Insect Pests

Here squash bug adults feed on the surface of pumpkin. - Whitney Cranshaw, Colorado State University, www.insectimages.org

These are squash bug nymphs at various stages of growth feeding on the underside of a leaf. - Whitney Cranshaw, Colorado State University, www.insectimages.org

Squash bugs damage squash and pumpkins by sucking sap and causing leaves and stems to wilt and collapse. Watermelon, cucumbers, and gourds can also be victims, but the bugs will go to squash and pumpkins first. Uninfested runners remain healthy while infested sections suddenly wilt. Squash bugs also spread a recently discovered bacterial disease called yellow vine decline that causes the whole plant to die; for this reason alone, they are important to control as soon as you set out squash transplants if the bugs have been present in the past.

Squash bugs appear in spring after wintering in garden debris, under old boards, in woodpiles--just about anywhere they can find shelter. They lay tiny, football-shaped, bronze eggs in clusters in the angles between veins on the undersides of leaves. These hatch into green and dark red nymphs that turn light gray and then brown as they age. They feed in groups on the leaves and vines and then move to the fruit.

The best way to prevent the pests is to clean up the garden. You can spray with Sevin or a pyrethrin product according to label directions. However, these insecticides kill bees, which are crucial pollinators of squash and its relatives, so you must spray cautiously. Begin spraying before the plants begin blooming to knock out many of the squash bugs early. If they continue to fly in from other places and if you must spray blooming plants, do so near dusk, after the bees stop their work for the day. Be sure to spray the undersides of the leaves because this is where squash bugs begin the attack.