seal  Purdue News

July 21, 2003

Japanese beetle damage to reach peak in late July

WEST LAFAYETTE, Ind. – Japanese beetles will reach their peak activity in Hoosier gardens at the end of this month due to cool spring days and a late summer start in the Midwest, said Purdue University entomologist Tim Gibb.

"Their populations typically peak during mid-July, however, this year the greatest number of beetles will arrive during the end of July because of cool temperatures during late spring," Gibb said. "Also, with recent rain and water accumulation, the beetles have not been quite as active as usual."

Japanese beetles are most active during hot, dry weather. And with a population estimated to be higher than average, the beetles will soon be at their destructive peak, zeroing in on Indiana trees, flowers, fruits, gardens and some crops.

In areas of heavy infestation, adult beetles will attack and injure flowers and foliage, and the grubs, or immature larvae, may seriously damage lawns, turf grass and cultivated crops by feeding on the roots.

"They love to munch on anything green," Gibb said.

Japanese beetles feed on more than 300 different species of plants, but they are especially fond of linden trees, flowering crab apple trees, roses and grapes. Gibb said that well-established, healthy plants should survive even total defoliation by Japanese beetles, but younger or weaker plants could be killed by heavy damage. To ward off the adult beetles, apply a chemical insecticide, such as carbaryl (Sevin) or malathion, to trees and shrubs on a regular basis.

Traps, which use scents to attract and catch Japanese beetles, are often purchased in an effort to control the insects.

"Japanese beetle traps are effective at trapping many beetles, but unfortunately the net result is that more beetles end up in yards where traps have been set up, and more feeding damage results," Gibb said.

To control the damage to lawns by Japanese beetles, Gibb recommends applying an insecticide treatment to kill the insects in their immature, or grub, stage.

"As a preventative method, we suggest applying an insecticide such as Mach II or Merit in July," he said. "These materials only work against grubs early in their development."

The beetle larvae develop in lawns, turf and cultivated land from eggs laid by the female in mid-summer. Gibb said they pass the winter in the grub stage, complete their growth the following spring and emerge as beetles beginning in mid-June.

"At this point the beetles are here to stay. We just need to learn to live with them and deal with them in the best possible manner," Gibb said.

To reduce Japanese beetle damage, Gibb suggests planting trees that are resistant to beetle attacks. For example, four varieties of oak trees – white oak, scarlet oak, red oak and black oak – are resistant to Japanese beetles.

More information on Japanese beetles is in the Purdue Cooperative Extension Service publication E-75, "Japanese Beetles in the Urban Landscape," available online. Additional information concerning insect control in turf grass is available in the Purdue Extension publication I-61, "Turf grass Insect Management."

Writer: Meggie Issler, (765) 494-8402,

Source: Tim Gibb, (765) 494-4570,

Ag Communications: (765) 494-2722; Beth Forbes,;

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