The Prettiest Garden Pest

Late June, 2002

Many of us in the southern Appalachians are watching with delight as our tiny garden plants finally begin to take off. Now, at last, they seem to be responding to our care, safely outgrowing the pests that have threatened to devour them. The late frosts are finally past, the cool mornings are gone, and the garden seems unstoppable. Right now, however, the loveliest, but most insidious of garden pests arrives: the squash borer moth.

These moths lay copper-colored eggs on the stems of squash plants just above the level of the ground. The eggs are not easy to see, but look like a row of tiny b.b.’s on the green stems. In only a few days, the eggs hatch and the hungry caterpillars cut their way into the center of the stem. There the caterpillars live, safe from predators and from pesticides. They eat the heart of the squash stem, eventually killing the entire plant. A little pile of sawdust-like feces oozing from a hole in the stem is all you’ll see.

You mostly don’t know that your squashes harbor the caterpillars until it is too late. If you catch them early enough, either split the stems lengthwise and remove the worms, or ram a piece of wire into the hole and skewer them. The squash stem will heal, and if covered over with soil, it will sprout more roots. Unfortunately, once the plants are wilted and dying because of the feasting caterpillars, there isn’t much you can do. Prevention is the only medicine.

The adult moths are present for just a couple of weeks in late June, sometimes lingering into early July. Some people cover their plants with row covers during this time so that the moths can’t get to the plants. However, this also prevents honeybees or other pollinators from pollinating the flowers. Others use organic pesticides such as neem, pyrethrin, or rotenone to dust the bases of the plants, which is also a bit of a trick. Those same pollinators are killed by pesticides just as effectively as the squash borer. Still others pile soil around the plants right up to the first true leaves, which discourages, but doesn’t prevent, the moths from laying eggs. A daily spritzing of the squash stems with soapy water will kill the eggs and is also a great way to kill aphids on other plants without harming pollinators. If you must use pesticides, only apply them in the late evening after the blooms have closed.

If your zucchini, pumpkin, and yellow squash plants died last year, be on the look-out for the moths. They less often bother butternut squash, cucumbers, or melons because the stems are small and hard.

The moth itself is beautiful—hardly the picture of devastation! Almost all the moths whose larvae are borers are clear-winged moths. You can actually see through their hind-wings! Squash borers are about an inch long. They have brightly-colored, orange and black, furry tufts on their bodies and legs. They fly low and very fast. The clear wings, bright colors, size, and flight pattern make them look like wasps instead of moths.

So if you see pretty wasps visiting your squash plants in late June and early July, look a little closer. They might be the beginning of the end of your squash plants! Catch and destroy any adult moths, and protect your plants. If your plants are severely infected, pull them up and either burn or crush them flat to kill the larvae. Check daily for the eggs on the stems, and Good Luck!

Photo: Devastation for squashes, the inch-long squash borer moth. The hind-wings are transparent, and the last pair of legs is covered with orange and black fur.

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