Squash Vine Borer: The Hidden Pest

With most insect pests of vegetables, UK Extension Entomology recommends weekly scouting to determine the levels of infestation and to decide if an insecticide is warranted. Scouting will tell when the earliest stages arrive and at what levels. However, this does not work well for squash vine borer because scouting for the single eggs laid on stems is difficult, and once evidence of infestation is apparent, it is too late to treat. Vegetables at risk to squash vine borer include some pumpkins, zucchini, summer squash, and some hard squashes.

Description and Life Cycle

Squash vine borer is a moth belonging to the clearwing group of moths, which also includes peach tree borer, dogwood borer, and grape root borer. While squash vine borer is a clearwing moth, it does not have clear wings. It is a paper wasp mimic, and it flies during the day imitating the activity of these common wasps. Eggs that are laid hatch in about 7 days. and the larvae immediately bore into plant stems. The first sign of attack is either frass pushed out through holes in the vine or wilting down of stems. Wilting vines can be confused with bacterial wilt of cucurbits, but the frass near the base where the wilting starts can be used to identify the squash vine borer.

Figure 1. Squash vine borer is a day-flying moth that resembles a common paper wasp (Photo: Ric Bessin, UK).

Figure 2. Fresh frass pushed out of the stem is a sign of squash vine borer activity (Photo: Ric Bessin, UK).

Some home gardeners and small-scale producers have used deworming as a method to reduce squash vine borer. This involves making a small slit parallel to the vine near the frass that has been pushed out by the borer and removing the borer. Generally, this practice is not recommended as it can cause more damage than the borer by opening up the vine to secondary infections.

Another home-garden practice used with long-vining cucurbits, like pumpkin, is to bury the vine in a few places where leaf petioles are attached. Just a shovel full of soil is needed. This often produces secondary rooting at these spots, which will help to support the vine if there is damage closer to the crown of the plant.

Management

Squash vine borer emergence as moths begins mid-June and continues through the end of July. Upon emergence, the moths mate and females lay their eggs. The eggs take about a week to hatch.  Yellow bucket traps baited with squash vine borer pheromone are effective to monitor for the start of moth activity. Insecticide sprays can then be applied 7 to 10 days after first moth activity and repeated every 2 weeks through the end of July.

Figure 3. Squash vine borer has one generation, but emerges over a long period over the summer (Photo: Ric Bessin, UK).

Figure 4. It is common to find squash vine borer moths resting on leaves of cucurbits or weeds during at midday (Photo: Ric Bessin, UK).

How you spray is just as important as when you spray for squash vine borer. The vines on the ground need to be protected, so high pressure is used to penetrate the canopy of leaves. Sprays need to be applied before eggs hatch as the target is the young larva before it tunnels into the vine.  In terms of selecting an effective insecticide, pyrethroids (IRAC group 3A), acetamiprid (group 4A), and some diamides (Group 28) are effective. Always read and follow pesticide label directions.

 

By Ric Bessin, Entomology Extension Specialist

 

 

Posted in Vegetables