The squash vine borer is a clearwing moth that is found east of the Rocky Mountains, from Canada to South America. The adult borer resembles a wasp, with an orange abdomen with black dots. They have two pairs of wings, the first being a metallic green, and the hard-to-see underwing being clear. The larvae stage of the Squash Vine Borer resembles a white or cream-colored worm with a brown head.
This worm grows to about one twenty-fifth of an inch long. These brightly colored adults lay their copper-colored eggs on the vines of certain plants. Once these eggs hatch, they burrow into the vine off the plant, cutting off the nutrients and leading to the collapse of the infested plant.
Squash vine borers typically affect squash, zucchini, pumpkins, and other gourds. The squash vine borer is not usually interested in butternut squash, melons, and cucumbers, but any plant that has a vine can fall prey to this small worm.
How to Spot a Squash Vine Borer Infestation
The first sign of a squash vine borer infestation is that the infected plant will go limp and wilt, even in the most perfect conditions. If the root of the plantis still firmly in the ground, root-damaging pests such as voles can be ruled out.
The next step is to check the for holes near the base of the plant. Small holes surrounded by a sawdust-like material (the squash vine borer’s frass, or droppings) is all that is needed to identify the presence of this pest. The squash vine borer eats the inside of the stem of plants, which will cause plants to rot at the site of the entry.
Unfortunately, once the plants have reached the point of wilting, they have usually been too severely damaged by this invasive worm to be saved. A last-ditch effort a gardener can take is to try and extract them. This involves carefully cutting the plant in an attempt to find the bugs, but it is typically easier (and less time-consuming) to try and prevent an infestation.
How to Prevent a Squash Vine Borer Infestation
Once the larvae have breached the vine of the plant, it takes substantial time and energy to rid the plants of the pest. The best way to prevent a squash vine borer problem is to try and stop it before it starts.
Insecticides do work on these bugs as a last-ditch effort, but their use must be perfectly timed and applied as the eggs are hatching. Once the larvae are inside the vine, insecticides will not work. Diatomaceous earth or black pepper sprinkled around the stalks of the plants, when they are small, and reapplying after rain, has also shown to be effective in deterring the squash vine borer.
Despite the fact that the adult moth of the squash vine borer can help pollinate a garden, the population boom from the eggs they lay offsets the benefit the adult moths bring. Preventing the destruction of a plant mostly involves preventing those adults from laying their eggs to begin with.
Cover newly planted seeds and transplants with netting that will not allow the adults to access the plants. Once the plants have matured, showing at least two or three sets of leaves, remove the netting and cover the base of the plant, the most vulnerable part, with a four-inch-long strip of aluminum foil. The strip of foil should extend beyond the base of the plant by a quarter of an inch. Florist tape can also be used if you don’t like the look of the aluminum foil in your garden. If the plant outgrows the strip of aluminum or florists tape, unwrap it, and rewrap the base of the plant with a longer strip. This treatment not only protects the base of the plant from the larvae, it stops the adults from laying their eggs.
Trapping the adults is also an easy way to prevent destruction of squash plants. This plan of attack is best carried out at twilight or in the early morning, when the moths are resting on the upper leaves of the plants. The adult squash vine borer moths are also attracted to the color yellow, so they can be caught using yellow sticky pads or yellow-colored bowls of soapy water.
Focusing on growing vine plants that don’t typically fall prey to squash vine borers is an easy way to avoid having to deal with an infestation. These plants include butternut squash, cucumbers, melons, or watermelons. If tailoring your squash variety is not a viable solution, a second planting of summer squash planted in early July will mature after squash vine borers have finished laying their eggs—or simply planting an extra amount of squash will help offset the any amount lost to these bugs. The life cycle of the squash vine borer is only six to eight weeks, and they can only eat so much.
How to Manage a Squash Vine Borer Infestation
Once the plant has started to wilt, it is unlikely that it can be saved, but there are a few last-resort attempts to try and save it. The least invasive technique is to try inserting a wire into the stem that has been breached to try and kill the larvae inside.
If this does not work, carefully cut the infected part of the stem, where the entrance hole of the larvae is seen—lengthwise, not across the plant. Be careful not to cut the plant any farther than necessary, but make sure to remove any squash vine borers you can see. Once all observed squash vine borers have been removed, cover the split part of the vine with moist soil.
If none of these techniques are effective in saving an infested plant (or more than one), immediately remove any affected before the squash vine borers infect healthy specimens. Destroying the vines, either after removal or after harvest, can help keep squash vine borers that are still in the larval stage from developing further.
If you’re a gardener who has had a plant fall to the squash vine borer, you know how hard it can be to get rid of the pests once they have already entered the stem. Time and energy is better spent trying to avoid an infestation, whether by trapping the adult borers or by protecting the plant, then by trying to remove the larvae after they have hatched and entered the stem. These pests can affect the amount of harvest an infected plant yields, so if you are setting your hopes on a limited amount of vine plants, be even more vigilant to make sure to catch squash vine borers before they become a problem.
Want to learn more about how to fight squash vine borers?
The Old Farmer’s Almanac covers Squash Vine Borer
Extension.org covers Biology and Management of Squash Vine Borer in Organic Farming Systems
Bonnie Plants covers Surgery for Squash Vine Borers
Penn State University studies Squash Vine Borer
University of Kentucky outlines Squash Vine Borer and Squash Bug
University of Minnesota Extension covers Squash vine borer management in home gardens
Grow Journey covers Prevent and Stop Squash Vine Borers
Savvy Gardening covers Prevent Squash Vine Borers Organically
Abbie Carrier graduated from Texas Woman’s University with a Bachelor’s of Science in history and a minor in political science, and she is currently working on a Master’s of Arts in arts administration from the University of New Orleans. With this degree, she hopes to gain a position in museum curation, and she currently works as a grant writer for nonprofit organizations. She enjoys writing about the arts, history, politics, and topics related to science, health, lifestyle, and entertainment.