Authors: PJ Liesch and Russ Groves, UW-Entomology
Revised:  01/30/2026
Item number:  XHT1136

The squash vine borer (Melittia cucurbitae) is an annual pest of cucurbit crops, including pumpkins and squash.  Squash vine borer activity can be spotty, but it can be occasionally cause significant damage.  Winter squash is highly susceptible to attack.

Appearance:  Squash vine borer adults are mid-sized, day-flying clearwing moths with a wasp-like appearance.  The forewings of the moth are greenish-brown while the hindwings are transparent with a fringe of reddish-brown hairs.  The wingspan of the adults is 1 to 1.5 inches.  The moth’s body is rusty orange with black bands on the abdomen.  The larvae (caterpillars) are pale-colored, with a segmented appearance, and a dark head capsule.  Larvae are up to 1 inch long at maturity. The caterpillars are the damaging life stage of this insect.

Symptoms and Effects:  Damage caused by squash vine borer larvae can easily be overlooked until infested plants wilt and die in late July and August.  The first symptom of feeding damage is when plants wilt midday.  This wilting is caused by larvae as they tunnel through vines and destroy the tissues that transports water.  Wilt symptoms may be confused with those caused by bacterial wilt or Fusarium wilt.  To distinguish between squash vine borer injury and these diseases, look for entrance holes near the base of wilting vines.  If sawdust-like frass (droppings) is present near the entrance holes, carefully split the stem lengthwise to confirm the presence of larvae.  Fields that have been damaged in the past are likely to be damaged again. Larvae boring into a main stem can kill an entire plant, while those boring into a runner will only kill the runners, and not cause economic damage in larger plants. 

Life Cycle:  Squash vine borers overwinter as pupae in the soil.  They emerge as moths in late June and July, when 900 Growing Degree Days (Base₅₀) have been reached.  This coincides with full bloom of the common roadside weed chicory.  Female moths lay small, brownish eggs at the base of plants.  Once the eggs hatch seven to 10 days later, the larvae immediately begin burrowing into vines where they feed for 14 to 30 days.  As larvae feed they leave behind a characteristic light brown frass (droppings) that resembles sawdust.  Fully grown larvae leave the plant to pupate in the soil.  There is one generation per year, although this insect has been documented attempting a second generation in slightly warmer areas.

Management:

Non-chemical management: Many non-chemical approaches can help manage squash vine borers:

• Plant selection: Susceptibility to squash vine borer varies amongst types and cultivars of cucurbits. Commonly infested cultivars are pumpkin (standard and giant), zucchini, as well as crookneck, straight neck, acorn, patty pan, summer, banana, buttercup, and Hubbard squashes. Choosing cucurbit crops that are less-susceptible to damage is one approach.
• Early planting: Early plantings tend to have fewer problems with squash vine borer than crops planted later in the season. Thus, shifting your planting date earlier could help prevent issues.
• Trap-cropping: Certain cucurbits (e.g., Hubbard squash) are known to be highly attractive to squash vine borers. Deliberately planting an attractive trap-crop can draw adult moths away from desired crops. The trap crop can then be destroyed while squash vine borer larvae are still within stems to kill them.
• Physical removal: Many cucurbit crops are surprisingly resilient and can recover from damage, if caught early enough. In small-scale plantings (e.g., home gardens), stems with active infestations (as indicated by frass) can be carefully split open so that the squash vine borer larvae can be physically removed. After removal of the borer, cover the affected stem portion with a mound of soil and keep it moist to encourage new roots to form.
• Row covers: When squash vine borer adults are actively flying and laying eggs, one option is to cover plants with mesh netting (e.g., row cover) to serve as a physical barrier. Keep in mind that plants that are flowering will need to have the netting removed for pollinator access.

Chemical management: Squash vine borer can be difficult to manage with insecticides since older larvae are protected within plant stems. Insecticides are generally sprayed onto the vines to target newly hatched larvae that have not yet tunneled into plants. Two to three insecticide treatments, spaced 5-7 days apart during the three week egg-laying period around 1000 Growing Degree Days Base₅₀ will control most of the larval borers before they burrow into vines and become protected by vine tissue. Treating plants with runners that are less than two feet long is particularly important.  Begin monitoring plants once 900 Growing Degree Days Base₅₀ have accumulated.

For small-scale settings (home gardeners), contact insecticides from the pyrethroid group (e.g., bifenthrin, cypermethrin, permethrin, etc.) or carbaryl can be used to prevent damage from squash vine borer.

For commercial production, refer to the UW-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for a list of registered insecticides and management recommendations.

Thanks to Karen Delahaut (formerly UW-Madison Fresh Market Vegetable Program) for work on earlier versions of this document.

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