Written by: Charlotte Glen, Horticulture Agent

Have you ever ventured into the garden in early summer and found your squash or zucchini plants have collapsed, seemingly overnight? If so, you know firsthand how destructive squash vine borer can be to all types of squash, zucchini, and pumpkins. These deadly pests are actively laying eggs on squash plants in our area. Once the eggs hatch and the borers enter squash stems little can be done to kill them, making now the time to act to protect your squash and zucchini plants from imminent destruction

Understanding Squash Vine Borer

Native to the eastern half of the US, squash vine borers are the most destructive pest of squash, zucchini, and pumpkins in our region, killing almost every plant they infest. While they look more like a wasp, the adult squash vine borer is actually a type of moth, though its wings lack the colorful scales that cover the wings of most moths and butterflies. Another un-moth like behavior of adult squash vine borers is that they fly around in the daytime, making them easily visible in the garden. At this time of the year they can be seen hovering around squash plants, laying their eggs on squash stems near the base of the plant.

In a few weeks these eggs will hatch and the borers, which are a type of caterpillar, will bore into squash stems, where they will feed for four to six weeks. It is this feeding activity that kills squash plants, causing them to quickly wilt and die. If you inspect the lower stems of plants infested with squash vine borers you will see holes in the stems, from which emerges a wet sawdust like material known as frass.

Controlling Vine Borers

Gardeners should inspect their squash and zucchini plants now for signs of borers. If holes and frass are already present, the only thing that can be done is to try to remove borers by hand. Borers, which look like a creamy white grub with a brown head, can be removed from stems by carefully slitting the stem open lengthways and removing them. This method is most effective when borers are small and only practical in small plantings.

Both organic and synthetic pesticides are available to control squash vine borer, but timing is the key to effectiveness. Once the borer enters the squash stem treating with insecticides is a waste of time. To protect plants, insecticides must be applied just before the eggs hatch; this will be occurring over the next four to five weeks in our area.

Whether using organic or synthetic insecticides to control this pest, make sure to apply them thoroughly along the stems of squash plants, especially near the base of plants. Spraying plant leaves will provide no protection. Among organic pesticides, those containing neem, spinosad, or pyrethrin as the active ingredient are the most effective for controlling vine borers. Because organic pesticides break down quickly, they will need to be reapplied every three to five days over the next four to five weeks to provide squash plants ongoing protection from this pest.

Synthetic pesticides that control vine borers include those containing permethrin, bifenthrin, or carbaryl (also known as Sevin), as the active ingredient. These products should be applied every seven to fourteen days (depending on label directions) over the next 4 to 6 weeks to provide squash plants ongoing protection. Since name brands change frequently, always check the active ingredient of any pesticide before purchasing it. You will find the active ingredient listed on the front of the label. Also be sure to check the label for the pre harvest interval. This is the amount of time you must wait after spraying a crop before you can pick it. Apply pesticides late in the afternoon to minimize damage to honeybees.

Other practices that can reduce squash borer populations include removing crop debris from the garden at the end of the season and destroying infested plants during the season. Avoid planting squash in the same location year after year since this pest lives through the winter in the soil. Since this pest is active while squash plants are flowering, covering plants with protective row cover is not a practical control measure, since that will also screen out bees and prevent crop pollination.

Learn More

Learn more about squash vine borer and other common pests of the squash family from this Clemson Extension fact sheet: http://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2207.html

This Kentucky Extension fact sheet includes great images of squash bugs and vine borer: http://www.ca.uky.edu/entomology/entfacts/ef314.asp

If you have gardening questions, contact your local Cooperative Extension Office. If you live in Pender County, call 259-1235. In New Hanover County, call 798-7660 and in Brunswick County call 253-2610, or visit https://www.ces.ncsu.edu/