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The Dreaded Squash Vine Borer & How to Still Enjoy Zucchini All Season Long

 

First, if you want to see me shudder in disgust, don't miss minute 4:05 in the video tutorial :)

And Friends, perhaps you’ve seen these gorgeous moths frolicking in your garden, though I hope you haven't.

The Squash Vine Borer (Melitta curcurbitae) is a great moth to become familiar with because yes, they're beautiful. Also, they're one of the most devastating insects in your garden.

The gorgeous and devastating adult moth of the Squash Vine Borer.

Squash Vine Borers make their home in the base of your squash plants, devouring their soft marrow before killing their host. They're particularly fond of any Cucurbita pepo plant, which includes all manner of zucchini, summer and pattypan squash in addition to pumpkins, acorn, spaghetti, delicata squash and more. 

Thankfully they are not attracted to cucumbers and melons, but most squash, winter squash, and pumpkins can be dramatically affected. I’ve heard and seen horror stories of home gardens decimated by them my entire life. Here’s how to keep them at bay.

Squash Vine Borer Life cycle

Rumi says, love your enemy.

My mother says, know your enemy.

I say you decide :)

Either way, understanding the lifecycles of insects and diseases in your garden is key to preventing and managing problems organically in your garden.

On our farm in the Finger Lakes, squash vine borer adults emerge from their underground cocoons in early July. Though they fly, they strongly prefer to stay close to home. Individual eggs are laid at the base of their preferred host plants (Cucurbita pepo and C. maxima, more on that later) and one week later, the larvae ‘bore’ into the stems and proceed with an all-you-can-eat attitude, hollowing out your squash stem in four to six weeks before burying themselves in the soil to emerge as an adult the following year. This lifecycle awareness is the foundation of the organic management strategy. But first!

Squash Vine Borer Damage 

If you see wilting leaves on your squash, you likely have squash vine borers. It's subtle at first, only notable in the heat of the day when you might expect plants to wilt, but soon the plants will die. To see if you have dry plants or infected plants, investigate your stem, right at the base where it meets the soil. If you see holes and/or moist greenish/orange frass (the hilariously technical term for insect poop), you’ve got a squash vine borer. Here is a vine just beginning to show signs of the marauding larvae:

Here is a very dramatic example of damage, unchecked:

And here is squash vine borer devouring a squash stem, just before it climbs out and pupates in the soil and overwinters to return next season:

Squash Vine Borer Management

Squash vine borers are challenging to manage, though far from impossible.

Once the larvae enter your squash, the most proactive approach is to pull affected plants and kill the larvae.

As with so many things, prevention is the best cure. 

Here are the four best ways to outsmart the squash vine borer:

1) Catch the adult moth! They're pretty easy to see: They're an inch long, gorgeous and nothing else looks quite like them. You'll often hear their buzzing wings before you turn your head to see them, as well. If you're a Jedi, swap them between your palms. Otherwise, know they are attracted to the color yellow (like the flowers of the host plants...!) and if you fill a yellow beach pail with water, they'll often drown themselves.

Bija, a member of Fruition's Flourish Garden Club, snapped this shot of the adult Squash Vine Borer in action. 

2) Catch the grub! Once you see that dramatic damage at the base of your squash plant, dive in and dig around for the fat white-ish grub who is devouring the marrow. It grows every day, finally pupating at about two inches long. If you don't find it, burn the whole plant. I know it's dramatic. But you really don't want to let them live to plague you more and more. Sigh.

3) Starve them out! How? Grow varieties whose genus species are Curcurbita moschata rather than pepo or maxima. Varieties of moschata have dense stems the borers can’t 'bore' into, while pepo and maxima are succulent and sappy, easy for the larvae to bore into.

The bad news: Classic zucchini, summer squash, patty pans as well as pumpkins, acorn, delicata, spaghetti, and buttercup are not moschata. 

The good news: You've still got options! Butternut, long island cheese (our variety ‘Gouda,’ developed by Michael Mazourek at Cornell, is an awesome refinement of long island cheese-style pumpkins) and tromboncino squash are all moschatas. Our favorite moschata of all time is Honeynut (below), Cornell's super small and super sweet butternut with a built-in ripeness indicator, making it easy to know when to harvest.

More good news: You can eat winter squash as summer squash. (Young tromboncinos especially are excellent green on the grill.) Even if you have a significant population of squash vine borers, after three years of being 'starved' out of your garden they will move on.

Only squash of Cucurbita moschata, like Cornell's Honeynut, have vines dense enough to starve and dissuade the Squash Vine Borer.

4) Plant Late!  Late sowings of summer squash in early July will mature after adult borers have laid their eggs, thwarting their lifecycle.

Organic gardening focuses on comprehensive soil and plant health as well as preventive measures, so we’re addressing root causes and not dependent on band-aids. With these four keys, it’s easy to prevent squash vine borer populations from building over the years as well as reduce them once they’ve become a serious issue.

You'll also find Squash Bugs adorning your plants, often by the hundreds. And then thousands. You'll find more of their story, lifecycle, damage, and management here

Sow Seeds & Sing Songs,

Who knew Latin names would actually make your life more abundant?!

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