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Northern corn rootworms in home gardens

Jeffrey Hahn

Northern corn rootworm on rose

Photo credit: Jeff Hahn

Northern corn rootworm on rose.

A northern corn rootworm, Diabrotica barberi, is a small insect, about 3/16th inch long. It is a pale, uniform green, lacking any type of markings (e.g. spots or stripes). It is common in Minnesota and throughout the Midwest wherever corn is grown. This summer, northern corn rootworms have been particularly numerous probably due to favorable weather conditions.

This beetle typically has a one year life cycle, although there is evidence that it can be extended to two years. Northern corn rootworms overwinter as eggs. These eggs are laid in the soil at the base of corn plants. They hatch the following June and the larvae start to feed on corn roots. The larvae are active for four to six weeks before pupating. They emerge as adults in July, about five to ten days after they pupate. After feeding they lay eggs, generally during August and September.

Adults typically feed on the silk of corn plants. However, they can also feed on the blossoms of a variety of flowers and can have an impact in nearby gardens. They chew ragged holes and can make blossoms unsightly. The severity can range from slight to heavy.

If you encounter a problem with northern corn rootworms, you have several options. You can ignore them especially if they are not very abundant. You could also physically remove them by shaking plants so the beetles fall into a pail of soapy of water. If they are numerous and you wish to preserve your flowers, you can easily manage them with an application of a garden insecticide, such as permethrin, esfenvalerate, or carbaryl.

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