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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. Young larvae hatch from dark reddish brown eggs and grow to about one inch long with a whitish body and brown head.


Squash vine borer larva


Adults emerge in late June and the first of July from overwintering cocoons in the soil and lay eggs on all plant parts except upper leaf surfaces. The majority of eggs are laid on the basal stem. 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 about two inches below the surface. There is one generation a year in northern and central Illinois and a possible second generation in southern Illinois.


Squash vine borer damage


The larvae bore into the stem and feed on tissue, hollowing out the vines. The majority of 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.


Non-chemical: In the spring, cover the plants with polyester row covers 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 attack. However, an early Fall may result in litle or no crop. Certain squash varieties offer an apparent resistance to and tolerance of borer attack. The chart below indicates the susceptibility of 12 varieties, with a rating of 5 indicating highly susceptible, while a rating of 1 indicates fairly tolerant.

Variety of Type Rating
Blue Hubbard (Hubbard type) 5
Boston Marrow (Hubbard type) 4
Golden Delicious (Hubbard type) 4
Connecticut Field pumpkin (ornamental type) 4
Small Sugar pumpkin (ornamental type) 4
Zucchini 4
White Bush Scallop 3
Acorn 3
Summer Crookneck 2
Dickenson pumpkin 2
Green Striped Cushaw 1
Butternut 1

Chemical: As soon as the vines begin to run, a weekly preventive treatment should be applied to the basal three feet of the plant. Contact your county Extension office for current pesticide controls.