Phone calls and e-mails are already coming to me about the dreaded squash vine borer. This insect bores into squash stems, causing them to wilt during the day. Pretty soon, they eat so much of the stem that the squash dies. Unfortunately, they also bore into zucchini plants.
The adult that is responsible for the destruction is a wasp-shaped moth that emerges in the spring and summer in our area. The moths are about 1 inch long, clear-winged with orange and black abdomens, coppery green forewings and clear hindwings.
The females light briefly and repeatedly on the squash plants, depositing a single, pinhead-sized, reddish brown oval egg each time. Preferred egg-laying sites are stems, especially near plant bases, but the moths can glue eggs onto all parts of a squash plant. Each female deposits about 200 eggs during its one-month life span.
Brown-headed, white, wrinkled larvae hatch in about a week and immediately bore into the stem, leaving behind a souvenir of yellow or tan grainy excrement on the stem exterior. The larvae feed for about four weeks, continually pushing excrement out their entry holes. After this they emerge to burrow about
2 inches in the ground, where they pupate.
I don’t know of anything completely foolproof for preventing vine borers. Several people have completely quit trying to grow squash. I will share what other UGA county agents and professionals have recommended, along with other things that have been passed along to me.
Once the borer has gotten in a vine, people have tried to mound the dirt over the stem at a spot on the vine ahead of the larvae. With the right amount of water and temperature, theoretically, the squash will re-root, and the infested part of the plant can be severed and removed. This can buy you some time, but sometimes the larvae eat faster that what you can cover, plus the plant is already too compromised or stressed to survive the heat.
Others have used row covers. With good contact with the ground, row covers can give a squash plant a significant head start over the vine borers. Row covers are lightweight commercial garden fabrics that drape over frames or the plants themselves. After the first female flowers appear, the row covers should be removed to allow for pollination. The vine borers might still affect the crop, but by that time you should be able to harvest a lot of squash.
Gardeners can make a vertical slit in the stem with a sharp knife and manually removed the larvae. One plant can have several. Afterward, soil should be mounded over the stem to encourage rooting. This can be time-consuming.
Yellow sticky traps and yellow bowls of soapy water can be used to trap or drown the adult moths, which are attracted by the yellow squash blossom.
Some gardeners even inject the insecticide Bt, or Bacillus thuringiensis, into the squash stems. But contact insecticides are generally not effective, as the larvae are protected inside the plant.
Spraying the stems with insecticides doesn’t seem to work that well, at least not in the long run. Spraying several times a week with carbaryl (Sevin), esfenvalerate or bifenthrin can help, but about the best you can hope for is buying a little more time.
An organic vegetable producer told me years ago that she plants radishes around her squash and it keeps the vine borers out. I have passed this along to several people over the years. About an equal number of people tell me it works as doesn’t work.
Every day, after the adult moths lay eggs on the plants, you could pick them off. But this is extremely time-consuming. I tried this several years ago when I had two plants each of zucchini and squash, and it took me 30 minutes each day to pick off all the eggs. I think I gave up after about a week.
One thing that helps somewhat is to plant your squash as early as possible so that the plants are already strong and healthy before the vine bores are active. Be prepared to cover your plants should we have a late spring frost.
Others have tried planting alternative squash varieties such as snake gourd or Cucuzza, which are resistant to the vine borer.
To discourage this pest, till your soil in the fall and again in the spring to kill over-wintering pupae and rotate squash family plants (zucchini, etc.) to a different location the next year.
REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.