Each year vine crops, including squash, zucchini and pumpkin plants, fall victim to squash vine borer larvae feeding inside their stems. The feeding often goes unnoticed until the plants begin to have yellowing, wilting leaves or sawdust like powder being produced near the base of the plant (Figure 1).
Squash vine borer adults belong to the clear-winged moth family (Sesiidae). These moths are often confused with wasps or bees due to their coloration and their clear wings.
The squash vine borer moths are approximately 1/2 of an inch long. They have an orange abdomen with a black spot on the top of each abdominal segment. The front pair of wings (closer to the head) are metallic green while the hind wings are clear. The antennae have a white band and the legs have similar white banding (Figure 2).
The larvae of the squash vine borer are cream colored with a dark brown head and dark brown pronotum (segment directly behind the head). The larvae will also have dark spots on each segment of their body (Figure 3). They are commonly found near the base of the plant inside the stems. Their feeding will result in a sawdust-like material being pushed out onto the stem, leaves, or surrounding soil.
The female squash vine borer moths lay eggs on the stem of vine crops near the soil surface. The eggs are flattened and reddish brown in color (Figure 4). Each egg is approximately 1/30th of an inch in diameter.
Squash vine borer adult emergence occurs in late June through early July. They are good fliers, so they can travel long distances. Unlike most moths, the squash vine borer adults are active during the day instead of night.
After emergence, the female moth will lay eggs at the base of plants. The eggs soon hatch, and the larvae bore into the stems to feed. The larvae will feed within the stem, which blocks water and nutrient flow to the rest of the plant, resulting in wilting. The squash vine borer larvae will feed for 4-6 weeks before exiting the stems and pupating in the soil.
Monitoring for adult squash vine borers may allow for management before the plants become infested. The moths are similar to wasps and are noted for making a “buzzing” sound while flying. A homemade bait trap made from a yellow container filled with soapy water can be used to monitor and reduce adult populations. There are also commercial pheromone lures available, which can be an option for larger scale operations.
Once adults are observed, scout the base of plants for eggs. Insecticides may be used when moths are active or when larvae begin to hatch. However, it is also possible to remove the eggs and destroy them prior to hatch. Alternatively, an early and late planting of squash can be used to ensure that some plants will not be affected by the squash vine borers.
If you observe an infested plant, remove it from your garden immediately and destroy it. Since cucurbits have multiple vines, you may be able to excise the damaged part of the plant and still retain fruit production. This will reduce the likelihood of the larvae successfully pupating and increasing the population for subsequent years. Spring and/or fall tillage of the garden will reduce the successful overwintering of the squash vine borer and result in reduced populations during the following year.