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Squash Vine Borer Prevention

Q. Sandy in Villas, NJ writes: "My yard is small, so I trellis my delicious Honeynut Squash. I also plant my own saved seeds instead of using purchased plants; and this makes it hard for me to implement your suggestions for using barriers to keep away squash vine borers. I read that planting winter squash after July 4th greatly reduces the chances of encountering the bugs, but not why. Is late planting a viable alternative to physical barriers? Do you have any other useful ideas? I love your show and always learn something new!"

A. Thanks Sandy! But I doubt your timing trick would work against this Evil Insect. According to the Pennsylvania State Extension System, the moth behind the problem overwinters in the soil in a larval state (technically a pupa), TYPICALLY emerges mid-to-late June and lays her eggs in July and August, although locale and weather can dramatically change those parameters. An unusually warm season could move the egg-laying into June in our area. And of course, they're up and out earlier the further South you garden. In the deep South they could even have more than one generation.

Let's go through their life cycle: Adults emerge from the soil, mate and then the female goes looking to deposit her eggs on squash family plants that have hollow stems, like zucchini and pumpkins, right at the soil line. They don't lay their eggs on squash with solid stems; but they will sometimes lay their eggs on the stems of cucumber plants. The female is a day flying insect that looks a lot more like a weird wasp than any kind of moth, with translucent wings and an orange and black body. Pretty easy to spot, especially since they fly by day. Once she has sniffed out a good home for her children, she lays a cluster of eggs on the stem of the vine right where it enters the soil.

In a week to ten days, the eggs hatch, teeny-tiny caterpillars emerge, immediately eat their way inside the vine, and once inside, feed and grow unseen. Soon the plant starts wilting. If your squash plants look like they need water but your other plants don't, get down and look for a hole at the base of the stem with lots of caterpillar poop around it. Slit the vine open with a single edge razor blade, or even better, use an X-Acto knife, a small, sharp and very precise artist's blade that's positioned at the end of a sturdy metal rod; great for this kind of close work.

When you reach the caterpillar inside; well...you got a sharp object in your hand, right? It's get even time! Then carefully heap soil around the damaged part of the vine; if you caught the problem quick enough, it may recover and keep growing. Experienced gardeners typically try and prevent the initial incursion by wrapping medical tape or aluminum foil around the base of their transplants so that the protective covering is half-underground and half above. Just think about those little caterpillars trying to bite their way through foil; a lovely image if ever there was one!

Now if Sandy were to start her own seeds indoors, she could likewise protect her plants at the time of installation. Otherwise, two good options would be to spray the growing vines at ground level with a weekly dose of Bt, the old original organic caterpillar killer. As soon as the miniature munchers bite into a vine sprayed with Bt, they'll lose the ability to eat and soon die. (And yes, Bt is safe for everything that is not a caterpillar; AND it has to be a caterpillar chewing on your plants.) Although, in controlled studies, simply wiping that part of the plant with a clean damp cloth twice a week worked as well or better than any pesticide, chemical or organic, as the object was to simply wash the eggs off the vine before they could hatch. I'm thinking a high-powered water pistol would work well here. Kind of like a game of Whack A Mole with caterpillar eggs taking the place of the moles. Fun for the whole family!

I was also thinking of a version of a popular form of cutworm protection--take an empty soup can (with both ends removed) and push it a few inches into the soil around the sprout when it emerges, so the emerging leaves will soon cover the opening.

But no matter what you do, don't plant squash where you've had vine borer issues in the past. Because, if undetected, the borers inside your vines will grow fat and strong and drop onto the soil at the end of the season, where they will quickly burrow down to pupate and spend the winter, just waiting for Nature's que to begin the process once again.

So interrupt the cycle! As soon a squash plant comes down with advanced symptoms, rip it out and destroy the nasties inside the vine before they can escape. Then cultivate the soil in that spot to uncover any pests you missed before they can get down deep. Hungry birds should be more than happy to finish up. You might also want to repeat that cultivation in the Spring, just before planting (when birds are extra hungry for worm-like treats!).

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