Do you grow squash? Does your plant go crazy and produce so many pumpkins that your family is sick of eating them, and you secretly drop the zucchini on your neighbor’s doorstep just to use them up? If so, this post is not for you.
This post is for gardeners who are having trouble harvesting pumpkins successfully. It’s not because there’s a problem with pollination (here’s a guide to hand-pollinating flowers) or because the flowers keep falling off (this affects squash as much as it does tomatoes). This is because a destructive pest called pumpkin vine borer first invades the crop.
Here’s how to stop it:
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Recognizing pumpkin vine puncture damage
Squash vine borers (not to be confused with squash vine borers, which are a completely different pest) are very prevalent in the southern United States because they have a long spawning period and mild winters, allowing them to produce two generations in a year. (In contrast to northern regions where only a single generation is typically seen.)
However, pumpkin vine borers are found throughout the country, including the Midwest and East, and attack both summer and winter squash crops.
The first sign of pumpkin vine puncture damage is sudden and unexpected wilting of an otherwise healthy pumpkin plant. Pumpkin leaves may go unnoticed at first, as they wilt in the hot midday sun and regrow when temperatures cool.
But if you look closely, you may find unmistakable signs that your plants are inhabited by pumpkin vine borers. A wet, sawdust-like orange substance accumulates near the base of the stem. This material is called frass (a euphemism for insect feces).
You may also find small holes in the stems where pests have entered. The stems may become limp and the roots may begin to split or rot. If the damage is extensive and the stems are already falling apart, the culprit may be visible. It is the larva of the pumpkin flea moth (Melitta cucurbitae), a round, cream-colored, segmented caterpillar with a dark brown head.
They may look small, but they are deadly pests that spend 4 to 6 weeks eating away at the “marrow” of pumpkin vines (they grow up to 1 1/2 inches at maturity) before burrowing into the soil to emerge as adults the following year.
Once you find it, it’s too late to save the plant. But with this simple trick, you can prevent pumpkin vine borers from plaguing your plants next year…
Grow different types of pumpkins
Pumpkin vine borers attack the hollow vines of Cucurbita pepo and Cucurbita maxima. This includes summer squash types (classic zucchini, crookneck squash, patty bread) and winter squash types (pumpkin, delicata, spaghetti, buttercup, and acorn squash).
But do you know what pumpkin vine borers do and cannot eat? Dense, sturdy stems of pumpkins.
If you replace your pumpkin plant with a different variety of pumpkin, you’ll never have to deal with pumpkin vine borers again.
Before you mourn the loss of your favorite zucchini, know that you can eat many different types of winter squash (and gourds, too) as summer squash. Just pick them when they are young and small (i.e. green and immature).
Immature pumpkins are still delicious and 100% edible. It doesn’t have the deep sweetness and richness of fully ripened winter squash. And that’s what makes it taste like summer squash (though it takes a little longer to cook).
A zucchini analogue that also belongs to C. moscata is jehobaku (Korean zucchini). It can be eaten raw or cooked and has a similar mild flavor and soft texture.
Among winter squash varieties, I love Black Ordinary (a Japanese heirloom squash that I also wrote about), Honeynut (a mini butternut type), and Waltham (a standard butternut squash). If these varieties are harvested young, the flesh will be slightly brighter yellow/orange.
If you want to branch out beyond the C. moschata species, you can try other members of the Cucurbitaceae family.
Sechium edule – You may have seen this at the grocery store as chayote squash. Its taste and texture are very similar to zucchini. Lagenaria siceraria – This edible gourd, also known as bottle gourd, cucuzza, or opo squash, is another great substitute for zucchini. Cucuzza usually refers to the long, slender Italian variety, while opo squash is more commonly used in Asian cuisine and has a shorter, wider shape.
I have linked all of the pumpkin vine borer resistant varieties I recommend below.
More ways to outsmart pumpkin vine borers
Growing C. moschata is not the only way to organically control pumpkin vine borers. There are four more things you can do to prevent future damage.
1. Plant later.
Depending on the climate, adult pumpkin vine borers emerge from their underground cocoons during May (warm southern regions) or mid-June to early July (cold northern regions). They begin laying eggs at the base of the host plant, and after a week the larvae tunnel into the stem and begin to cause damage.
Delaying the sowing of summer squash can stop the life cycle of the squash, as the adults mature after they lay their eggs. You can eliminate pumpkin vine borers from your garden by starving them.
If you have a short growing season, choose early varieties and you will have no problems getting a good crop before frost. Personally, in my Zone 5 microclimate (first frost occurs in September), I don’t sow summer squash seeds until mid-to-late June. We always harvest more pumpkins than we can eat.
2. Cover your plants.
If you want to sow pumpkins early in the season, cover your beds with floating row covers to prevent adult pumpkin vine borers from laying eggs on the stems. Be sure to remove the cover once the plant begins to bloom.
3. Catch the larvae.
If you find obvious pumpkin vine borer damage, dig around the base of the plant and look for fat white grubs. To prevent the pests from returning as adults, throw the entire plant, including the larvae, into the trash (not the compost pile).
Leave the soil empty and uncovered for several weeks to give birds a chance to eat the larvae left on the ground.
4. Use beneficial nematodes.
Want to be sure you’ve really removed all the larvae from the soil? Use beneficial nematodes for final control.
I wrote about using beneficial nematodes to control black nematode and combat fungus gnat larvae in the soil.
This type of biological pest control is harmless to humans, pets, and wildlife, but effectively controls targeted pests by introducing millions of predatory nematodes (the good kind) into the soil via watering cans or hose-end sprayers. These nematodes seek out the pupae of pumpkin vine borers and release bacteria that destroy the host. The worms then reproduce and their offspring continue the cycle until there are no more pupae left.
If you want to use beneficial nematodes, look for products that contain Heterorhabditis bacteriophora, an entomopathogenic nematode species that kills vine borers. (Often you can find products that contain a blend of different beneficial nematodes that deal with several types of pests.)
I do not recommend using Bacillus thuringiensis (also known as Bt; who has time to inject this substance into the stems?) or chemical control against pumpkin vine borers. I think getting rid of pumpkins is easy enough with preventive measures and strategic timing of planting. By following the five important methods suggested in this article, you can effectively keep pumpkin vine borers away from your garden.
