sealPurdue News

July 24, 1998

Japanese beetles arrive early in Indiana this year

WEST LAFAYETTE, Ind. -- Japanese beetles, the bane of the summer gardener, have appeared in Indiana weeks sooner than usual, which will allow them to spend more time munching their way through Hoosier gardens, says Purdue entomologist Tim Gibb.

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"They may be a huge pest this summer," Gibb said. "They came out early this year, 10 days to two weeks earlier than normal." According to Gibb, the large numbers and early arrival of Japanese beetles this summer are due to the mild winter and the good growing conditions for plants this summer.

Gibb said that insecticide treatment for Japanese beetles -- which usually involves applying insecticides to lawns to kill insects in their immature, or grub, stage -- should begin as soon as possible. "Anyone using insecticide brands such as Mach 2 or Merit treatments can go anytime up until the first week in August," he said. "These materials only work against grubs early in their development." The grubs eat the roots of grass until they mature and fly away to nibble on hundreds of other plants.

Gibb said other chemicals can be used as "rescue" treatments to prevent lawn damage by the grubs. Insecticides such as Sevin, Diazinon, Oftanol or Dylox, can be used during the first two weeks of August if they are followed by plenty of irrigation.

The early arrival of the beetles means that they will have more time to munch away on our summer gardens. "Just because they came out early doesn't mean they'll end early," Gibb said. "They'll probably last until the first frost, but the peak adult activity will occur around the end of July."

Japanese beetles feed on more than 300 different species of plants, but they are especially fond of roses, grapes, flowers, and overripe or decaying fruit. "Adult Japanese beetles feed on fruits, vegetables, crops, ornamental plants -- anything green," Gibb said.

Chemical insecticides, such as carbaryl (Sevin) or malathion, can be used on these plants to ward off the beetles. "You should understand that these chemicals won't last a long time. Retreatment will probably be necessary," Gibb said.

Another popular form of Japanese beetle control is with pheromone traps. These traps use scents to attract the beetles, which then are caught in the trap. The traps do work at one level -- they are very good at attracting beetles -- but that is exactly the problem. They are known for attracting more beetles to an area than would be there naturally. A common joke among entomologists is that for a trap to work in your yard, you should give one as a gift to your next-door neighbor. "Whatever you do, don't put traps near plants that are susceptible to beetles," Gibb said.

Although Japanese beetles are best known as a pest in homeowners' lawns and gardens, in periods of heavy infestations they can attack agronomic crops too, including corn and soybeans. "We just had our first reports of Japanese beetles feeding on corn silk in the southern part of the state," Gibb said. "The crop planting was so variable this spring that this will expand the opportunity for beetles to feed in the corn fields this year. They'll just move from one field to another as the crop matures."

Gibb said that insecticides may be needed in certain circumstances:

  • On corn, if the beetles have cut the corn silks back to less than 1/2 inch before the corn is 50 percent pollinated.
  • On soybeans, if the defoliation is greater than 40 percent before blooming, greater than 15 percent in the period between blooming and pod fill, or more than 25 percent from pod fill to harvest.

Gibb said that although the beetles are off to an early start this year, that is no indication of what the population will look like in Indiana next summer. "I've learned not to bet on Japanese beetles," he said. "One thing that controls their population is microbial diseases that occur in the springtime. Whether we have a large population the summer before, or whether there is a cold or warm winter doesn't really matter that much. It's more whether the conditions are right for the disease to spread in the springtime."

For more information about Japanese beetles, the Purdue Cooperative Extension Service offers two publications that are available at county Extension offices or via the Internet as Adobe PDF documents:

For general information, ask for Extension publication E-75, "Japanese Beetles," available on the Internet.

For additional information about controlling Japanese beetles in soybeans, ask for Extension publication E-77, "Soybean Insect Control Recommendations," available on the Internet.

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

Writer: Steve Tally, (765) 494-9809;;

Purdue News Service: (765) 494-2096; e-mail,

CAPTION: Japanese beetles are one-half inch long and are metallic green and brown. Because of the mild winter, the familiar pests arrived early in Indiana this summer. (Purdue Entomology Department illustration.)

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