Do you grow squash? Are your plants going crazy and producing so much pumpkin that your family is sick of eating it, and you’re secretly dropping pumpkins on your neighbors’ doorsteps to use them all up? If so, this post is not for you.
This post is for the gardener struggling to get a good harvest of squash. Not because they have trouble pollinating (here’s a guide to help hand fertilize the flowers) and not because they keep getting flower drop (which affects squash just as much as tomatoes)—but because a destructive pest called the squash vine borer gets to their crop first.
Here’s how you can stop it.
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Identifying squash vine borer damage
Vine borers (not to be confused with squash bugs, an entirely different pest) are especially common in the southern United States because the extended spawning window and mild winters mean they can produce two generations a year. (Unlike northern regions, which usually only see one generation.)
But squash vine borers can be found across the country, including the Midwestern and Eastern United States, and they attack both summer and winter squash crops.
The first sign of vine borer damage is an otherwise healthy pumpkin plant that suddenly and unexpectedly wilts. Sometimes it goes unnoticed at first because pumpkin leaves droop in the hot midday sun before puffing up again as temperatures drop.
But if you take a closer look, you may find the telltale sign that a squash vine borer is making its home on your plant: a liquid, sawdust-like, orange substance clumped near the base of the stem. This substance is called frass – a euphemism for insect excrement.
You may also find small holes in the stem where the pest has burrowed into it. The stem may feel mushy or begin to split or rot at the base. If the damage is extensive and the stem is already broken, the culprit may be visible: a plump, cream-colored, segmented caterpillar with a dark brown head, the larva of the squash moth (Melitta cucurbitae).
It may look small at first, but it’s a devastating pest, eating away at the “pith” of your vines for four to six weeks (and growing up to 1 1/2 inches when mature) before burying itself in the soil to emerge as an adult the following year.
Once you see it, it’s too late to save your plant. But you can prevent vine borers from plaguing next year’s plants with this simple trick…
Grow a different kind of pumpkin
Cucurbita vine borers attack the hollow vines of Cucurbita pepo and Cucurbita maxima. This includes summer types of squash (classic squashes, squashes and pattipans) as well as winter types of squash (squash, delicata, spaghetti, butternut and acorn squash).
But you know what vine-holes don’t know and slope gobble; The dense, compact stems of Cucurbita moschata.
Swap your squash plants for different varieties of Cucurbita moschata and you’ll never battle vine holes again.
Before you mourn the loss of your beloved squash, know that you can eat many types of winter squash (and even pumpkins) as summer squash. You just pick them when they are young and small (ie green and unripe).
Unripe squashes are still tasty and 100 percent edible. they just won’t have the deep sweetness and richness of a fully ripe and ripened winter squash. And that’s exactly what makes them taste like summer squash (with a little longer cooking time).
A similar squash that also belongs to C. moschata is aehobak (Korean squash). It can be eaten raw or cooked and has a similar mild flavor and tender texture.
Of the winter squash varieties, I like them Black Futsu (a Japanese heirloom squash I’ve also written about), Honeynut (a type of mini butternut), and Waltham (the standard for butternut squash). When these varieties are picked young, the flesh is a slightly lighter yellow/orange.
If you want to branch out beyond the C. moschata species, you can try other members of the squash family:
- Sechium edule – You’ve probably seen this in the grocery store as chayote squash, and its flavor and texture are very close to squash.
- Lagenaria siceraria – Also known as calabash, cucuzza or opo squash, this edible bottle gourd is another great stand-in for squash. Cucuzza usually refers to the larger, thinner Italian variety, while opo squash is more commonly used in Asian cuisines and has a shorter, wider shape.
I’ve linked to all the recommended squash varieties that are resistant to the vine borer below.
More ways to overcome vine holes from zucchini
Cultivation of C. moschata is not the only way to biologically control squash vine borers. Here are four more things you can do to prevent future damage:
1. Plant slowly.
Depending on your climate, mature zucchini vines emerge from their underground cocoons in May (in warmer southern regions) or mid-June to early July (in cooler northern regions). They proceed to lay their eggs at the base of their host plants and a week later, the larvae burrow into the stems and begin to do their damage.
You can reverse their life cycle by late sowing summer squashes, which will mature after the adult borers lay their eggs. Their hunger will eliminate vine borers from your garden.
Choose an early variety if you have a shorter growing season and you’ll have no problem getting a good crop before frost. I personally don’t sow summer squash until mid to late June in my zone 5 microclimate (with a first frost in September) and I always end up with more squash than I can eat.
2. Cover your plants.
If you prefer to sow squash earlier in the season, cover the bed with a floating row cover to prevent adult squash vines from laying eggs on the stems. Just be sure to remove the cover once your plants begin to flower.
3. Grab the group.
If you see obvious vine borer damage, dig around the base of the plant and look for the thick white pulp. Throw the whole plant, trash and all, in the trash (not the compost pile) to prevent the pest from returning as an adult.
Leave the soil bare and uncovered for a few weeks to give the birds a chance to feast on any lingering plants on the ground.
4. Use beneficial nematodes.
I want to make sure really pull all the roots out of your soil? Use beneficial nematodes for a final clean.
I have written about the use of beneficial nematodes control of root knot nematodes and fight gnat larvae with fungi on your soil.
This type of biological pest control is harmless to humans, pets and wildlife, but effectively manages targeted pests by introducing millions of predatory nematodes (the good kind) into your soil via a watering can or hose sprayer. These nematodes seek out the nymphs of vine borers and release bacteria that destroy their hosts. The nematodes then reproduce and their offspring continue the cycle until there are no nymphs left.
If you want to try using beneficial nematodes, look for a product that contains Heterorhabditis bacteriophora, a nematode insect pathogen that fights vine borers. (You’ll often find a product with a mix of different beneficial nematodes that treat different types of pests.)
I don’t recommend using Bacillus thuringiensis (aka Bt—because who has time to inject that stuff into their stems?) or chemical controls for squash vine borers. I think it’s pretty easy to get rid of them with some preventative measures and strategic timing of your plantings, and if you follow the five basic methods I suggest in this post, you’ll effectively keep vine borers out of your garden.
