Squash vine borer is an insidious little bug that can wipe out your precious squash crop. Here’s how to prevent the heartbreak of ravaged squash plants and what to do if you see signs of damage.
Every year, gardeners like me happily poke seeds into our soil for another season of growing. We water. We watch. We wait.
And sometimes we wish we hadn’t bothered.
Every year I have to choose which crops can fit in my not-so-big garden and which I should simply buy from the farmers’ market or my CSA. I want to make choices that provide the most benefit, meaning yummy food and greatest savings.
So every year I have a dilemma.
With limited sun, limited space, and an ongoing war with one of my least favorite bugs, the dreaded squash vine borer, do I give over precious square footage to squashes?
Or do I admit defeat and stick with the crops that generally do better in my often-neglected garden?
Every year, I give zucchini another shot, hoping I’ll remember to keep on garden tasks enough that I can keep the loathsome vine borers out of my garden.
Inevitably, as someone with too much on her plate and more aspirations in the garden than time to fulfill them, I forget to take precautions that would keep these detestable pests from invading my precious zucchini plants.
I’m writing this to help keep me on track this year and hopefully save you from similar disappointments.
What is Squash Vine Borer and What Does It Do?
Their name kind of gives away their schtick. These insects bore into your squash vine and in the process kill it.
A squash vine borer starts out as a little rust-colored egg at the base of your squash plant laid by a squash vine borer moth.
The adult moth is black and orange and looks a lot like a wasp. They have black dots on their orange abdomens and two pairs of wings, one green and one clear, though the clear ones (in back) might not always be visible.
As squash vine borer eggs hatch, white or cream larvae with brown heads make their home inside the stem of your squash plant. Those large hollow tubes on zucchini plants make it easy for them to travel along their paths of destruction.
Winter squash vines take a little more work for them, so the tender stems of my zucchini plant tend to be their preferred habitat.
And not just their habitat, but their food source. You’ll see damage along the stem where they’ve nibbled. The orange-brownish gunk is called frass, which is the term for squash vine borer poop.
As these nasty creatures munch their way through your plant, they damage its ability to move nutrients and water around. The affected leaves will wilt.
Instead of plump, green, rapidly growing zucchinis, you will see their ends start to yellow and soften until they begin to decay, bypassing your kitchen.
Oh, the heartbreak! No zucchini bread, baked zucchini rounds, or crispy zucchini chips!
If you’ve never had trouble with these rotten pests, you might think I exaggerate. But if you have, I’m sure you know exactly what I’m talking about.
First, your vines look a little droopy. Then one squash begins to shrivel. Then another. Soon the whole plant is a sad, withered mass and your zucchini crop is no more. (Cue tragic music.)
If you know how to deter these dreadful critters, you can save yourself much garden agony. I hope some of these prevention strategies work for you!
If you’re reading this after you’ve already spotted the signs of borer damage, read the section on what to do if you see damage for things you can do to eke out a few zucchini before your plant succumbs.
Related: Natural Mosquito Control for a Less Itchy Summer!
Squash Vine Borer Prevention
To prevent the squash vine borer from destroying your squash crop, my local extension recommends placing yellow buckets filled with water around in late June (earlier if you live somewhere warmer than Minnesota, which most of you do). This simple DIY squash vine borer trap helps drown the adults before they can lay eggs on your plant.
Since squash vine borer moths lay only one set of eggs per year, delaying your planting until after that time can keep them from infesting your prized squash plants. Check with your local extension service about timing. In Minnesota, planting in early July should miss the window for squash vine borer eggs, though it makes it challenging to get all the squash to maturity before our first frost. You likely have a longer growing season and will have more luck with multiple plantings.
You can also cover your vines with floating row covers to keep squash vine borer moths from laying eggs on the plants, as long as it’s not an area where you had plants in the squash family planted the prior year. If squash vine borer was there the previous season, squash vine borer moths may emerge from the soil and lay eggs under your row cover. NOT what you want!
Rotating where you plant your squash crops can help as well.
Don’t forget to remove row covers once flowers begin to appear, or pollinators won’t be able to work their magic. You can also try wrapping the stem with cut row cover material extending below the soil line. I’ve also seen people use pieces of ace bandage or aluminum foil.
Related: Get Rid of Fruit Flies with an Easy Homemade Fruit Fly Trap
What to Do If You See Borer Damage
So the buggers are there attacking your plant already. Don’t throw up your hands yet — fight back! Here’s how.
1. Kill the Larvae
If you see signs that the vine is being attacked, you can try stabbing into the vine with a paperclip in hopes of mortally wounding the borer. I haven’t had much luck with this method, but it’s a good way to vent some of your frustration.
Another method for removing the larvae is a little grosser, but works better, so it’s ultimately more satisfying.
I pull off a few stems with visible damage and pull them apart lengthwise. I will often find one of the fat white squash vine borer larvae sitting there, contentedly murdering my plant.
This method works on the hollow stems of summer squash, but not the denser stems of winter squash vines, unless you’re really lucky and a larva is working its way up to a leaf. Mine seem to stay in the stems.
You can try slicing carefully into the stem of your squash vine with a sharp knife anywhere you can see damage and see if you can find any larvae hiding there. Just don’t sever the stem, and you should be able to remove borers without killing your plant.
You can kill any larvae you find by dropping it in soapy water, or any other means that suit you. Just be sure you kill it. Dropping a larva in the compost will likely mean they will continue to plague your garden.
If you manage to remove a few of the larvae, your plant has a much better shot at survival. The next step will help also.
2. Make a Vine Poultice from Garden Soil
You can buy any infested plants a little more time by covering damaged areas of the vine with soil. Having the wound covered can help your plant muddle through awhile longer and may help you see more squash to harvest time.
Anywhere along the vine you spot damage, cover with soil and water well. Keep replacing the soil if rain washes it away, and keep an eye out for damage further down the vine.
Best to remove any flowers and small squash at this point so the plant can put what energy it has into ripening the bigger squash. Its days are probably numbered, but I have managed to eke out several more zucchini from plants that had borers with this method.
Also be sure when you’re doing garden cleanup to toss any affected plant in the trash rather than the compost.
I hope you’ve evaded the worst of the garden predators the heartbreak they bring this season!
Now that you have a bumper crop of squash, here’s what to do with them all:
Have you had problems with squash vine borer? What’s worked for you?
If you have snarky things to say about other destructive insects you battle in the garden, feel free to use the comment section to vent, just keep it PG, K?
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Photo credits: Jim the Photographer, NY State IPM, Massiv99, krzys16