How to Kill Squash Borers. The squash vine borer can be a serious pest in a garden with both summer and winter squash plants. Once the wasp-like, clear-winged insects are detected, control measures should be applied to prevent a serious infection and possible crop loss. The insects lay eggs that hatch into larvae, which bore into squash stems and feed on the pulp, blocking water flow throughout the plant and causing it to wilt. One generation hatches each year and feeds for four to six weeks before pupating in the soil, so it is important to plant new squash crops in different garden locations to prevent reinfection. Crop cycles along with chemical and physical control make management of this pest possible. These pests are found in the United States east of the Rocky Mountains and tend to thrive in hot weather.
Spray or dust the base of squash stems with insecticide if the borers are detected, or when the vine begins to spread. For bushing types, applications can begin in late June or early July. Use an insecticide labeled for use on squash, potato, or that is labeled for all vegetables. Common chemicals used include carbaryl, permethrin, bifenthrin and esfenvalerate.
Apply a second treatment of insecticide after seven to 10 days. Usually a second application will kill adults. Continuous treatments every seven to 10 days thereafter might be necessary for serious problems and can be continued through July.
Cut a slit in the stem of an infected plant if chemical efforts are not successful and if the plant is beginning to wilt. Make a cut up the vine until you find the borers. Stab the pests with the knife to kill them. Cover the cut area with moist soil and and provide plenty of water. The plant may continue to survive because new roots can grow from the cut, but this method should only be used if the plant is already suffering from the borer.
Remove any plants that have died from squash borers to prevent them from infecting additional plants.