Insect Note #20 (Revised)

Prepared by: K. A. Sorensen, Extension Entomologist

Dated 1/94
Placed on the Web 4/95 by the Department of Entomology, NCSU

The Squash Vine Borer

Melittia satyriniformis (Hubner) Lepidoptera: Sesiidae

The squash vine borer is a very destructive pest of squash and pumpkins in North Carolina. It is a native pest and is present east of the Rocky Mountains from Canada to South America. Borers also attack cucumbers and melons to a lesser degree.

Description of Injury

Damage first appears as a sudden wilting of a long runner or an entire plant. Closer examination reveals masses of coarse, greenish-yellow excrement which the borer has pushed out from the stem. Splitting the stem cap may reveal a thick, white, wrinkled, brown-headed caterpillar up to 1 inch long and almost 1/4 inch thick. In commercial squash plantings 25 percent or more of the crop can be damaged. Home plantings suffer even greater losses, as infested vines are often completely girdled and usually become rotten and die. Small borers may enter leaf stems but are most often found toward the base of the plant. Later on they may be found throughout the stem and even in the fruit. Sometimes vines are almost severed.

Life History

The adult is a "clear-winged" moth with metallic greenish-black scales on the front wings. The hind wings are transparent like those of a wasp.

Moths have a wing expanse of 1/2 inches. The abdomen is ringed with orange and black. They fly swiftly and noisily about plants during the daytime. Female moths lay their small, oval, somewhat flattened, brownish eggs on stems in May or early June. Young borers hatch in about a week, tunnel into stems, feed and are full grown in about four weeks. They have a brownish head, six short slender legs on the thorax (body) and five pairs of short prolegs (false legs) on the abdomen. Each proleg bears two transverse rows of crochets (curved spines). Larvae leave their burrows and make a cocoon in the soil. Two or three weeks later, adults emerge, giving rise to a second generation of larvae in North Carolina during early August. The insect overwinters an inch or two below the soil surface inside a tough, dirt-covered, silk-lined, black cocoon about 3/4 inch long, in either the larval or pupal stage.

Control

Once borers have gained entrance into stems, little control is possible; hence, early detection is critical. Excrement should be watched for around the bases of plants, and when first noticed, insecticide sprays should begin. Success of any insecticidal treatment depends on early and repeated treatment. Apply the spray to the stems near the base of the plant and repeat weekly during egg laying periods (early June and early August).

Cultural Control

Since the insect passes the winter in the ground, squash should not follow squash. Land should be disked in the fall to expose the cocoons and then plowed deeply the following spring. Vines should always be destroyed following harvest to prevent late caterpillars from completing their development.

Sometimes injury can be offset by late and staggered plantings and heavy fertilization to promote rapid growth. Planting early susceptible varieties as "trap crops" only serves as an indicator of squash vine borer's initial presence and that control practices should commence. Butternut 23 squash has some resistance to the squash vine borer. An egg parasite exists but fails to destroy borer eggs in most years. Hence, control at best, is marginal.

Commercial Control

Insecticide and Formulation Amt. Form/Acre Active Ingredient/Acre Min. Interval (days) between last application and harvest Precautions and Remarks
         

endosulfan (Thiodan, Phaser)

3EC
50WP



1qt
2lb

0.75lb
1bl

2
2		 Apply weekly to flower buds, stems, and vines beginning when moths first appear. Check vines in early June and August for borer presence. Do not exceed three applications per year.

estenvalerate (Asana XL) 0.66EC

4.8-9.6oz 0.03-0.05lb 3  
permethrin (Ambush) 2EC 6.4-12.8oz 0.1-0.2lb 1  
bifenthrin (Capture) 2EC 2.6-6.4oz 0.04-0.1lb 3   
 
Commercial growers should always check with their buyers and processors before using any pesticides. Consult the pesticide label for the latest information on safety, compatibility with other pesticides, rate and time limitations to harvest.

As most insecticides are toxic to honey bees and other pollinating insects, applications should be made in late evening and directed to the base of plants.

Home Garden Control

If only a few vines are present, keep a close check on them. Should any wilting occur, check the base of plants for signs of excrement and borer damage. If there is evidence of borer activity, remove the borer by slitting the vine with a sharp knife and removing the larva. Then cover the injured area with moist soil. Some gardeners put a shovelful of soil at one or more locations along each vine. This is to encourage the plant to develop a supplementary root system and thus overcome squash vine borer attacks at the base.

The following chemical control program gives good control if started at the very first sign of an infestation:
Insecticide and Formulation Amt. Form./Gal. Spray Min. Interval (Days) Between Last Application Precautions and Remarks
endosulfan (Thiodan) 50WP 2 tbsp. 0 Treat plants before first bloom. Repeat weekly intervals as needed. The base of the plant is the critical area. Borers are destructive in early June and again in August in most years. 

 
Note: Sevin is not effective against squash vine borers.

The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsements by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. All pesticide recommendations provided in this publication apply to pest control in North Carolina. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain information about product usage in your locale and examine a current product label before applying any chemical. The information presented on pest biology is based on conditions in North Carolina and may not be applicable to your locale. For further information, we recommend that you contact the Cooperative Extension Service office in your county.