Squash Bugs: What They Do And How To Beat Them

Squash bugs (Anasa tristis) are a common pest of the home vegetable garden and you’ll see them attack all members of the curcurbit family: squashes, pumpkins, melons and cucumbers. They seem particularly fond, though, of certain squashes and pumpkins.

At first, they’re secretive little insects and it’s hard to spot them in the garden. They hide under big leaves, old pieces of wood or other debris, laying their tiny orangy-brown eggs and sneaking out to feed on foliage. The first symptom is often the unexplained wilting or browning of a leaf. Not only are the insects sucking vital plant fluids from the leaf, they have a toxic saliva that causes a diseased appearance in the leaf. They can also carry viral diseases that affect curcurbits. It’s common to see damage to just a portion of the plant but sometimes the wilting and browning is more widespread. The end result is similar to the damage caused by squash vine borers, but there is usually no stem damage with squash bugs.

Squash Bug Nymph 2

You can see the piercing mouthpart of this nymph, even though he is shyly turning his head away from the camera.

Squash bugs seem to be more a problem on big, well-adapted plants that got started early in the season. But I’m not going to stop planting squash early. That’s one way to avoid problems with the vine borers! Here are some tips to controlling the squash bugs.

•   Be a relentless scout early in the season. Observe young plants (from up close!) every day, looking for the orange or brown egg masses. Vacuum them up or swipe them off, thus preventing the eggs from hatching into hungry little nymphs.

•   If that fails, watch for the light grayish-brown nymphs. It’s easier to control them than it is to control their more mobile adult counterparts. The nymphs are gregarious, meaning they like to hang out in big groups. Use that to your advantage: you can wipe out an entire neighborhood with a paper towel and a steely resolve.

•   Some gardeners leave boards in the garden on purpose to trap groups of shy nymphs or to entice the adults to lay eggs there, where it’s easier to wipe them out. A strong jet of water will do it, but if you’re not squeamish, you can squish them with the aforementioned paper towel.

•   Down here, we can easily get two or three generations of squash bugs and adults do overwinter in garden debris. After the harvest, clean out the garden. Take all squash-related leaves and stems to the compost pile. You don’t want to have any little hiding places for next spring’s advance guard.

•   Squash bugs are parasitized by a fly that lays her eggs in the body of large nymphs or adult squash bugs. Support her efforts by not using broad-spectrum, general purpose insecticides in the garden. Besides, it’s hard to control squash bugs anyway with insecticides. They tend to congregate down low in the base of the plants, where it’s hard to get them. Even the strongest insecticides (which are toxic not just to beneficials like this parasitoid fly, but honeybees as well) aren’t really more effective than treating with a “softer” product like neem oil or insecticidal soap and hand-picking.

•   If you use neem or insecticidal soap, take a few precautions. These products only really work on young, small nymphs. If you see larger ones, or egg masses, remove them by hand. Both neem and insecticidal soaps require complete coverage. You’re going to really have to dig down into the crown of the plant to drench the nymphs with the liquid. Also, in extremely hot weather, any sort of oil or soap can have a detrimental effect on leaves.

Your best bet is this little warrior below! So don’t be alarmed when you see what looks like a housefly-sized wasp buzzing around your flowers. When she’s young, she’ll feed on nectar but when she’s ready to lay eggs, she’ll help you by seeking out  your squash bug foes.

Parasitoid Fly, photo by Marvin Smith via Wikimedia Commons, under Creative Commons License

Parasitoid Fly, photo by Marvin Smith via Wikimedia Commons, under Creative Commons License

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