There are pesticides that can be used to help control the squash vine borer. However, their effectiveness leaves much to be desired. The problem is that when the eggs of this critter hatch, the larvae immediately start to bore their way to the inside of the stem. Once they are there, little can be done as the pesticide cannot reach them. See the Ohio State University article on the squash vine borer located at this Web site:
www.ag.ohio-state.edu...
This, in part, is what it says about control: Cultural Control - Destroy vines soon after harvest to destroy any larvae still inside stems. Disk or plow the soil in fall or spring to destroy overwintering cocoons. Cover vines at leaf joints with moist soil, to promote formation of secondary roots that will support the plant if the main root and stem are injured. A trap crop of very early-planted Hubbard squash can be used to alleviate pest pressure from other cucurbits.

Physical Control - The following are suitable in small plantings: Borers can be removed from vines if detected before much damage is done. Examine stems in early summer; once holes are detected, slit the stem longitudinally with a fine sharp knife, remove the borer, then cover the wounded stem with moist soil above the point of injury to promote additional root formation. Stems can be covered with a barrier, such as strips of nylon stockings, to prevent egg laying. Catch and destroy the moths, especially at twilight or in early morning when they are resting on the upper side of leaf bases. Hand-pick the eggs before they hatch.

Chemical Control - Squash vine borer can be killed by chemicals but the trick is in the timing of the application. An insecticide is effective when applied at the time that eggs are hatching. A preventive treatment regime is to apply an insecticide when vines begin to run, and re-apply every 7 to 10 days for 3 to 5 weeks. The application should be directed to the base of plants, at crowns and runners. Chemicals used for borer control in gardens are methoxychlor, rotenone, pyrethrum, Malathion, or carbaryl (Sevin), applied as sprays or dusts. Restricted-use insecticides used for borer control by commercial growers include endosulfan (Thiodan) and pyrethroids (Ambush, Asana, Pounce). The biological insecticide B.t., in the forms currently available, is not effective because it cannot be applied to the plant parts that are eaten by the borer.