Squash bugs are a nuisance to farmers and gardeners alike. Squash bugs are an insect in the family Hemiptera, referred to as the “true bugs,” and have straw-like mouthparts to pierce the plant, inject digestive enzymes, and suck out sap. Squash bugs damage cucurbits by sucking sap from their leaves, stems, and young fruits, weakening the plant. Older plants can typically recover from the damage, but younger plants can be severely damaged or die. Squash bugs prefer to feed on squash and pumpkins, but they can damage any cucurbit crop.

In addition to the damage caused by their feeding, squash bugs also transmit the bacteria that causes cucurbit yellow vine disease. This damaging disease can quickly spread through an entire field and kill the plants shortly before the crop is ready to harvest. Cucurbit yellow vine disease is caused by the bacterium Serratia marcescens. The symptoms are similar to those of bacterial wilt, with the plant leaves first yellowing and then wilting entirely. Since squash bugs prefer squash and pumpkins, CYVD is more common in these crops. Learn more about squash bugs and cucurbit yellow vine disease with this video and infographic from the Current Cucurbit project.

To avoid damage from the squash bug and cucurbit yellow vine disease, you should regularly scout your fields to identify this pest. The adult squash bug is about 1” long with a mottled brown appearance. It is commonly mistaken for a stink bug, but is narrower than stink bugs in the Midwest. It has a distinctive darkened triangle at the end of its abdomen formed by the wings, and a brown and white checkered pattern around the edge of the abdomen. In addition to adults, it is important to look for the nymphs and eggs of squash bugs and destroy them. The eggs are small copper-colored ovals, and typically occur in clusters on the top or underside of leaves. Once the eggs hatch, the nymphs emerge, which are initially green with black legs but soon appear as small grey miniature versions of the adult squash bugs. They also often appear in clusters on the top or bottom of leaves, as the youngest ones don’t stray far from the eggs. As the nymphs get older, they appear more and more similar to the adults. Check both above and under the leaf canopies and vines to find the eggs and nymphs. Females continue laying eggs over a long period of time, so it is important to control them early to prevent the population from continuing to grow.

Image 2. Egg cluster (L) and a nymph (R) of the squash bug. Photos by Lexi Gauger.

Squash bugs may be easily confused for another common pest, the brown marmorated stink bug (BMSB). The BMSB is very similar in coloration, but has identifying features that distinguish it from the squash bug. Stink bugs have a shield-shaped body which is less oval-shaped and elongated than the squash bug. The wing overlap of the BMSB is white instead of brown, and the checks along the edge of the abdomen are brown and black. Nymphs of the BMSB are usually more green in color and the eggs are a pearly white color instead of the copper color of squash bug eggs. Stink bugs can also damage cucurbit plants, but do not transmit diseases and do not specifically target cucurbits.

Locating and identifying squash bugs, both as adults and in their nymphal and egg forms, is very important to monitoring the health of your cucurbit crop. Squash bugs have a low economic threshold since their populations can rapidly grow. The general guideline is that if there is one or more egg mass per plant, or one or more adult per plant, treatment action should be taken. Catching a squash bug problem early can help prevent a population explosion later in the season, and can help you avoid the damaging effects of the cucurbit yellow vine disease. If early-season applications are needed, spray coverage is much easier before extension vine growth and leaf density interferes with spray penetration.