your plant. Unfortunately, this is usually how a gardener learns of the pest’s existence in their garden.

The Life Cycle of Squash Vine Borers

About one to two inches below the soil surface, the overwintering adult larvae transform into pupae living in cocoons. Here the pupae remain in the cocoons until late spring or early summer. The colorful moths emerge, locate a mate, and female moths begin laying eggs on plant stems.

The time between the laying of eggs and the hatching of the eggs is only a few days. The newly hatched larvae immediately begin boring through the stems of the squash plant where they will feast for 14 to 30 days and then return to the soil. Most climates have one generation per year: some have two generations.

Plants that Squash Vine Borers Attack

The squash vine borers attack summer squash, winter squash, gourds, and pumpkins. Cucumbers and melons are also known to be attacked by the borer, but not as frequently as the other members of the cucurbit family.

Signs of Squash Vine Borer Infestation

Today’s beautiful, healthy squash plant can wilt and appear to be dying tomorrow. Greenish or brown sawdust-like frass on the stems means that there are one or more larvae within the stems of the plant. The squash vine borer larvae eat the spongy matter inside the stems cutting off vital water and nutrients to the plant.

Yellow Trap Pans

The yellow trap pan trick can alert the gardener to the squash vine borer’s presence in the garden. By late June, place a yellow container filled with water near the squash plants. Adult squash vine borers are attracted to the color yellow. If the moths are near, they will fly near and fall into the water.

Early Intervention for Control

The damage a squash vine borer inflicts can potentially be stopped if some simple steps are taken. Knowing the borer’s life cycle is crucial in hunting down and attacking these pests before they become huge problems. Here are some strategies that can be taken.

Remove the Source of Infestation

After harvest, remove and destroy old vines that may contain squash vine borer eggs and larvae. Some of the larvae may have already entered the soil for the winter, so till the soil to expose any cocoons that may be there. The birds will eliminate one source of infestation by having a feast on the exposed larvae.

Remove Squash Vine Borer Eggs

The reddish-brown eggs of the squash vine borer are easy to locate on the plant stems. Simply remove the eggs and destroy them. The eggs hatch in a few days, so quickly destroy them. No eggs mean no larvae!

Delay Planting Squash in Spring

Some gardeners practice planting squash later in the season. The theory is that if the moth emerges finding no food source, it moves on to a new location. The late planting may also deter other pests such as squash bugs that attack squash plants.

Use Pantyhose as a Barrier

The adult squash vine borer (moth) lays its eggs on stems usually within one foot of the soil’s surface. When a plant is very young, a covering over the stems can prevent the moth from laying eggs. A 4 to 6-inch circular cut of pantyhose carefully placed over the young plant or pantyhose fabric wrapped around the stems should deter the moth.

Use Aluminum Foil as a Barrier

Another barrier that may be effective is aluminum foil. Cover each stem up to about 10 inches from the soil surface. The reflection of the sun on the foil confuses the moths causing them to look elsewhere for egg-laying locations.

Use Floating Row Covers as a Barrier

Floating row covers (fleece) can protect plants from being ravaged by squash vine borers. The covers are light, white polyester fabric used to protect young plants from insect attack. Do not use row covers if any cucurbit plant grew in that same area the previous year. Overwintering larvae may be in the soil and be trapped under the cover.

Grow Squash Vine Borer Resistant Varieties

There are some varieties of squash that are more resistant to the borer than others. Green Striped Cushaw and Butternut are the most resistant. Summer Crookneck is not as resistant as these, but more resistant than zucchini. Growing these may save a gardener a lot of time and work.

Natural Repellents

Keeping the squash vine borer moth away from or killing the borer will prevent the eggs from ever being laid. There are several natural repellents that are capable of doing this. Here are a few repellents that can be purchased:

  • Neem Oil
  • Hot Pepper Wax
  • Garlic Barrier

Physical Removal of Squash Vine Borer

Gardeners sometimes are plagued with the squash vine borers even after following the prevention and insecticidal measures, but there is no need to despair. There is another option that may save the plant from an early death. The physical removal of the squash vine borer is a sure way to stop this pest. Here are the steps to remove the borer:

  • Locate the sawdust-like frass.
  • Cut a lengthwise slip in stem near the frass.
  • Remove the borer from the stem.
  • Immediately cover the cut area with soil.

Natural Pesticides

There are times when it is necessary to use pesticides, especially if a plentiful crop is desired. Natural pesticides can be slightly toxic to beneficial insects but is a wiser choice than chemical products. There are two natural products that may aid the gardener in the battle against squash vine borers.

Diatomaceous Earth

Diatomaceous earth can be used as a barrier. Simply sprinkle it around the base and on the plant to prevent the larvae from entering the stem. Diatomaceous earth causes microscopic tears in the insects causing them to dry up and die. Rain washes diatomaceous earth off the plants; therefore, a new application will be needed after each rainfall.

Bacillus thuringiensis (Bt)

Bacillus thuringiensis (Bt), an all-natural bacterium produced by fermentation, is lethal to most leaf-eating caterpillars and also squash vine borer larvae. It paralyzes the digestive tract of the larvae. Within one to two days, they die of starvation. Several companies offer dust and liquid forms of the product. The liquid form is best for squash vine borer control.

Using Bacillus thuringiensis (Bt) at the proper time is crucial to controlling or killing the squash vine borer. After the first flowers appear on the squash plants, it is time to begin the injections before any larvae enter; however, it can still be applied after the larvae enter.

Fill a 3-cc hypodermic needle or glue injector with liquid Bt. Inject the center stem about 1 1/2 inches above the soil line, filling the stem with the Bt. If borers are present, inject the Bt about an inch above it. Use about 1-cc per injection. Repeat the injections in about a week. Clean the needle or the injector with bleach and water.