From Organic Gardening: Squash bugs are grayish brown bugs up to 3⁄4 inch long; nymphs are similar, but do not have wings. Feeding by adults and nymphs causes leaves to wilt and blacken. Hand pick them and drop them in a container of soapy water. Also destroy their red-brown egg clusters on the undersides of leaves. To trap adults, lay boards on the soil at night; the squash bugs will tend to congregate beneath them, and you can destroy the pests the next morning. Planting radishes, nasturtiums, or marigolds among your squash plants may help repel squash bugs. If plants are heavily infested with young squash bugs, try spraying insecticidal soap.