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3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

5/7/01

Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101, drlewis@iastate.edu
Elaine Edwards, Continuing Education and Communication Services, (515) 294-5168, eedwards@iastate.edu

Yard and Garden Column for the Week Beginning May 11

Borers Bug Squash Plants

By Donald Lewis
Extension Entomologist
Iowa State University Extension

Did you plant squash or pumpkins in your garden last year? If so, you probably remember the pain and anguish of watching your blue ribbon-winning plants wilt in the heat of summer or turn crispy black right before your eyes. What happened?

Two unrelated insect pests, the squash bug and the squash vine borer, are common pests that should be familiar to home gardeners. If you have not seen these insects, keep planting squash and you will. Both are more obvious in the second half of the summer but now is the time to be planning for their next appearance in your garden.

Squash Bug
The squash bug is distributed throughout the United States and attacks all cucurbits and vine crops but is most damaging to squashes and pumpkins. The disagreeable odor noticed when they are crushed gives rise to the nickname "stink bug."

Squash bug adults are 1-inch in length, gray-brown, elongate oval and pointed at the head end. After hibernating in plant debris or other protected locations the bugs fly to vines as they start to run and lay clusters of a dozen of more, large, brick red eggs on the lower sides of the leaves.

The nymphs are green when they first emerge from the eggs but soon turn gray as they grow. They generally remain in clusters as they feed on sap from the leaves. They grow for 4 to 6 weeks and reach maturity and transform into adults by the end of the summer.

Heavy squash bug infestations cause a rapid wilting of the plant. Heavily injured leaves become characteristically blackened and crisp as they die. Small plants may be killed early in the growing season. Larger plants may have isolated damage on certain leaves or runners.

Squash Vine Borer
The squash vine borer is unrelated to the squash bug. All they have in common is exploitation of the same group of plants. Squash vine borer is a pudgy, white caterpillar that tunnels inside squash plant stems (usually near the soil line) from June through August. Symptoms of infestation are a sudden wilting of the vines or the accumulation of moist, white sawdust around the base of the plant.

The squash vine borer is a moth that resembles a wasp. In early summer they fly during the day to visit plants and lay their eggs on the outside of the stems. Tiny caterpillars tunnel into the plants and remain inside for the rest of the summer. At about the time harvest is complete the borers leave the stems and burrow into the soil to spend the winter.

Management Options
Protecting squash and pumpkin vines from these insect pests is difficult. Both pests must be prevented rather than cured. If the insects are grown and the damage is already severe there is little that can be done to save the plants.

One option is to tolerate the damage (also known as the "take-your-lumps" philosophy of garden pest management). Squash bug and vine borer damage may be severe, but infested plants are often able to live and produce in spite of insect activity. Yield may not be as great or quality might not be as high, but you saved the time, expense and possible adverse side effects of using insecticides in your garden. The risk inherent in this approach is that damage might be so severe that you lose the entire crop. If that happens, there are always squash and pumpkins at the local farmer's market to replace your crop losses.

Handpicking squash bugs, egg masses and young nymphs from the plants are viable control alternatives for some. Similarly, borers can sometimes be successfully extracted from infested stems with a sharp knife. Other gardening activities that may help reduce future infestations include removing and destroying infested vines as soon as harvest is complete and thorough tilling of the garden soil.

If the potential losses from these pests are intolerable then limited and careful use of insecticides early in the season might be your preferred strategy. To prevent squash vine borer damage treat the base of the plants with a residual insecticide at the time the moths are flying (early to mid-June). Sevin and rotenone insecticides are commonly used for this purpose. Sprays provide a much better barrier against borer attack than do dusts.

Watch for squash bug nymphs and spray infested plants as soon as they appear. Use garden insecticides such as Sevin, permethrin or insecticidal soap according to label directions. Sprays are again more effective than dusts, and treatment of small nymphs is much more effective than later sprays against large nymphs. Avoid spraying plants in bloom. If spraying during bloom is necessary, spray at night after honey bees have quit foraging for the day.

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ml: isugarden


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