9 Tips For Preventing Squash Vine Borers This Season

When it comes to gardening, some pests are worse than others. Many are fairly easy to manage, trap, or even deter altogether. Squash vine borers do NOT fall into this category, and they may easily be one of the top causes of headaches for gardeners each growing season.

SVB’s can attack many different vegetables, but most commonly go after anything in the squash family. While they can be difficult to repel, there are a few tricks of the trade that can help keep them away from your garden this season.

So, if you’re interested in growing zucchini, summer squash, melons, winter squash, or other gourds, this article is for you. Let’s talk about how we can make it harder for this insidious pest to destroy our garden grown squash this season!

What are Squash Vine Borers?

First, let’s identify what squash vine borers are. Mostly found throughout the eastern US (although they are also prevalent in Texas), squash vine borers do just what their name implies. Larvae bore into the stem of a healthy squash plant and destroy it from the inside out.

If you’ve ever tried to grow summer or winter squash, melons, or other gourds, you’ve likely dealt with this pest and learned to hate them very quickly. If you live in parts of the country without them (west coast I’m talking to you!), consider yourself incredibly lucky!

Adults are an orange and black moth that look quite a bit like a wasp. In fact, if you have a lot of wasps in your area, you may have overlooked them in the past.

But don’t be deceived! If you notice the presence of adult moths, you can take quick action to look for eggs before they hatch into very destructive larvae.

Adult moths overwinter in the soil and emerge in early summer (late June to early July) to lay their eggs at the base of squash plants. As moths, they are mostly active in the evening and you can sometimes see them resting on the upper leaves of your plants.

After the tiny eggs hatch, the new larvae burrow into the stem of your plant and begin to eat. As the pests suck sap and chew up the stem, they cut the flow of water to the rest of the plant and it will quickly die.

The SVB has three stages to its lifecycle:

Eggs

The eggs are tiny, flat, oval, and brown. They’re very difficult to see against dirt and mulch, but you may find them in loose groupings (but not tightly clustered) if you get close. Check the undersides of leaves as well.

Larvae

You’ll only ever see the larvae if you slit open the base of an affected stem. If the plant is infested, you’ll see the inch long fat, white body destroying your plant. They’re really quite gross.

Adult Moth

The adult looks a bit like a wasp, but is really a moth. If you see these in your garden at all, take immediate action.

Identifying Squash Vine Borer Damage

Damage from squash borers is very distinctive. Once you see it, you’ll always know what you’re looking at. First, your squash will appear heavily wilted even though the soil is still moist and the plant looked perfectly healthy in previous days.

This wilting occurs because water is no longer moving through the stem and reaching the leaves. But the most distinctive indication of infestation is an orange-yellow “frass” found at the base of the stem. This looks a bit like sticky sawdust and is the remains of the chewed up stem left behind by the vine borer larvae.

Unfortunately, once the visual signs of infestation are apparent, there’s nothing you can do to save the plant. This can be heartbreaking, but take solace in the fact that there are things you can do to protect future crops and even learn how to avoid squash vine borers altogether.

Squash Vine Borer Prevention Tips

Okay, so now that you know all about these annoying pests, it’s time to explore the best way to prevent them from hanging around your squash in the garden this season! Let’s jump into my top tips to keep SVB’s away from your garden grown squash!

Plant Your Squash After Mid-July

In all honesty, the best and most foolproof way of preventing this troublesome pest is to wait and plant your summer and winter squash plants after mid-July. Zucchinis and summer squash are very fast growers, often producing fruit 50 days after seeding.

So even if you have a shorter growing season, I promise there is plenty of time for a bumper crop. Timing may be a little tighter for winter squash in some climates, but if the delay saves the plant and harvest, it’s definitely worth it.

If you are in a warmer climate like Texas, get your first crop planted in mid-March. This will ensure you have time for harvesting before adult moths emerge in May.

By waiting to plant (or planting early in warmer climates), emerging adult moths have nowhere convenient to lay their eggs, and they’ll naturally move on to other areas.

This not only saves your current crop, it may help with prevention in the next year. Since no eggs were laid in your garden bed, no larvae hatched to then overwinter in the soil.

Start Succession Planting

If you don’t want to wait until later in the season for your zucchini or summer squash harvest, succession planting may help. Often vine borers focus on a single plant.

I have seen this in my own garden. I had two cantaloupe planted on the same hilled mound a few weeks apart from one another. One was infested by squash borers and the other was perfectly fine. I simply pulled out the infested plant and enjoyed melons from the other all season.

My recommendation is to plant a new zucchini or summer squash plant every 4 weeks. If one plant falls prey, the next group of plants is ready to step up and produce. This works especially well with quick growing summer squash varieties, but you can also do this with other members of the cucurbit (all the gourds – squash, melons, pumpkins, etc) family.

Practice Crop Rotation in Your Garden

If you’re set on an early season crop of summer or winter squash, there are certainly things you can do to actively protect your plants. The first and easiest is to practice good crop rotation.

This means, you will not plant your squash plants in an area where other cucurbits were planted previously. Just like with fungal disease prevention, this will ensure your plants are in a different area of the garden from the overwintering squash borers.

Ideally, you will plant your new crop fairly far away from the previous years’ to ensure that emerging moths can’t easily find their way to your young plants. If you are planting in containers, it can be helpful to completely replace the dirt if you’ve had previous issues with squash borers.

Start Companion Planting

Companion planting is a great way to keep away SVB’s. The most common companion plants that will keep them away are nasturtiums and mint, as the scents of each plant will tend to keep these troublesome pests away from your garden. Not only that, but both of these plants can keep other unwanted pests away from other garden vegetables.

Another popular vegetable companion, is radishes. They are a rooting vegetable, and won’t compete for the same nutrients that your squash needs. Radishes also have a pungent smell that is known to repel pests, similar to mint and nasturtiums.

‘Shield’ Your Squash With Aluminum Foil

Shielding the stem of your squash plants is one of the more popular online remedies of actively deterring squash vine borers. It’s pretty easy, but can be hit or miss in its effectiveness. Even if you do everything correctly, there is the possibility that other portions of the plant are at risk (like branches that touch the ground) from larvae chewing through.

With that said, if you’re interested in this preventative option, take a piece of aluminum foil (I like the heavy duty stuff for this task) and cut a strip several inches tall. Wrap this carefully around the stem of your plant making sure you dig it at least an inch under the soil line.

This creates a barrier between your plant and squash borer larvae that is very difficult to chew through. Be careful that the foil doesn’t rip and that there are no holes. Otherwise, you will have opened a window for larvae to enter through.

You’ll need to adjust the tightness of the foil as the stem of your plant grows.

Use a Row Cover

Using a row cover can be a sure way to keep squash borers off of your zucchini plants (unless they happen to be overwintering in the soil underneath the cover).

Row covers are lightweight fabric that lets in light, air, and moisture while keeping insects out. The downside of using row covers with squash plants is that it keeps ALL insects out including pollinators.

So, be forewarned, that if you choose to add a row cover to your squash plants, you’re committing to hand-pollinating all the female flowers that open. This is 100% doable, but it’s always a good idea to know what you’re getting into.

Plant Resistant Varieties

If you’re really struggling with squash vine borers in your area, you can focus on planting varieties that are naturally resistant to them. Not only will you avoid the loss of your plants, you’ll get the opportunity to try something new. There are so many interesting types of heirloom squashes to grow and enjoy in your garden this year.

Squash in the Cucurbita moschata family are especially resistant to SVB’s and most pests. Check out butternut squash, yellow crookneck, and zucchini rampicante. Zucchini rampicante – or Tromboncino – is a vigorous Italian heirloom variety that can be eaten early as a summer squash or allowed to grow (HUGE!) as a winter squash.

In the Cucurbita maxima family, hubbard squash varieties like Blue Hubbard, Boston Marrow, and Golden Delicious are reported to be resistant. Cucuzzi – known as the snake gourd – is a delicious heirloom gourd that tastes the same as sweet squash or pumpkin.

And the Green-striped Cushaw is an heirloom grown by indigenous peoples that tolerates drought conditions and is resistant to most pests.

Introduce Parasitic Wasps

In my experience, natural predatory insects are the best defense against pests. Parasitic wasps are a natural predator of a number of pests including squash vine borers. If you are able to introduce them into your garden, they may be able to help keep the vine borer population down.

Parasitic wasps are stingless insects that are one of your best friends in the garden. They’re probably best known for their love of aphids, but they also love to eat the eggs of SVB’s. Keep in mind that a single adult vine borer can lay up to 150 eggs.

So if you have a large infestation, there’s only so much a few parasitic wasps can do. But, if you have a healthy ecosystem that naturally attracts a host of predatory insects, you’ll be one step ahead of the game!

You attract parasitic wasps to your garden the same way you attract other predatory insects and pollinators. Plant herbs and flowers that supply the nectar and pollen they need and the insects will do the rest!

Parasitic wasps, in particular, really love umbrella-shaped flowers and herbs. Try planting Queen Anne’s lace, dill, cilantro, fennel, zinnias, and thyme in close proximity to your squash plants.

You can also purchase parasitic wasps to release directly into your garden. If you do this, ensure you have their desired flowers and herbs nearby otherwise they’ll just fly away!

Conduct Surgery on Your Plant

If all else fails and you notice an obvious entry hole on the stem of your plant with some frass around it, you can try to conduct a little plant surgery. This will only be effective if you catch the problem before your plant starts to wilt. If that has already happened, just pull the affected plant and sow new seeds.

But, if you do catch it in time, all you need is a sharp knife, a pair of tweezers, and a strong stomach. I actually find this process fascinating, but it may not be everyone’s cup of tea.

Make a small incision up the stem (not across it or you will sever the stem) near where the entry hole is located. Squash stems are hollow so you only have to cut enough to break through the outer part of the stem.

Cut only as much as you need to find the larvae. You’re looking for a white grub with a black head – they’re impossible to overlook. Pull out all the larvae you find (there will likely be more than one) and put them in a jar of soapy water. Alternatively, if you have chickens, I hear they love gobbling them up!

Once you have removed all the larvae you can find, gently bury the stem with soil and mulch. Just like tomatoes, your squash plants will be able to close the wound and grow new roots from the buried stem.