The Squash Vine Borer (SVB) is a red-orange and black winged insect. They emerge in early to mid-summer and lay their eggs at the base of squash stems. When those eggs hatch, larvae emerge and bore their way into the plant stem, continuing to eat your squash plants from the inside out until they are ready to pupate. Gardeners may not even notice their presence until they see squash plants wilting in the summer heat. Upon even closer inspection, a yellow, sawdust like appearance and entry hole at the base of the stem is often found. Once this is observed, it is often too late. While early June may feel too early to start scouting for these guys, it’s the perfect time to start planning defensive strategies to help protect your garden.
The first thing you can do, especially if you have a history with these insects, is select resistant cultivars. Knowing which types of squash are common targets can help you determine whether you will want to keep a closer eye on them this season, or maybe plant something different, altogether.
Cucurbita pepo is highly susceptible to Squash Vine Borer. This species includes Zucchini and summer squash. They have thin, hollow stems, which make it easy for these critters to get into. Pumpkins are also in this category. However, pumpkins are more likely to vine out and lay roots along the stems touching the soil surface. This helps the plant to withstand damage a bit better than its other counterparts.
Cucurbita maxima, which includes winter squash like giant pumpkins, Kabocha and Blue Hubbard varieties, is also susceptible to the SVB. While it is less preferred than C. pepo, it can still be targeted.
Cucurbita moschata is the most resistant plant species. C. moschata includes the butternut, honeynut and crookneck squashes. Their stems are thicker and more succulent, making them least favorable for the SVB to lay eggs on. Therefore, while not impossible, they stand a good chance against this garden pest. These insects are also rarely found in cucumbers and melons.
It is important to rotate your planting sites each year. These insects overwinter as pupae in the soil and emerge as adults in June-July. Planting in the same place each season is like placing a gift on their front doorstep. Moving your planting site and adding a protective row cover as soon as you plant can improve your odds at keeping the SVB away from your plants altogether. Leave the row cover until both male and female flowers begin to emerge. After that it is important to remove the row covers so pollinators can access the flowers.
For gardeners unable to rotate their gardens, preventative measures can still be taken. Do not use row covers as they can trap the pest in with your plants. Some recommend placing aluminum foil around the first couple inches of stem at the soil line to prevent insects from laying eggs and boring through stem tissue. Treating the base of the plants with a preventative pesticide may also be effective.
Chemical management is often tricky with these pests, and home gardeners may not feel it is worth the effort. Importantly, chemical management is no longer effective once the larvae have entered the stems, since they are then protected by the plants. In addition, these products can impact the pollinators visiting your cucurbits, so it’s important to carefully consider the full impact of chemical management. Always read the label in full and follow all instructions as prescribed.
Start scouting for the adults early. In mid to late June, check the base of stems for eggs and early boring damage. You may even see the adult insects flying around. Symptoms, like wilting, often begin in late June and become more common in July.
If you have a strong stomach and sense of adventure, you can carefully slice into the stem to try to find the larvae and extract it. Vining squash species may recover if the pest is removed and portions of vine are then buried in the soil, allowing new roots to take over and support the vine.
Alternatively, removing affected plants entirely and disposing of them in the trash may help to break the life cycle and remove pests from your garden for future seasons.
Since these insects typically only have one generation per year, your hard work does have a finish line. Paying extra attention and working to manage the SVB in early summer will allow your squash to grow healthy for the rest of the season. A second crop of summer squash can be planted in July, once adults are no longer out and laying eggs. This second crop should be unaffected by the SVB and produce healthy squash for your family to enjoy!
The UConn Home Garden Education Office supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension Center at extension.uconn.edu/locations.
