Squash Vine Borer
Pest · Commonly affects: Zucchini and summer squash, Winter squash, Pumpkins, Hubbard squash, Gourds
The squash vine borer is the larva of a wasp-mimicking clearwing moth (Melittia cucurbitae) that tunnels inside the stems of squash and related crops. Because the damage happens hidden inside the vine, a healthy-looking plant can wilt and collapse within days, which makes this one of the most frustrating pests for home gardeners across the eastern and central United States.
How to identify it
The adult is a day-flying moth about half an inch long that is easily mistaken for a wasp, with metallic greenish-black forewings, clear hindwings, and an orange abdomen dotted with black. The larva itself is rarely seen because it lives inside the stem; it is a fat, wrinkled, cream-colored grub with a dark head. The surest sign of an infestation is a mushy hole near the base of the vine oozing moist, sawdust-like greenish-orange frass, usually paired with sudden wilting of an otherwise vigorous plant.
Damage
Larvae bore into the main stem near the soil line and feed on the inner tissue, choking off the flow of water and nutrients to the rest of the plant. This causes the vine to wilt abruptly, and heavily tunneled stems rot and collapse, often killing the plant just before or during fruiting.
Prevention
Rotate cucurbits to a different part of the garden each year and clear out and destroy spent vines after harvest, since the borers overwinter as pupae in the soil where the crop grew. Choosing solid-stemmed types such as butternut and other Cucurbita moschata varieties helps, because they resist tunneling far better than the hollow-stemmed zucchini, Hubbard, and pumpkin types. Give plants room for good airflow and grow them in healthy, well-drained soil so vigorous vines can outgrow early feeding and root along their nodes.
How to manage it
Cover young plants with floating row covers from planting until the first female flowers open, then remove the covers so bees can pollinate. Scout the stem bases weekly for the small, flat, reddish-brown eggs and rub them off by hand, and mound moist soil over the lower stem and leaf nodes to encourage backup rooting. If a borer is already inside, slit the stem lengthwise with a clean blade, lift out the grub, and bury the wounded section in damp soil so it can re-root; pull and destroy any collapsed vines promptly to break the cycle, and support natural parasitic wasps by keeping flowering plants nearby.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.