The squash bug, Anasa tristis, primarily attacks squash and pumpkins but can also attack other cucurbits, such as cucumbers. These bugs feed on plant foliage using mouthparts that let them pierce the foliage and suck plant sap. This results in plant wilt and in some cases plant death.
Adult squash bugs are somewhat flattened, large, dark gray to dark brown insects about 5/8 inch long and 1/3 inch wide. The edges of their abdomens protrude beyond their wings and typically have alternating orange to orange-brown stripes. If necessary, turn squash bugs over to better identify them. The overlapping structure of the wings on the adult makes and X in the center of the insects back. Note that when these insects are crushed, they give off an unpleasant odor. Don't confuse Squash Bugs with the Squash Vine Borer which also can attack cucurbits.
The eggs are yellowish to bronze elliptical shapes usually found in clusters of 15-40 on the undersides of leaves between the forks of the veins. Nymphs hatch 1 to 2 weeks later and are wingless, spiderlike and often covered with a whitish powder. Nymphs are approximately 1/8 inch long with a red head, antennae, thorax and legs and a green abdomen. This color fades with age to a gray/white with black legs and antennae. Nymphs molt several times into increasingly larger nymphs before becoming adults. This process takes 4 to 6 weeks.
The best method for control is prevention through sanitation. Remove old cucurbit plants after harvest. Keep the garden free from rubbish and debris that can provide overwintering sites for these insects. During the growing season, pick off and destroy egg masses as soon as you see them. Use protective covers where squash bugs have been a problem in the past, but remove the covers at bloom to allow for pollination. Consider planting resistant varieties to minimize damage. Squash bugs are difficult to kill using insecticides because the bugs are often hidden near the crown of the plant and difficult to reach with sprays. Neem oil, horticultural oil and canola oil are most effective on the smallest nymphs. If you suspect squash bug damage but are having difficulty finding the bugs, you can attempt to sample for the insects by placing an old wooden board in the garden. On cool nights, the board will attract squash bugs to spend the night under these structures so that they can be captured and eliminated the next morning.
Last updated April 5, 2018