Squash Vine Borer

Hosts

Squash, zucchini, pumpkins, and gourds. Hubbard Squashes are the preferred choice for the borer, but it is less likely to attack Butternut Squashes. Melons and cucumbers are generally not vulnerable.

Damage

Damage caused by the squash borer is shown by a sudden wilt of the plant. The borer larvae attack the stems of the plants, usually in the lower three feet. The damage to the stems prevents water and nutrients from circulating, thereby showing a wilt. Where a squash borer enters a stem is marked by a hole with plant material sticking out. If a plant has wilted without the presence of borers, other causes can include root damage by beetle larvae or a bacterial infection.

Description

The adult stage is a moth that has the appearance of a wasp, with a mostly-black body with orange-red markings. Its hide legs are covered with black and orange hairs. Front wings are metallic green and the hind wings are transparent. The wingspan is 1 to 1 1/2 inch.

The pupae are brown and 5/8 inch long, within a cocoon of earthen black silk that is 3/4 inch long. <>The larval stage is a fat, grub-like caterpillar with a brown head and a wrinkled, white body. Fully grown, it is one inch in length.

The eggs of the squash vine borer are dull-red, flattened ovals, about a millimeter in diameter.

Larvae enter the stem of the plant at the base within a few hours of hatching from eggs. They feed inside the stem for four to six weeks.

Natural Control

• Destroy vines after harvest to destroy any larvae remaining inside stems.
• Plow the soil in the spring to destroy cocoons left over from last season.
• Cover the vines at plant joints to encourage growth of secondary roots, which can support the plant if the main stem is damaged.
• Borers can be removed successfully from vines if they are detected early. To do this, slit the stem with a sharp knife and remove the borer. Cover the stem wound with moist soil above the damage to promote root formation.
• Covering the stems with a barrier (e.g. nylon stocking strips) can prevent egg laying.
• Destroy the moths in twilight or early morning when they are resting on the upper side of the leaf bases.
• Pick off the eggs before they hatch.

Chemical Control

The squash vine borer can be killed by chemicals, but it is most effective at the time when eggs are hatching. To prevent infestation, apply an insecticide when vines begin to spread and reapply every week for three to five weeks. Apply the insecticide to the base of the plants.

Chemicals used for borer control in gardens are methoxychlor, rotenone, pyrethrum (Bug Buster), 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.

Cooper Seeds' Recommendation

Sevin-10 Bug Killer, 5 lb. bag. Kills 70 insects on vegetables, fruits and ornamentals.

Least Toxic Choice

References

Photo Credit: R. Bessin, Univ. of Kentucky Entomology

Squash Vine Borer, Ohio State University Extension Fact Sheet