sealPurdue News

July 1, 2002

Japanese beetles eating away at Hoosier trees, flowers and crops

WEST LAFAYETTE, Ind. – Japanese beetles are out in full force, munching away at trees, flowers and crops across southern Indiana. And in two more weeks, they will invade the rest of the state.

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These metallic green and bronze beetles are emerging for yet another summer feast on roses, shrubs, flowering fruit trees and deciduous trees such as linden, sassafras, sycamore, Norway, maple, birch and elm.

"Every year these beetles are drawn like magnets to the same trees and bushes in homeowners' yards and gardens," said Tim Gibb, Purdue University Extension entomologist. "If beetles are a nuisance now, they will be a problem for many years to come."

Japanese beetles feed on more than 300 different plant varieties, and newly transplanted trees are highly susceptible to damage, Gibb said. Adult beetles also may feed on corn and soybeans, causing serious damage.

Japanese beetles are here to stay for most of the summer – for 6-8 weeks depending on weather conditions. Since beetles emerged earlier in southern Indiana, they may remain longer. The sooner temperatures cool down in August and September, the faster beetles will dissipate.

For small plants, such as roses, vegetables and bushes, Gibb said Japanese beetles can be picked off on a daily basis and dropped into a milk jug of soapy water. Foliar insecticide sprays, such as newer pyrethroids, Malathion or Sevin, can be applied to larger plants and trees.

"Insecticides are only marginally effective in high populations because adults must consume insecticide-laden leaves to be killed, and the feeding on the leaves is what we want to prevent," Gibb said. "Adult beetles will fly up to five miles to find suitable plants, so treating beetles as they emerge from lawns does not prevent plant defoliation."

Sevin provides seven days of control, while pyrethroids, sold under a variety of trade names, may work for more than two weeks to ward off beetles, Gibb said. These materials should contain one of the following active ingredients: permethrin, esfenvalerate, cyfluthrin or bifenthrin. All insecticides should only be applied according to label directions, he said.

Gibb also said homeowners should consider replacing trees that attract this hard-to-kill annual pest with types that are resistant to the beetles' damage. A list of these resistant landscape plants and trees can be found in the Purdue Extension Japanese beetle publication E-75 on the Web.

Japanese beetles mate while feeding on flowers and leaves. During July, females lay eggs in turfgrass that hatch into white grubs in early August. Gibb expects to see a healthy population of white grubs this year.

July is a good time to apply preventative insecticides, such as Merit or Mach 2, to control grubs. Both products are long-lasting, but for best results the area should be irrigated after the insecticide is applied. If irrigation is not possible, timing the application before a significant rainfall also is beneficial.

"Seventy percent of grub control preventatives are put down needlessly," Gibb said. "Homeowners and gardeners need to apply these insecticides where they have had problems in the past or where soil sampling reveals five or more grubs per square foot of turfgrass."

The wet spring and early summer temperatures will have little affect on grub damage this year. Damage is mainly influenced by weather in July, August and September. If the summer remains wet, turfgrass will be able to tolerate more grub feeding and direct insect damage will be minimal, Gibb said.

Writer: Jennifer Doup, (765) 494-6682,

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

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

Related Web sites:
Japanese Beetles Emerging in the Rain

Purdue University Extension entomologist Tim Gibb expects to see a heavy infestation of Japanese beetles in Indiana this summer. The beetles feed on more than 300 different plant varieties, making them difficult to control. (Agricultural Communication Service photo by Tom Campbell)

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Purdue News Service: (765) 494-2096;

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