University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Cucumber Beetles
a Major Vegetable Pest

May 28, 1998

Growing cucumbers or melons in your garden? The cucumber beetle is an annual insect pest to be concerned about. This small insect can cause considerable damage.

There are two reasons cucumber beetles spell trouble for certain vegetable plants. The first way is by direct consumption of leaves—a visible condition that is especially a problem when plants are small. Even more damaging, however, is the fact cucumber beetles can carry bacterial wilt disease, a serious problem of cucumber, muskmelon, and watermelon. Infected plants suddenly wilt and die after the beetles have been feeding.

There are two types of cucumber beetles, the spotted and the striped. Both are small beetles, less than 1/4-inch long and yellow-green in color. The striped cucumber beetle is most common in our area, and has three black stripes down its back. (The spotted has 12 black spots). Flip it over and the rear portion of the underside should be black. If it's yellow, it's the western corn rootworm beetle, not considered a serious pest of cucumbers or melons.

Cucumber beetles start feeding early in the season, often eating plant leaves emerging from the soil. If the beetle is carrying bacterial wilt disease, the plant becomes infected. Symptoms may not show until later into the season, when the vines wilt and die.

As plantings are made in the garden, watch for the cucumber beetle. Control it by applying either carbaryl (Sevin) or rotenone. Reapply at about weekly intervals if beetles are still present.

Once the plants start to bloom, apply late in the day and keep the insecticide off the blooms to avoid contact with bees and other pollinating insects.

Another early season control option is to use a polyester row cover. Put the cover over cucumbers and melons, making sure to seal the edges into the soil. Look carefully around the plants before doing this, however, to assure there are not any cucumber beetles present that could be trapped under the cover! Once the plants start to bloom, the cover needs to be removed so pollinating insects can get to the flowers.


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