Squash Vine Borers in the Vegetable Garden

You want the bad news first? Here it is: When it comes to garden pests, the squash vine borer is an absolute beast.

Here's the part where I'd normally give you good news... but I don't really have any. Just a second piece of bad news: Squash vine borers are pretty much inevitable if you're growing squash. Every time I plant squash, I feel like my plants are ticking time bombs just waiting to explode.

And it's not just squash plants—basically every plant in the Cucurbit family can be affected, including zucchini, pumpkins, and gourds, though these pests aren't as partial to cucumbers and melons.

Let's learn a little more about squash vine borers before we talk about ways to minimize their damage in your kitchen garden.

What Are Squash Vine Borers?

The adult squash vine borer is a moth that looks more like a black and orangey-red wasp. I picture these jerk moths just flying around my neighborhood, waiting to be like, "Oh, look, Nicole planted some lovely summer squash and zucchini. Time to wreak havoc again!"

But it's not actually the adults who cause the damage to your plants. It's their ugly little offspring: the larvae. It's these guys that bore into the stems of your plants and leave nothing but destruction in their wake.

Squash Vine Borer Life Cycle

The adult moths lay their eggs at the base of your squash plants. These eggs hatch within a couple of weeks, and then the larvae fatten themselves up by burrowing into the lower stems of your plants and feeding on the soft material inside, at best weakening the plants and at worse killing them. Their feast typically lasts 2 to 4 weeks, and if they get really hungry, they might even go for the fruits on the plant.

These pests then overwinter in your soil inside cocoons and emerge the next summer as adult moths. The whole cycle repeats.

Signs of a Squash Vine Borer Attack

The first sign that these little beasts are present in your garden will likely be wilting leaves on your squash plants. If you've recently watered, it's time to do an inspection of your plants. Check around the base first for holes or "frass". When squash vine borers start gnawing through your stems, they leave behind chewed-up plant material that looks like green or yellowy-orange sawdust.

Plants usually can't withstand this kind of damage for long. The leaves and stems will rot around the damaged area or become super brittle. The plant will stop thriving and potentially die.

If a client calls me and says something like, "My squash plants just all of a sudden aren't doing well," I typically assume it's squash vine borers.

How to Prevent Squash Vine Borer Attacks

In my experience, there's no way to fully prevent the squash vine borer. There are, however, some things you can do to prevent a total wipeout of your squash crop.

Use Garden Mesh or Row Covers

A simple physical barrier is a great way to keep flying pests out of your garden, and if the adults never have access, they can't lay their eggs at the base of your plants. Cover your plants with garden mesh or a floating row cover from the day of planting to keep pests out (this works for cucumber beetles, too).

Once flowers begin to appear, you'll need to remove the covers during the day to give pollinators access to your plants. Unfortunately, squash vine borer moths are also active during the day. The hope is that they won't be looking for a place to lay their eggs by the time your squash plants are maturing.

Wrap the Stems of Your Plants

Another form of physical protection is to wrap the stems of your plants with strips of nylon or foil. This also prevents the moths from laying their eggs. The barrier should go about an inch above and below the soil line to cover the most desirable egg-laying areas.

Keep the Soil Around Your Squash Plants Nice and Clean

To prevent pests and disease, I regularly clean the soil area by removing fallen leaves and debris. I never mulch around my squash plants because bark and straw just give the squash vine borers a nice little place to hide out.

Plant a Large Variety of Different Plants

If you really love squash, then grow a lot of squash plants but spread them out. Don't have an entire raised bed growing squash and nothing else.

It's also a great idea to plant lots of flowers throughout your garden space to attract beneficial insects like parasitic wasps, which can take care of your squash vine borer problem for you. Think of your garden as a little ecosystem; the greater plant variety you have, the more likely the space will be able to take care of itself.

Plant Early

Some gardeners swear by getting their squash seeds sown as soon as possible after their last frost. The hope is that the squash plants will be strong enough by the time squash vine borers are active to fend for themselves. You might even be able to bring in a harvest and then remove the plants before the larvae come out to dine.

Prune Lower Squash Leaves

Regularly prune the lower foliage, and never allow squash leaves or stems to touch the soil. Use stakes and twine if a plant is leaning over. The idea is to give pests as few access points to your plants as possible.

How to Get Rid of Squash Vine Borers

The best way to prevent a major squash vine borer infestation is to stay active in your garden so you can catch issues early. Check the stems, both sides of the leaves, and flowers for squash vine borer eggs (pictured below) regularly. Knock any eggs you find off the plant. (I recommend wearing gloves and long sleeves to protect your skin from the tiny squash bristles.)

If you find a couple of stems with damage, you can cut them at the base and remove the larvae by hand.

If you really want to keep the plant in your garden, you can apply Bacillus thuringiensis (Bt), a natural insecticide. Make sure to follow the directions on the bottle.

Honestly, though, as soon as I see signs of squash vine borers, I harvest as many fruits as possible from the plant and pull it from the garden. Goodbye, squash, see you later! Thanks for the two little squashes! I don't like to keep stressed-out, problematic plants in the garden.

Don't feel bad about removing plants that aren't at their best anymore from your garden. It's necessary sometimes. You didn't do anything wrong. Like I said, these pests just go hand-in-hand with growing certain plants.

When you remove the affected plants, make sure to pull up the roots and throw all plant material in the trash, not in your compost pile.

Now, you have some free space to plant something that's not in the Cucurbit family.

Don't Let Pests Squash Your Good Vibes

Pests are just a natural part of having a garden filled with lots of yummy, organically grown plants. Don't let them get you down. The best thing to do is fill your garden with lots of your favorite plants so that you still have things to harvest even if one plant gets sacrificed to the bugs.

Thanks for being here and making gardening ordinary again (pests and all)!