Squash Vine Borer Control
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Question. I am a 99% organic gardener, and as I prepare for another summer, I wonder if there are any new ways to combat vine borers; they are a common problem down here, and always get my zucchini vines. I have used row covers, injected the vines with BT, and even used a butterfly net to try and catch the adults as they fly around the garden. But they are smart and hard to catch; I think they know what 'a guy with a net' means!
- ---Manuel in Austin, Texas
- ---Emily in Salisbury, Maryland
- ---Sharon in West Chester, PA
This is an especially nasty pest because the 'borer', a grubby white caterpillar, hides inside the hollow vines of popular squash-family plants like pumpkins and zucchini as it does its dirty work. Gardeners generally don't notice anything is wrong until the whole plant starts wilting, and by then, it's generally too late. So we will focus here on prevention; don't blame us if you end up with too much zucchini.
The problem begins in late Spring, when a moth lays its eggs at the base of your squash plants. Each female will lay about 200 eggs, but one at a time rather than in clusters, making the tiny eggs (a mere 1/25 of an inch long) almost impossible to spot. They hatch in a week or two, and the little caterpillars that emerge quickly tunnel into the hollow plant stems their eggs were so cleverly attached to. The caterpillars feed, hidden from view, for a month or so and then drop down into the soil to pupate. In the North, they emerge as adults the following Spring. Down in Manuel's Texas, the first run pupates quickly into adults, whose children commit another round of squash vine damage before they drop down into the soil for the winter.
That's means they're in your soil right NOW. If you had borer damage last year, you probably have hibernating baby borers lurking in your dirt; just like the pods in Invasion of the Body Snatchers (don't fall asleep in the garden!). Before you plant anything this season, use a hoe to cultivate the soil where your squash grew last year; look for cocoons an inch or so deep. If you find some, well…just make sure no one is watching and try not to sound too much like The Joker after he's captured Robin the Boy Hostage again.
One way to avoid the adult moth—which looks like a little red-bellied wasp—is to cover your squash plants with floating row covers; these spun polyester fabric blankets (best know brand name: Reemay) allow water, light and air through, but prevent bugs of all kinds—including bees, which is a problem. If you go this route, make sure you plant where squash didn't grow the previous year (or the moth may emerge inside the row covers—eeek!) and either grow self-pollinating varieties or lift the covers and pollinate the flowers yourself with a little paintbrush. In one-generation climes, you can remove the covers entirely by the Fourth of July; all the egg-laying action will be over.
An interesting variation on this technique is to cut little pieces of row cover and use them to just wrap the vine itself. Do this before you plant, so that the covered section of the vine extends below the soil line; and add more wrapping as the vine grows larger.
But the most reliable cure may be to grow your squash out in the open and use vigilance to get the eggs. You may not be able to see them, but a weekly spray of the vine with insecticidal soap will smother them nonetheless (use a commercial product, not home-made; there is a fine line between beneficial soap and plant-killing herbicide).
Or use BTK. This is where I assure worried Emily that BTK is indeed organic and non-toxic; one of the oldest organic pest controls, in fact. Sold under brand names like Dipel, Thuricide and Green Step, this form of Bt ONLY kills caterpillars that munch on the sprayed plant part; it affects nothing else. So spray the vines once a week and there will be BTK on the stem when that hungry, hungry caterpillar comes out and starts munching.
Or just wipe the stems every five days vigorously with a damp cloth and wipe away the eggs. An Auburn University researcher found this tip in a farming book from the 1890's, when even now-ancient remedies like BT were still half a century in the future! Wiping with BTK or insecticidal soap should be even better.
Once the season is underway, carefully inspect each vine once a week; don't wait for wilting! If you see a hole near the soil line and that distinctive greenish frass (bug poop) that the borers push back out of their comfy new home, slit the vine with a razor blade and find the caterpillar inside. We will now flash forward to you later heaping compost-rich soil over the damaged part of the vine. (Remember—no laughing like The Joker!)
Or inject the attacked vine with BTK. Or beneficial nematodes; these microscopic garden helpers love to prey on tasty caterpillars, and the moist inside of the vine will protect the nematodes as they go a hunting. You'll find garden syringes sold for injecting nematodes and BTK at some garden centers and by mail order.