Squash Vine Borer

The squash vine borer tunnels in the vines of pumpkins and summer and winter squash; it rarely is found in cucumbers or melons and cannot complete its development except in squash or pumpkins.

Identification.  The squash vine borer adult is a black and reddish moth called a clearwing moth because large portions of its hind wings lack scales.  These moths are ¾- to 1-inch long, with a 1- to 1 ½-inch wing span.  They are active during the daytime and superficially resemble wasps as they fly about.  Larvae are yellowish-white with a brown head, 3 pairs of thoracic legs, and 5 pairs of fleshy abdominal prolegs that bear tiny hooks called crochets.  Fully-grown larvae are about 1 inch long.  Brownish pupae are slightly less than 1 inch long, and they are found in the soil inside a dark, silken cocoon.

Life Cycle.   Squash vine borers overwinter as mature larvae or pupae within cocoons 1 ½ to 3 inches below the soil surface.  Moths emerge and begin to mate and lay eggs in June and July in much of the Midwest (earlier, beginning in May, in southern Illinois and similar latitudes).  Moths lay eggs singly at the base of plants or on stems and petioles, beginning when plants start to bloom or "run".  Larvae feed within stems or petioles for 2 to 4 weeks, leaving brown, sawdust-like frass (droppings) at holes where they entered the stem. In southern Illinois these pupate and produce a second flight of moths in late summer; in the north, larvae or pupae of the first (and only) generation remain in the soil through the winter.

Plant Injury. Tunneling within vines destroys water- and food-conducting tissues, reducing plant vigor and yield and sometimes killing vines.

Management.  Disking or plowing to destroy vines soon after harvest and bury or destroy overwintering cocoons reduces moth populations within a field in the spring.  Staggering plantings over several dates also allows some plantings to escape heaviest periods of egg-laying.  Early detection of moths and initial damage is essential for timing insecticide applications.  For insecticides to be effective, they must be applied before larvae enter stems or petioles.  Scout for moths (pheromone lures and traps are available for monitoring flight periods but are not consistently effective for detecting moth flight) and look for entrance holes and frass as soon as plants begin to bloom or vine.  Apply insecticides beginning 5 to7 days after moths are first detected and at weekly intervals for 3 to 5 weeks, or begin when injury is first noted and make a second application a week later.  See the 2014 Midwest Vegetable Production Guide for Commercial Growers for listings of registered insecticides.

(from Illinois Fruit and Vegetable News, Vol 20 No 7)