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Good Growing

Dealing with Squash Vine Borer

After years of hiding, I poke my head out, making sure it is all clear. For the past few years, there has been no sign of the intruders. As I gather my courage, I kneel down to plant…summer squash!

My hesitation over the past few years to plant any summer or winter type squash can be summed up in three words- squash vine borer. In 2014, I planted several zucchini plants, a kind of squash, in the garden. I was pleased with their fabulous growth, and it was not long before my family was enjoying tasty stir-fry, zucchini bread, and more zucchini than we could consume.

On a mild summer day returning to the garden to check the harvest, I instead found tragedy. All the zucchini plants had wilted seemingly overnight. My mind went immediately to the only pest with such destructive potential. The squash vine borer.

As an adult, the squash vine borer is a clear-winged moth, sporting a bright red/orange abdomen and a row of black dots on its back. While one may admire these striking colors, the vibrant markings make this adult moth hard to miss.

After mating, the adult female moth will lay her eggs on the squash vine stem near where the plant emerges from the soil. Upon hatching the larvae will burrow into the stem of the plant and begin to feed on the interior, eventually cutting off the flow of water and nutrients from the roots. Evidence of squash vine borer activity is the sawdust-like frass (bug poop) they push out of their entrance hole.

Sure enough at the base of all my plants was the frass deposited by the feeding larvae. There are two options in this situation 1) plant a new crop of squash, or 2) do some plant surgery and remove the feeding larva. My preference being revenge, I grabbed a razor blade, tweezers, and paper clip.

To remove the squash vine borer larvae, cut a vertical slit in the vine near the entrance hole. Gently pull open the vine to expose the grub-like caterpillar and grab it with tweezers or stab it with the paper clip. After removing the caterpillar mound soil over the affected area of the vine as some squash will readily develop adventitious shoots. Of my four zucchini plants that were affected one fully recovered and started producing again, two died, and while the fourth didn't die, it also didn't provide any substantial zucchini.

To prevent infestations in the future make sure to practice crop rotation. Left on their own to consume your plants, the squash vine borer larva will get its fill then exit the vine, and drop into the soil nearby to pupate over the winter. Come next spring the adult moth will emerge from its cocoon in that same spot, so make sure your squash isn't there!

You can protect your crop through physical exclusion with floating row covers, a fabric spun material that lets light, air and water through, but not insects. Squash require the service of pollinators, so once the plants begin to bloom, remove the row covers to grant access to bees and other pollinating insects.

Pheromone traps are available to determine if squash vine borer is active. While not effective at control, squash vine borer traps can indicate when it is time to implement control measures.

Apply insecticide treatments before the larvae bore into the vine. Spray the base of the plant where it emerges from the soil and up the vine about one to three feet. To protect pollinators never spray the flowers and apply in the late evening.

Biocontrols such as Bt (Bacillus thuringiensis) and Entomopathogenic nematodes have shown to be successful when applied with similar timing as conventional insecticides.

Scouting the garden last week I watched a squash vine borer moth fly from squash to squash laying her eggs. I'm hoping to be sick of zucchini by summer's end. Now is the time to begin control measures.