Beware of Cucumber Beetles

URBANA -- Striped cucumber beetles (Acalymma vittatum) and spotted cucumber beetles (Diabrotica undecimpunctata howardi) have been attacking vegetable gardens since the beginning of spring, and they continue to feast on the leaves, blossoms, and fruits of many crops, said Kelly Allsup, University of Illinois extension educator.

Cucumbers, beans, melons, and squash are their preferred foods. They also transmit bacterial wilt and mosaic disease, which can kill plants.

“It takes about 6 weeks for a plant to collapse, so if you have had perfectly healthy squash plants die rapidly, this could be your culprit,” Allsup explained. “To determine if the plant has the disease, cut a leaf in half. If there is a sticky sap that oozes from the cut, it has a bacterial disease, which causes blockage in the water-conducting tissues.”

Adult striped cucumber beetles overwinter in wooded areas and garden debris in Illinois and migrate from the southern states in the early spring. As they feed, they lay their eggs in the soil at the base of the plants. The larvae hatch in 2 to 4 weeks and feed on the plant’s root systems. The larval stage is followed by a pupating stage, which also occurs in the soil.

Cucumber beetles can be devastating to some crops. U of I Extension suggests using row covers when the plants are young. As blossoms form, remove the row cover to allow pollination.

Spinosad- and pyrethrum-based chemicals can be used to control adults. However, it is important to spray at night to avoid damaging beneficial insects and pollinators. For example, soldier beetles (Chauliognathus sp.) prey on cucumber beetles.

Cleaning up weeds and debris that could be used for overwintering and crop rotation can help to prevent infestation. Use mulch to deter the beetles from laying eggs.