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Corn+Soybean Digest

Corn Rootworms and Japanese Beetles Debut in Cornfields

Corn rootworms and Japanese beetles are making an appearance in Illinois, says University of Illinois Extension Entomologist Mike Gray.

Despite saturated soils, corn rootworm injury is already showing up in fields across east-central Illinois.

“Unlike the previous two growing seasons, I believe this year’s rootworm population had a very good chance to establish on root systems and survive because of the early and quick pace of planting this spring,” Gray says.

On June 10, Joe Spencer, an entomologist with the Illinois Natural History Survey, confirmed this prediction when he observed severe corn rootworm larval injury on plants in his plots located just north of Urbana. Several nodes of roots had been pruned on many of the plants he examined.

Gray expects more injury is likely to occur in these plots because many of the larvae were still second instars and they will have a chance to continue chewing on additional root tissue as third instars.

Root systems may be shallower this year because of the saturated soils. Shallow root systems and severe root pruning could lead to significant lodging of plants in some fields. In some instances, even without corn rootworm feeding, shallow-rooted plants that become top heavy later this year could be susceptible to lodging.

“If lodging occurs, examine the plants’ root systems to determine the severity of root injury (if any),” Gray says. “Don’t automatically assume corn rootworms are responsible.”

Another familiar insect pest, Japanese beetles, were observed on corn plants and several flowering shrubs in Massac County on June 7.

Although sightings of Japanese beetles have been less common in central Illinois, they will become more numerous over the next week to 10 days, Gray predicts.

“If the rains stop long enough for field visits to begin again, don’t be surprised to see densities of this insect pest increase,” he adds. “I believe survivorship through the winter should have been good for the grubs and the early planting and root establishment will enhance the prospects for moderate to high populations of Japanese adults this summer.”

When scouting for adults in corn or soybean fields, move beyond the border rows. Research conducted in 2009 by Andy Morehouse, a graduate student in the department of crop sciences, indicates there are considerable differences in adult densities between the interior of fields and border rows.

For more information, check out The Bulletin, an online publication written by U of I Extension specialists in crop science.

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