sealPurdue News

July 9, 1999

Japanese beetle population rises

WEST LAFAYETTE, Ind. -- Armies of Japanese beetles invaded Hoosier lands last weekend, and more are sure to come.

Purdue University entomologist Tim Gibb said the beetles emerged about two weeks ahead of schedule and are expected to peak in about a week at 10 times the normal numbers.

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"The beetles have already completely defoliated some of the linden trees on Purdue's campus," said Purdue entomologist Cliff Sadof.

The dry spring weather this year contributed to the large brood of beetles. "Wet and humid weather is perfect for a fatal fungal disease that grows on the beetles," Gibb said. He said that when spring is dry -- as it was this year -- the fungus isn't as abundant, and the beetle population flourishes.

Also, this spring's weather was near perfect for growth of favorite beetle foods: the leaves and flowers of crabapple trees, fruit trees, rose bushes and grapes.

"The fact that adult beetles are out sooner this year also means that the eggs will be laid in turfgrass and will hatch into white grubs sooner this year," Gibb said.

Japanese beetle grubs can overwinter in lawns to emerge as beetles next summer. They can cause serious injury to lawns by feeding on the root systems.

To control grubs in lawns, homeowners can use the insecticides Sevin, Diazinon and Dylox. According to Gibb, these are "rescue" treatments, which means that the chemicals work if applied after the grubs have hatched -- usually the end of July or early August.

For long-lasting grub control, Gibb suggests using Merit, GrubX or Mach 2. If these products are applied in July, they will still be active in August when the grubs appear.

"At this point, there is nothing you can really do as far as preventive measures for adult beetles except spraying plants with pesticides," Gibb said. "But it's not too late to prevent grubs, which may help to reduce the numbers of beetles next year."

To avoid future problems, Sadof suggests planting trees or shrubs that are resistant to beetle attacks. For example, 18 varieties of crabapples are highly resistant to Japanese beetles. These include Candied Apple, Prairifire and Brandywine.

"Japanese beetles are always going to be with us, so one way nursery growers, landscapers and homeowners can turn this debacle into an opportunity is to keep a list of the badly damaged plants," Sadof said. "If you're in a place where there are lots of Japanese beetles, write down names of plants that were badly hit this year. Pretty soon you'll have a list of plants you should avoid."

Sadof said that despite taking precautionary measures, people still may find ruined lawns and defoliated trees. "Heavy infestations might still defoliate trees, because the pesticide takes time to be ingested and take effect," he said. "By the time the pesticide has killed the beetles, an entire tree may already be eaten."

Well-established, healthy landscape plants should survive even total defoliation by Japanese beetles, but younger plants could be killed by heavy damage. The adult beetles sometimes feed on corn and soybean crops, as well.

The Japanese beetles are expected to gorge themselves on Hoosier plants well into September, according to Gibb. "I expect them to peak for about three weeks, then slowly die out in mid-September; so they will be with us for about three months."

More information on Japanese beetles is available in the Purdue Cooperative Extension Service publication E-75, "Japanese Beetles." Additional information about beetle-resistant trees and shrubs is available in the Purdue Extension publication ID-217, "Crabapples Resistant to Apple Scab and Japanese Beetle in Indiana." Both publications are available online as Adobe PDF documents. Copies also are available for a fee from the Extension office in each Indiana county or from the Purdue Media Distribution Center, (888) 398-4636.

Sources: Tim Gibb, (765) 494-4570;

Cliff Sadof, (765) 494-5983;

Writer: Naomi J. Haley, (765) 494-8396,

Purdue News Service: (765) 494-2096;


Jim Scott, course superintendent at Purdue's Birck Boilermaker Golf Complex, displays a linden tree that was defoliated by Japanese beetles, which are on the loose in Indiana. (Agricultural Communication Service Photo by Tom Campbell)

Color photo, electronic transmission, and Web and ftp download available. Photo ID: Gibb.beetles

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