Why Do My Squash Plants Have Holes in the Stems?

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Why do my squash plants have holes in the stems? In most cases the holes are entrance points made by squash vine borer larvae, a caterpillar that tunnels inside the vine and cuts off the water it needs. The holes are usually near the base of the plant, and they are often found only after a runner or whole plant has suddenly wilted. This explainer covers what the holes mean, how to tell borer damage from wilt disease, when the insect is active, and what extension sources recommend for checking and removing larvae at home.

Quick answer

• Small holes near the base of a squash vine, with sawdust-like frass nearby, are the most common sign of squash vine borer larvae.
• The first visible symptom is often midday wilting, and the damage is usually noticed too late to save the vine beyond the point of attack.
• Splitting the stem lengthwise is the extension method for confirming larvae. Removing them early, and covering the stem with soil, are the home-garden steps the sources describe.

What the holes usually mean

The squash vine borer (Melittia cucurbitae) is an annual pest of pumpkins and squash. The University of Wisconsin extension publication notes that the insect is often not recognized as a potential pest, yet it can be economically important in some years, and winter squash is highly susceptible to attack. The holes are the sign that a larva has entered the stem. After hatching, the larva burrows into the vine and feeds inside, leaving behind a light brown material that looks like sawdust.

The Kentucky extension fact sheet calls that frass the best evidence of squash vine borer activity. Frass usually appears near the base of the plant, at the entrance holes. If you see it, the insect is almost certainly inside the vine. The Wisconsin source also says that larvae boring into a main stem can kill an entire plant, while larvae in a runner usually kill only that runner. A plant that loses its main stem is in serious trouble, so the difference matters when you decide how to respond.

Holes in squash stems are not always caused by this insect. The safest check is to look for the combination of holes near the base, frass, and a vine that wilts suddenly. A single hole on its own does not prove the presence of borers.

How to tell borer damage from wilt

Wilting is the sign that most gardeners notice first. The Wisconsin extension publication says the first symptom of feeding damage is when plants wilt midday. Because the larvae destroy the tissue that carries water, the plant can droop in the heat of the day and look as if it simply needs more water. The Wisconsin source warns that this wilting can be confused with bacterial wilt or Fusarium wilt.

The way to separate them is to look at the base of the wilting vine. Borer injury usually shows entrance holes, and frass may be present near those holes. Bacterial and Fusarium wilt do not leave that kind of tunnel and sawdust. Checking the stem is more useful than adding water alone. If the base of a wilting vine has no holes and no frass, the cause is probably something else, and the sources do not give a full diagnostic list for that case.

Timing matters too. The Kentucky source says that borer damage is usually noticed only after it has done its damage, often in mid-summer, when a long runner or an entire plant wilts suddenly. By then the infested vines usually die beyond the point of attack. A regular look at the base of the vines in early summer gives you a better chance to catch the problem before the wilt.

When the insect is active

The Wisconsin publication describes the life cycle clearly. Squash vine borers overwinter as pupae in the soil. They emerge as moths in late June and July, when about 900 degree days have accumulated. The moth is a day-flying clearwing that looks more like a wasp than a typical moth, which is one reason it is easy to miss. The adult has a rusty orange body with black bands on the abdomen, and its forewings are greenish-brown.

Female moths lay small brown eggs at the base of plants, and the eggs hatch in seven to ten days. The newly hatched larva goes straight into the stem. It feeds inside for 14 to 30 days, then leaves the plant to pupate in the soil. The Wisconsin source describes one generation per year. The Kentucky source describes one to two generations per year in that state, so the number can vary with where you live.

The Kentucky publication gives a monitoring rule based on accumulated heat. It recommends using about 950 degree days as the point to begin checking plants weekly for frass at entrance holes. In practical terms, that usually falls in mid-June in that region. Gardeners who live in cooler or warmer areas will see the timing shift, so a local extension office can confirm the start of the flight in your county.

Checking and removing larvae at home

The Kentucky publication describes what home gardeners can do with the damage they find. At the first signs of sawdust-like frass on vines, slice the vine lengthwise near where the damage is, and remove the borers. Then cover the stem with earth. The source says home gardeners may have some success with this method. It is not guaranteed, because a larva may already be deeper in the stem than the cut reaches.

Burying a few nodes along each vine can help the plant recover. The Kentucky source says this encourages rooting at those nodes, which lessens the impact if borers girdle the base of the vine. The sources do not say how much this helps in practice, and it does not remove the larvae, so it is best used together with checking and removing borers.

Sanitation also matters. The Kentucky source says that vines should be removed from the garden and composted after harvest is complete, so that remaining borers do not finish their development. Leaving old vines in place gives the pupae in the soil a chance to emerge the next year. Clearing the vines at the end of the season is a simple step with a clear purpose.

Prevention and the limits of home control

The main theme across the sources is timing. The Kentucky publication says the key to squash vine borer management is controlling the borers before they enter the stem. Once a larva is inside the vine, the sources say insecticidal control is ineffective. This article does not give chemical instructions, and the extension publications list products and timing for commercial growers that go beyond home-garden practice. If you are considering a spray, follow the label and your local extension recommendations.

The Wisconsin publication also describes floating row covers as one tool. Covers can be placed during the flight period of adult moths to prevent egg-laying on susceptible plants. The same source warns that blooming plants need bees to pollinate flowers, so covers must be removed during bloom to let bees reach the flowers. That trade-off is important for squash, which depends on pollinators to set fruit.

Varieties differ in how much they are attacked. The Kentucky source says winter squash, particularly ‘Hubbard’, is most susceptible, while ‘Butternut’ is somewhat resistant. If borers have damaged a bed in the past, the Wisconsin source notes that those fields are likely to be damaged again. The sources do not give a rotation schedule, so choosing a more resistant type is the only variety-level step they describe.

For related questions about daytime wilting, see why do squash plants wilt in the afternoon, which covers wilting from heat and water movement. For the other common squash stem pest in many gardens, see why do squash bugs appear.

How we chose

We chose these two sources because both are university extension documents that describe squash vine borer directly, and both name the same key signs: wilting, entrance holes, and frass. We read the full text of each source and used only statements that appear in the fetched pages. The Wisconsin document is an older revision, dated 2005 in its text, and the Kentucky publication is revised in November 2019. We used both for the general life cycle and the signs, and we noted where their recommendations differ, such as the number of generations per year.

We did not use product lists or spray schedules, because the scope of this explainer is the insect and its signs, not chemical control. We also did not treat the extension advice as a guarantee for any single garden. The sources describe typical conditions, and local timing will vary.

What we could not verify

The two sources agree on the main signs of squash vine borer, but they do not settle every question a gardener may have. They also do not give a single answer for every region, every squash type, or every stem problem. The statements below describe the limits of what we could confirm.

What the sources do not say

The sources do not give a complete list of other animals or insects that make holes in squash stems, so this article does not rule them out in general. They do not say how often a home garden needs to check plants beyond the weekly monitoring in the Kentucky publication. They do not promise that slicing and removing a larva will save a vine, and they do not measure how much yield is recovered after a stem is cut and buried.

Frequently asked questions

Are the holes in my squash stems always from squash vine borers?

No. The sources connect the combination of entrance holes, sawdust-like frass and sudden wilting with squash vine borer. A single hole alone does not prove the cause, and other pests or diseases can look similar.

Can I save a squash plant that has borer holes?

The sources say that a stem with larvae can be sliced lengthwise to remove them, and that burying nodes can encourage rooting. Recovery is not guaranteed. If a larva has already girdled the base of the plant, the plant may die.

When do squash vine borer moths usually appear?

The Wisconsin publication says moths emerge in late June and July, when about 900 degree days have accumulated. The Kentucky source places the start of the flight near mid-June in that state. Local timing varies, so check with your county extension office.

Is it safe to eat squash with holes in the stem?

The sources do not give food-safety guidance for squash with borer damage. The sources do not address that question, so check local extension advice before deciding whether the fruit is usable.

Should I remove the vines after the season ends?

The Kentucky publication recommends removing vines from the garden and composting them after harvest is complete, so that remaining borers do not finish development. That step reduces the chance of the pest returning the next year.

Sources

• University of Wisconsin-Extension, “Garden Facts: Squash Vine Borer” (XHT1136), https://richland.extension.wisc.edu/files/2012/07/Squash-Vine-Borer.pdf (opened 2026-10-27).
• University of Kentucky Cooperative Extension, “Squash Vine Borer and Squash Bug” (Entfact-314), https://entomology.mgcafe.uky.edu/files/ef314.pdf (opened 2026-10-27).