If your squash and pumpkin plants are wilting despite frequent watering or you’ve spotted holes bored into the base of your cucurbit plant stems, you may have a squash vine borer problem. These colorful moths target squash, zucchini, pumpkins, and gourds, and they can devastate entire crops before you know you have a pest problem. Here is how to tell if squash vine borers are plaguing your plants, plus organic pest control tips to help you get rid of squash vine borers and keep them from coming back.
What Are Squash Vine Borers?
Found throughout North America, squash vine borers (Melittia cucurbitae) are a type of clearwing moth with a uniquely colorful look. Adults measure about half-inch long, and they have bright orange and black bodies and dark metallic green wings that buzz loudly as they fly. While borers don’t sting, they are “wasp mimics” that use their bold coloration to evade predators like birds, which often mistake them for wasps or bees.
Borers overwinter as cocoons in the soil and emerge as adult moths from late June to mid-July when they mate and lay eggs around the base of cucurbit plant stems. After about a week, those flat, brown borer eggs hatch into larval borers that measure about 1 inch long and look like maggots with white or cream-colored bodies and dark brown heads.
After emerging, larvae drill into the plant stems and spend the next four to six weeks chewing away at the interior of the stems and inside plant crowns. Then they dig their way out of their host plants and burrow into the soil, where their lifecycle repeats.
Gardens in cool climates may experience a single generation of borers per year. However, gardeners with longer growing seasons may need to contend with two generations of borers. Acting quickly at the first signs of borers is essential to avoid ongoing issues with these pesky insects.
Dean Schoeppner
Signs of Squash Vine Borers
If you head out into your garden in the early morning or early evening, you may be able to spot borer moths fluttering between the rows of vegetables in a distinct, zigzag pattern. However, squash vine borers are some of the sneakiest pests around, and it’s difficult to detect borer problems after the larvae burrow into the plants. The following signs and symptoms can alert you to the presence of squash borers even if you don’t see the moths in action.
- Wilting leaves and plant collapse. When borers tunnel into plants, they block water and nutrient flow and eventually cause plants to collapse and die. However, before this occurs, infested plants may look wilted in the morning and perk back up in the afternoon.
- Holes in plant stems. If your cucurbit plants have started to wilt, closely inspect the base of the plant stems for borer holes. Borer holes typically measure about ⅛ to ¼ inch in diameter, and they’re a sure sign that borers are hiding inside the plant.
- Mushy or rotted stems. Plants can develop secondary infections when borers drill into their stems. This can result in mushy stems and stem collapse.
- Piles of sawdust-like frass. Borer holes may be surrounded by piles of orange or green frass, as shown in the photo above. This is another clear indication of borers.
Storebought pheromone traps can serve as early warning systems to detect squash vine borers. You can also make a simple DIY borer trap by filling a yellow bowl or dish with water and a squirt of dish soap. Squash vine borers are attracted to the color yellow, but they can’t escape the trap once they fly in.
Preventing Squash Vine Borers
It’s challenging to get rid of squash vine borers once they invade, but there are ways to keep borers off your plants and out of your garden. Use the following tips to help prevent borer problems before they start.
Choose Resistant Plants
Squash vine borers are particularly attracted to zucchini, acorn, summer, and Hubbard squash, but they aren’t as interested in cushaw and butternut squash, melons, and cucumbers. If you’ve had issues with borers in the past, growing resistant cucurbits may help.
Use Crop Rotation
Rotating crops on a three- to five-year cycle can deter soil-dwelling pests, including squash vine borers. If you’ve had a major borer infestation, you may want to avoid growing certain types of cucurbits for a few years.
Install Row Covers
Crop rotation is even more effective if you use it in conjunction with floating row covers installed early in the season. Anchor row cover edges with landscape staples or heavy rocks to keep borers from creeping in, and remove the covers when borers are done laying their eggs to ensure your plants are pollinated.
Companion Planting
Companion planting with flowering herbs can attract predatory insects that prey on borer larvae. Radishes may help to deter squash vine borers, too. However, you can also protect cucurbits by growing a few sacrificial Hubbard squash plants as trap crops to draw borers away from more valuable produce.
Practice Good Sanitation
Squash vine borers overwinter in the soil and in old plant debris, but you may be able to interrupt their life cycle by destroying old cucurbit plants at the end of the season. Because pests can survive the composting process, it’s a good idea to burn infested plants or bag them and throw them in the trash.
Time Your Plantings
You can avoid most vine borer problems by starting cucurbits indoors in early spring and harvesting plants before borers emerge in mid-summer. If your growing season is long enough, you may even be able to grow a second crop of cucurbits in mid- to late summer, after borers have laid their eggs.
Protect Vulnerable Plants
Some gardeners deter borers by loosely wrapping the base of cucurbit stems with aluminum foil or old nylon stockings. Other gardeners prevent borers by spraying cucurbit stems with BT thuricide, which is approved for organic gardens but is only effective if it’s on the plant when borer larvae hatch and begin to burrow in.
How to Get Rid of Squash Vine Borers
You don’t need to use chemical pesticides to get rid of squash vine borers, but it’s important to act fast if you suspect that borers are affecting your plants. If you catch borers early, you can limit their spread and increase the likelihood that your plants will recover.
Handpicking
If you head out into your garden in the early morning, you may be able to handpick slumbering borer moths off your plants and into a bucket of soapy water. While you’re at it, check your plants for borer eggs and crush any eggs you find with your fingers or wipe them away with a paper towel drenched in soapy water.
Cut Borers Out
Cucurbit plants that are heavily infested with borers should be destroyed as soon as possible. However, you may be able to salvage plants with minor infestations by cutting borers out of the plant stems with a sharp, sterilized knife. Draw the blade along the plant stem, pierce any larvae you see inside, and then mound soil over the stem cut to help the stem heal and develop secondary roots.
BT Thuricide
While BT thuricide can be used as a preventative spray, you can also inject BT thuricide directly into plant stems with a disposable syringe to kill borer larvae inside the plant. Remember, BT thuricide needs to come into direct contact with borer larvae to be effective, and it doesn’t work against adult moths.
Tilling
Tilling infested gardens in fall or spring can interrupt the borer life cycle by bringing hidden borer cocoons up to the soil surface. Once the cocoons are exposed, predators like birds may gobble them up, but you can also recruit the help of your chickens if you have a backyard coop.
