SQUASH VINE BORER

a. Moth (or adult) with wings spread; b. moth with wings partly folded; c, part of squash stem (enlarged) cut open to show borer (or larva) feeding within; d. pupal cell in soil cut open to show pupa (or resting state) inside; e, part of squash plant showing typical appearance of wilting caused by feeding of squash vine borer inside the stem. (a, c, and d, about one and one-fourth times natural size; b, about two-thirds natural size; e, about one-third natural size.)

SQUASH VINE BORER

A gardener might discover one morning that his squash vines have wilted suddenly. Usually the wilting is due to the squash vine borer, a caterpillar that bores into the stem near the ground. Its presence may escape notice until piles of yellow, sawdust-like excrement, which falls from holes in the stem, become evident.

The adult is called a clear-winged moth because the hind wings are transparent, like those of a wasp. The female moth lays eggs on the stems in June or July in the North and in April and May in the South. The minute young larvae, or caterpillars, on hatching from the eggs, bore into the stem, grow rather rapidly, and are full-grown in about 4 weeks, when they are about 1 inch long. There is one generation a year in the North, two in the South, and a partial second generation in intermediate regions. The winter is spent in the soil as mature larvae or as pupae.

When the borers are numerous they cause severe injury. They bore throughout the interior of the stems near the base and may travel up the stems, even to the petioles of the leaves. Sometimes vines are almost severed. The fruits are sometimes attacked. As the larvae become larger the excrement, which is pushed out of holes in the stems, becomes visible. While most serious on squashes, especially the Hubbard, the borers also attack pumpkins, cucumbers, gourds, and other cucurbits.

Control: Although control is difficult, insecticides have been helpful. Apply a dust containing 1 percent of rotenone to the stems and basal parts of the vines three or more times at 10-day intervals. A spray composed of 1 part of 40 percent nicotine sulfate to 100 parts of water has been reported as effective in reducing infestations.

Apply the spray to the stems near the base of the plant and repeat the application at least weekly during the egg-laying period.

The success of any insecticidal treatment depends on early and repeated treatment, because after the young larvae have reached the inside of the stem the insecticides will not affect them.

The practice of covering the stems with soil to induce rooting beyond injured portions has long been followed with success, especially on heavy soils in humid areas.

After the borers have entered the stems and their presence becomes evident, the only known remedy is to slit the stems lengthwise with a thin knife or razor blade and remove the borer. The injured part should then be covered with soil.