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.