Squash Vine Borer

The adult squash vine borer is a colorful moth, 5/8 inch long with orange and black legs. The hind legs are heavily fringed with orange and black hairs. The adult may be mistaken for a wasp in appearance and flight. The front wings are metallic green, and the  hind wings are transparent. Young larvae hatch from dark reddish brown eggs and grow to about one inch long with a whitish body and brown head.

Squash, zucchini, pumpkins, and gourds are attacked by the squash vine borer. Hubbard squash is preferred over other hosts; butternut squash tends to be less susceptible than others. Cucumbers and melons are usually not attacked.

Life Cycle

Adults emerge from late June to the first of July from cocoons that overwintered in the soil and they lay eggs on all plant parts except upper leaf surfaces. Moths are active for about one month. After 9-14 days, hatching larvae usually bore directly into the stem and feed internally for about 4-6 weeks, though some may feed externally prior to entering the stem. At the end of this period, larvae enter the soil and spin a cocoon. There is usually one generation per year, but a partial or complete second generation is possible.

Damage

The larvae bore into stems and feed, hollowing out the vines. Most larval activity will occur at the basal four feet of vine. Plants wilt and usually rot and die beyond the point of attack. The first indication of an attack will be the sudden wilting of a long runner or of the entire plant. Upon close inspection, frass may be found extruding from the infested stem. Partial or complete crop loss may occur.

Control

The squash vine borer is most susceptible to natural enemies in the egg stage: the  eggs are commonly attacked by parasitic wasps. Larval and adult ground beetles can attack the larvae of the squash vine borer, but do not appear to cause significant mortality.

Non-chemical:

• In the spring, cover plants with row covers or other barrier until blooming starts to protect from egg laying moths. A second crop of zucchini or other summer squash can be planted in early July to avoid borer attach. Certain squash varieties offer an apparent resistance to and tolerance of borer attack.

• If detected, remove borers from vines before much damage is done. Examine stems in early summer; once holes are detected, slit the stem longitudinally, remove the borer, then cover the wounded stem with moist soil above the point of injury to promote additional root formation.

• Catch and destroy moths, especially at twilight or in early morning when they are resting.

• Hand-pick eggs before they hatch.

Chemical: The squash vine borer can be killed by chemicals, but appropriate timing is crucial. An insecticide is effective when applied as eggs are hatching. As soon as the vines begin to run, a weekly preventive treatment should be applied to the basal three feet  of the plant; re-apply every seven to ten days for three to five weeks. The application should be directed to the base of plants, at crowns, and at runners. Chemicals used for borer control in gardens include pyrethrum, malathion or carbaryl (Sevin).

Adapted from the Ohio State University Extension, 1999