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Insect Quiz June 2004

You are in your garden one fine June day taking a look at your squash plants. You are pleased because they are looking pretty good so far. But as you look more closely, you notice some small greyish insects with black legs clustered on a few of the leaves. As you closer, you also find a few larger brown insects that looks like it could be the same bug. You don't really notice any damage so far but these insects look suspicious.

1. What are these insects?

These insects are squash bugs (Anasa tristis). Adult bugs are grayish brown and 5/8 inch long. Nymphs are about 3/16 inch long with red heads and legs and green bodies when they first hatch. As they age, they eventually become greyish with black legs and 1/2 inch in length. Squash bugs feed primarily on squash and pumpkins, but they may also feed occasionally on other cucurbits. Both adults and nymphs are secretive and hide when disturbed. They are often found on the undersides of leaves.

2. Where did they come from?

Adult squash bugs overwinter in sheltered places, like under plant debris or rocks. In early June, adults begin to appear and females lay yellow to bronze colored eggs in clusters on the undersides of leaves. Squash bugs feed throughout the summer and there can be a second generation later in the summer. Squash bugs can be active into October.

3. Do they injure plants?

Squash bugs feed by sucking the sap out of leaves. This feeding can cause yellow spots which can eventually turn brown. In severe cases, wilting can result. Large plants are able to tolerate feeding, however young seedlings may die from extensive feeding. Squash bugs can also feed later in the season on the fruit.

4. What is the best way to treat these insects?

First keep plants healthy with adequate water and nutrients as they can better tolerate feeding. Since young plants are most susceptible to squash bug feeding, early season management is very important. Inspect plants for squash bugs beginning in early June. If only a few are seen, handpick and crush them or throw or knock them off into a bucket of soapy water. Crush eggs between your fingers.

Also avoid mulch as squash bugs use it as shelter to protect themselves during hot weather. You can set out boards or shingles in your garden. The squash bugs will use them for shelter overnight. You can then handpick and destroy them in the morning.

If you want to apply an insecticide, the best time to treat is early in the season, soon after eggs have hatched. Use an insecticide such as carbaryl (e.g. Sevin) or permethrin (e.g. Eight), or esfenvalerate (e.g. Ortho¨ Bug-B-Gone¨ MAX Lawn and Garden Insect Killer) to protect your plants. The best time to treat is early in the morning or late at night to avoid bees. Insecticides are less effective later in season when adults are present and populations are larger. It is not important to treat squash bugs found during fall.

If you have ongoing problems with squash bugs be sure to remove plant debris in the garden at the end of the season to eliminate overwintering places. Next season, consider planting varieties that are more resistant, such as Butternut squash, Royal Acorn squash, or Sweet Cheese squash.



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