SPRINGFIELD, Ill. — Thanks in large part to a mild winter, the pesky Japanese beetle is having one of its more prolific years.

 

“It’s been a really good year for insects, overall,” said Kelly Estes, an entomologist and state survey coordinator for the Illinois Cooperative Agricultural Pest survey program at the University of Illinois.

Growers first dealt with black cutworms in the spring, are dealing now with Japanese beetles and corn earworms – and could see an increase in brown marmorated stink bugs next early next month, Estes said.

Whether to break out insecticides, and how much to use, to combat the hard-shelled beetles first depends on determining how dense they are within fields. It’s quite possible that any applications may be limited to field edges because the bugs often tend to congregate in large groups.

“So, you want to make sure you scout throughout the field. Just field-edge treatments are often a possibility with these defoliators, particularly if you’re looking at soybeans,” Estes said.

The beetles’ favorite food tends to be rose bushes and leaves on linden trees, said University of Missouri entomologist Ben Puttler, but in large clusters the bugs can do some significant damage to corn and soybean plants, if left alone.

Beetle numbers are reported higher in a number of regions in the Midwest, particularly in Missouri, Iowa and western Illinois. Other parts of Illinois, such as southern Illinois and its numerous orchards, have not been as affected.

“We’re not seeing too many beetles this year,” said Wayne “Ren” Sirles of Rendleman Orchards. “I mean, they’re around, but we’re not having to worry too much about them.”

Other than a mild winter helping to boost the beetles’ numbers overall, scientists don’t have a handle as to other reasons for the bugs’ increase.

“We’ve seen with the Japanese beetles that there has been an increase this year,” explained arborist Chris Johnson in Davenport, Iowa. “It’s kind of a cyclical insect, where the populations go up and down every so many years.

“It’s a bug that basically feeds on the cambial tissue of the leaves, thus taking out the chlorophyll, which is the food factory for the tree.”

Estes advised that corn and soybean growers first determine the extent of any beetle infestation in fields overall before turning to insecticides.

“With corn starting to tassel and getting close to tassel, it’s important to remember even though densities may appear to be extremely high, the average density of beetles across the field may be below levels of economic concern,” she noted.

Treatment for corn plants should be considered during silking if there are three or more beetles per ear of corn; silks have been clipped to less than a half-inch; and pollination is less than 50 percent complete, Estes said.

For soybean growers, treatment should be considered during a limited window, she said. “Insecticidal treatments should be considered when defoliation reaches 30 percent before bloom and 20 percent between bloom and pod fill.”

For smaller areas such as home gardens, common over-the-counter products that contain carbaryl, such as Sevin, are effective deterrents. Common bug traps also work well, Puttler said.