Squash Vine Borer
Squash vine borers tunnel into pumpkins and squash vines.
Squash vine borer larvae are thick-bodied and will grow to be about 1" and have a whitish body and brown head.
The adult moths are 5/8- to 1-inch long and colorful. Their abdomens are usually orange with black dots. Their hind legs are orange and black and hairy. Their front wings are greenish-black, while the hind wings are colorless with dark veins.
Damage Caused by Squash Vine Borers
Squash vine borer (Melittia cucurbitae) tunnels in the vines of pumpkins and summer and winter squash; it rarely is found in cucumbers or melons and cannot complete its development except in squash or pumpkins.
Larva bore into the stems of plants leaving a trail of waste behind where it feeds on the stem tissues. While the larvae are most commonly found near the base of the plant, they can be found throughout the plant and even in fruit, particularly later in the season.
As the caterpillars feed, they will tunnel through the stems. This damages the stem tissues, and the plants cannot facilitate the movement of water and nutrients and will often cause wilting of vines, especially during the heat of the day. As feeding continues, the vines the caterpillars are feeding on may eventually die. The infestation is more serious during the extended dry period in early summer.
Life Cycle of the Squash Vine Borer
The adults fly during the day, often darting around in a zig-zag pattern.
- Because they fly during the day, they are commonly misidentified as wasps.
- The adults will emerge from mid-June to early July and lay eggs, primarily near the base of stems, but they can be found on other parts of the plant (elsewhere on stems and petioles).
- After the eggs are laid, they will start to hatch in about 10 to 14 days.
After feeding for 4-6 weeks, larvae will emerge and burrow into the ground, where they will eventually pupate. They will overwinter in the soil as pupae. In southern Illinois, there can be two generations.
Squash that still vine can be kept alive by rooting the stem every foot or so along the vine.
Management of the Squash Vine Borer
Susceptibility varies greatly among varieties. Zucchini, blue hubbard, acorn, and delicata are very susceptible. Butternut squash is highly resistant to attack.
- Covering plants with floating row covers can help keep squash vine borers off of plants.
- If you have had trouble in the past, make sure you are growing in a different area since they overwinter in the soil.
- Covers will need to be removed, or plants will need to be hand-pollinated once plants begin producing female flowers.
- Altering your planting date or planting a second crop in early July to avoid peak egg-laying can help reduce the likelihood that plants will be attacked.
- If you are growing vining cucurbits, bury a few nodes on each vine. This will cause the plants to root and can lessen the impact of any squash vine borers that may attack the plant.
- When vines begin to run, scout twice weekly for the moths and for the entrance holes and frass. If you notice any frass, you can cut the vine lengthwise near the entry hole and remove the larva.
- Once the larva is removed, cover the stem with soil.
If you decide to apply pesticides, apply them to the plants' crowns and runners when they begin to run. Apply late in the day to avoid pollinators. Once caterpillars are inside of the plants, foliar pesticide applications won't have any effect on them.
Contact your county Extension office for current pesticide controls.