A summer vegetable garden is just not complete without summer squash growing in the mix of tomatoes, peppers, okra, and cucumber. However, harvest time may prove disappointing for some squash and cucumber growers.
There are insects that have a special affinity for all members of the cucurbit family, including squash, cucumbers, melons, and pumpkins.
This week, there have been many questions about squash plants that have seemingly died overnight. Many of these plants have fallen victim to the squash vine borer. The vine borer is an insect that can destroy the squash plant quickly and with very little warning.
The squash vine borer overwinter as a larva or pupa enclosed in cocoons in the soil where squash has been previously planted.
The adult emerges as a moth in early summer and lay eggs on the stems of the plants. The adult moths are half-an-inch across at the wings and black in color. They are day fliers and are often mistaken for wasps. After a week, the pale grubs hatch and eat their way into the stems near the soil level.
As it feeds, larvae tunneling up the stems of the squash plant causing damage and restricting flow of water. Both of these actions cause the plant to wilt. Symptoms of squash vine borers are a sudden wilting of a vine and sawdust-like insect waste coming from holes in the stem called “frass”.
The squash vine borer is difficult to control because the problem is not identified until after severe damage has been done to the plant.
For example, it’s difficult to know if they are present until the plant starts to wilt and damage has already begun. Unfortunately, once they are inside the stem of the squash not much can be done.
Various measures can be taken to control this pest. Tilling the soil in late winter can expose overwintering insects. Also, rotating squash placement in the garden can decrease the vine borer population in different areas of the garden. Plant as early as the weather allows because borers do not emerge until early spring.
Once the garden is planted, yellow sticky traps or yellow bowls of soapy water can be placed in the garden to attract the adult borers.
They will be more inclined to go to the traps than the yellow flowers of the squash. Some Organic growers plant radish around their squash to repel the adults.
If there appears to be borer activity in the garden such as bits of “frass” along the base of the plants, then cut a vertical slit along the vine and remove the larvae.
Removing borers or killing them with a long pin or needle can reduce their numbers. When the vine is split, mound soil around the base of the squash plant at the stem.
With good growing conditions, the plant should put down more roots ahead of the borer damage, and the infested part of the plant can be removed.
Insecticides will control squash vine borers, but they should be used late in the day to prevent harm to bees.
Bifenthrin, sevin, esfenvalerate, and permethrin are effective on these insects, but each has a waiting period before the fruit can be harvested.
The best advice is to stay ahead of the borer. Planting squash as early as possible is the best option for a good harvest.