Squash bugs, or Anasa tristis, are a common garden pest throughout North America. They feed on young cucurbit plants, favoring pumpkins and squash over cucumbers or other vining plants. These destructive bugs may overwinter in garden debris, emerging in the spring to feed off young plants and lay their eggs. Squash bugs are difficult to control once they infest a garden. Because they can overwinter in plant debris, squash bugs may occupy a garden for several seasons.
Squash bugs are dark gray or black in color and measure approximately 5/8 inch long and 1/3 inch in width. The backs of these bugs appear flat and may be have small yellow speckles. These six-legged bugs resemble stink bugs and also give off an unpleasant odor when their bodies are smashed.
Squash bugs lay their eggs on the undersides of leaves of squash plants. Eggs are laid in v-shaped clusters near leaf veins. The emerging nymphs may resemble white or light gray spiders, though their bodies are more oblong and they have the six legs rather than eight.
Little can be done to prevent squash bugs from coming into the garden if vining plants are present. Because they overwinter under rocks and debris, a preventative approach is to clean out the garden of possible hideouts when winterizing the garden. This does not, however, prevent the squash bugs from entering the garden in the spring from other areas.
Squash bugs emerge in early spring as the temperatures warm. Setting out seedlings just after the first frost attracts the bugs, giving the gardener opportunity to quash the population early in the season. The eggs may be squashed by hand and adult bugs squashed. Another form of trapping is to set out the early plants and place boards or shingles around the plant. The adults gather on the underside of the makeshift shelters at night. Early in the morning, the gardener flips over the boards or shingles and smashes the bugs en masse.
At the first sign of infestation, pesticides that include permethrin or carbaryl as active ingredients may be applied directly to the plants and the soil surrounding the plants. Due to the high number of eggs produced by squash bugs, more than one application of insecticide is likely needed to maintain control.
The flowering herb nasturtium gives a scent that repels squash bugs. Planting these around squash plants in succession throughout the season may drive away squash bugs. Tansy, another herb, is recommended as a deterrent to squash bug infestation. As an addition to these plants, laying down a thin layer of diatomaceous earth around plant bases also discourages squash bugs. Diatomaceous earth granules, made from fossilized shells, are sharp-edged and cut the outer shells of bugs, resulting in their deaths. The squash bugs retreat from the treated areas.