Squash Vine Borer

• Sudden wilting of a squash vine despite adequate moisture — often overnight
• Sawdust-like frass (greenish-yellow) oozing from holes at the stem base
• Entry holes at the base of the main stem, often near the soil
• Soft, hollowed-out stem when you cut into the damaged area
• The plant may recover if vines re-root, but often collapses entirely

The adult is a clearwing moth that resembles a wasp. It emerges in late spring to early summer and lays flat, reddish-brown eggs singly at the base of squash stems. Larvae bore into the stem and feed internally for four to six weeks, then drop to the soil to overwinter as pupae. There is typically one generation per year in the North, two in the South.

1. 01Cover stems with row cover from transplanting until the first female flowers appear; remove for pollination
2. 02Wrap the bottom 6 inches of main stems in aluminum foil to prevent egg-laying
3. 03Monitor for eggs starting in late May — small, flat, brown discs on the stem base. Remove them by hand
4. 04Inject Bt into infested stems with a syringe as soon as you find frass — timing is critical before the larva moves deep
5. 05Mound soil over nodes along the vine so it can re-root above the damage
6. 06Plant a second succession of squash in midsummer so new plants miss the main egg-laying window
7. 07Butternut squash tends to be less susceptible than zucchini or acorn

If vine borers have hit hard for two or more seasons in a row, an extension advisor can help you time plantings precisely to your local moth emergence window — this varies significantly by region and year.

• Squash Vine Borer— University of New Hampshire Extension
• Squash Vine Borer Management— Clemson Cooperative Extension