Question:
How do I prevent damage to my squash plants from the squash vine borer?Answer:
The squash vine borer is a common pest of squash and pumpkins in home gardens in Iowa. Damage first appears as wilting of the vines. Eventually, affected plants collapse and die.
The adult squash vine borer is a wasp-like moth. Adult borers emerge from the ground in late spring. Adult females lay eggs at the base of squash and pumpkin vines. Within a few days, the eggs hatch and the larvae bore into the stems to feed. Larvae feeding in the center of the stems block the flow of water to the rest of the vine, causing it to wilt. Severely affected plants wilt and die. The larvae feed inside the vines for several weeks, then exit the stems and burrow into the soil to pupate. They remain in the soil until late spring of the following year.
To manage these pests, several tactics can be used. Often, using several together provides the best control.
Row Covers
Row covers can be placed by early June to exclude adult vine borers from accessing the stems to lay eggs. Secure covers with bricks or soil to prevent adults from slipping underneath. The row covers must be removed when flowers open to allow for pollination. Squash requires insect pollinators to move pollen from male to female flowers, and row covers will exclude pollinators and squash vine borers. Additionally, row covers should not be used if squash was grown in that area the previous year, as the adults will emerge from the soil under the row cover.
Second Planting
In some situations, a second crop can be planted in late June or early July after the adults are finished laying eggs. This approach can work for squash that mature in less than 90 days, like zucchini and other summer squash, but will not be effective for pumpkins and many other winter squash that take longer to mature.
Crop Rotation
Crop rotation is also beneficial since these pests pupate in the soil nearby. While this can reduce the potential of pest infection, adults are highly mobile, so crop rotation is best used in conjunction with other approaches.
Disrupt Their Lifecycle
Fall tilling can disrupt and expose overwintering pupae, reducing the population that overwinters. Affected plants should be promptly removed and destroyed to prevent larvae in the stem from pupating in the soil and continuing the cycle in future years.
Use Insecticides
Preventing squash vine borer damage usually requires treating the base of squash and pumpkin vines with a residual insecticide when the moths are flying (early to mid-June in Iowa). Home gardeners can apply carbaryl (Sevin), permethrin (Eight), bifenthrin, spinosad, or other labeled garden insecticides. Sprays are generally more effective than dusts.
Trap Crops
Commercial growers will utilize a trap crop to manage squash vine borer. Blue Hubbard squash, which is highly attractive to the borer, is planted nearby, and most adults lay their eggs there, sparing the other, more desirable, vine crops. Once the blue Hubbard squash are infected, the plants can be removed and destroyed. An insecticide can also be applied to the trap crop to control the pest, reducing the need for pesticide use on the desirable crop, such as zucchini or pumpkins. However, this strategy requires more space than most home gardeners have to implement effectively, so it may not be a viable option for your garden.
Learn more in this article: Squash Vine Borer.