Squash bug is one of the more difficult insects to control on vegetables. It is a common pest of squash, pumpkin, and zucchini. This bug extracts plant juices with its piercing-sucking mouthparts and potentially transmits the pathogen that causes yellow vine decline. In Kentucky, we have one or two generations of this pest each year, depending on seasonal temperatures.
Squash Bug Biology
Squash bug overwinters as an unmated adult and begins to colonize fields in late May or early June. While we typically don’t see overt signs of damage from overwintering adults early in the season, this is one of the stages that needs to be controlled. By mid-June, they begin laying eggs on upper and lower leaf surfaces; eggs will hatch in about a week. Young nymphs are initially green with black legs, but soon turn gray as they produce wax to cover their bodies. As these nymphs get older, it gets more difficult to control them with insecticides because it takes a larger dose to kill them, the plants become much larger making thorough coverage with sprays more difficult, and the larger nymphs and adults tend to be found in the lower parts of the plants. For these reasons, early effective control of squash bugs facilitates better season-long control.
In terms of threshold for control, an average of one adult per 2 plants or an average of one egg mass per plant can be used to determine the need for sprays. While one egg mass per plant is used as the threshold, sprays need to be timed to coincide with egg hatch. As nymphs are found on flowering plants, it is important to spray late in the afternoon when flowers are mostly closed and pollinator activity is low. With conventional insecticides, pyrethroids and neonicotinoids are among the most effective, while for organic growers a mixture of pyrethrin and azadirachtin or spinosad are the most effective.
Ric Bessin Extension Entomologist