Wanna Beat Squash Vine Borers? You Need to Start Now

Yes, it’s still only mid-February, but if you want to get ahead of those dreaded squash vine borers this year, you need to start planning now. 

What are squash vine borers

The squash vine borer (Melittia cucurbitae) is day-flying moth with orange-and-black markings that lays eggs at the base of cucurbit plants (squash, pumpkins) in early summer. Larvae bore into stems, causing sudden wilting. If damage is bad enough, it can kill a large plant overnight. 

It’s all about prevention

I don’t like to use the word “organic” to describe my gardening style or the curriculum that I teach. 

This is because the word is grossly misused. There are many products and treatments on the market labeled as “organic” that can still wreak havoc on your garden’s ecosystem. 

For this reason, I teach prevention over treatment, so that you don’t even need to reach for organic pest or disease treatment. No treatment at all is ten times better than any organic treatment for your garden. 

Three best ways to prevent squash vine borer damage

1. Cover plants with floating insect mesh until flowering begins. Insect mesh is a feather-light cover that protects plants from insects while still allowing sunlight and water to pass through. It’s remarkably effective for squash vine borers because it prevents the moths from laying their eggs. Remove cloth once plants begin flowering to allow for pollination.
    
2. Never plant squash in the same place. A very effective way to eliminate problems with pests and diseases in your garden is to rotate where you plant things. When you plant a vegetable, it attracts pest over the course of the growing season. Those pests often stay in the soil long after the plant itself has died and been removed. If you plant squash in the same place that you planted it last year, the pests are laying in wait to attack your plants. Rotate where you plant anything in the cucurbit family.
   
3. Plant squash at the right time. If you plant squash too late in the season (for example, waiting until May to plant squash), you’re giving the squash vine borers a head start. Here in North Texas, direct sow squash seeds in early April once soil temperatures average soil temperature reaches 70 degrees. (Cold soil inhibits germination.) Or better yet, you could even start seeds indoors in mid-March, then transplant seedlings out in early April.

Plant selection matters

Though no squash are impervious to SVB damage, here are five squash varieties known for having better resistance to squash vine borer compared with common zucchinis and summer squash. (Resistance often comes from tougher stems or being in the Cucurbita moschata group.)

Tromboncino (Cucurbita moschata) – A vining heirloom that resists SVB much better than typical summer squash and can be eaten young like zucchini or matured like a winter squash.

Butternut squash (C. moschata) – Winter squash with denser stems that squash vine borers are less attracted to, often making it a reliable choice where borers are common.

Tatume squash – Another C. moschata type noted for SVB tolerance, also productive and useful both as a summer and winter squash.

Zucchino Rampicante – An Italian heirloom climbing squash in the C. moschata family with good resistance and vigorous growth.

Eight Ball squash – a round summer squash that gardeners report as holding up better to vine borer pressure than common zucchini (still not immune, but more tolerant).

Keep in mind that “resistant” doesn’t mean immune; severe SVB pressure can still affect these plants, so integrate the other strategies mentioned above.

What to do when damage occurs

Once squash vine borer larvae penetrate the stem of your squash plant, it’s critical to stop the damage from getting worse. Monitor the stems of your squash plants daily for signs of larvae presence. Not catching SVB early enough is why people lose entire plants. 

Signs of SVB presence

As the SVB larvae consume the stem tissue, they excrete a thick yellow substance. We refer to this as “frass”. This is the first sign of SVB. If left untreated, stems will eventually start to break apart. When this happens, it cuts off water and nutrient supply to your plant. This is why plants suddenly wilt; they aren’t getting any water. 

Treatment strategies

You’ve probably heard of all sorts of things you can do to deal with SVB. Most of them are fairly impractical. I’m a very practical gardener–I don’t believe in wasting time on extreme or complicated measures. 

Here is what I do when SVB strikes: 

1. Spray base of stem daily with Bacillus thurengiensis until larvae die. Bacillus thurengiensis (Bt) is a naturally occurring soil bacterium that produces proteins toxic to specific insect larvae, especially caterpillars, and is used as a targeted biological pesticide that does not harm people, pets, or most beneficial insects when applied correctly. You can spray Bt weekly on stems through growing season as a preventative, but if you follow my prevention strategies this often isn’t necessary.
   
   If you catch damage early enough, this is typically all that you will need to do. Bt works quickly with repeated applications.
   
2. Pick out larvae if visible. If you can see the larvae, you can sometimes pick it out of the stem. Some people say to get a scalpel and surgically remove it, but I would never waste my time doing this. Of course, if this sounds exciting to you, then by all means, don’t let me stop you from experimenting with “squash surgery”. But remember that you do NOT have to do this like some people may have told you. 

Your next steps

Remember how I said that you need to start now to prevent SVB damage? 

Here’s what to do: 

1. Prep for starting seeds indoors in early-to-mid March. Assemble seed-starting supplies, and mark on your calendar or in your planner when to start your seeds. You can master the art of indoor seed-starting with our bestselling indoor seed-starting course and follow-up guidance from me. It’s available to all enrolled students. Learn more about enrollment here. 
   
2. Buy insect mesh. There are many different insect meshes available.  (Pro tip: Pay attention to mesh dimensions. Some are huge. Make sure it’s wide enough to fit over bed and support hoops–if using–without leaving gaps.)
   
3. Buy Bacillus thurengiensis. Remember how I said I’m a practical gardener. When I can save a step, I will, which is why I prefer Bt that is pre-mixed for me. This is the Bt that I have been using recently: https://amzn.to/4rv6VSu.
   
4. Stock up on seeds. My favorite squash are Costata Romanesco and ‘Sophy’. I buy them from Johnny’s Seeds.

Grow more squash

Ready to take your summer vegetable garden to the next level? When you enroll in The Dallas Garden School you get access to every live class and our entire course library which includes “Growing Fruits & Vegetables in North Texas”, your guide to better growing. Enrollment also includes 1-on-1 help directly from me. Yep, expert on call.

Learn more about all the benefits of enrollment, and join our passionate community today.

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