Japanese beetle hits fields and lawns across the state of Missouri

If the leaves of your roses, shrubs or soybeans look like swiss cheese, the culprit could be Japanese beetles.

The population of the dime-sized insect continues to climb and will peak later in July. The green beetle with bronze wings and white tufts of hair around its shell is amid a multi-year population boom.

"They will build for the next five to seven years before some of the normal pathogens and predators move in to drop that population to a more balanced level," said Wayne Bailey, a University of Missouri Extension entomologist. "They are gregarious feeders and come to feed in groups of up to 25 beetles or even more."

In a three-day period, Bailey collected more than 1,600 Japanese beetles in a single pheromone trap in Columbia, Mo.

Japanese beetles show little discrimination in filling their stomachs, feeding on any plant that has a pleasant smell.

"Roses and linden trees are their favorite crops, but they'll feed on a wide variety of ornamentals, fruit trees, grapes and 440 different plant species," Bailey said. "They usually feed on the tops of plants in the sunlight, and they like plants that smell succulent, so if it smells good to you they likely will prefer those plants."

Field crops also appear on the menu for the Japanese beetle.

Both corn and soybeans can receive significant damage if control measures aren't implemented.

"For corn farmers it can be a serious pest because they target corn tassels and silks and chew on them," he said. "If the silks are taken down to less than half an inch in length, you won't get pollination, thus reducing corn production for that particular ear."

In soybean plants, Japanese beetles chew at the leaves instead. They prefer lush leaflets at the top of plants and can hurt yield by significantly defoliating the plant.

"If you get 25 percent damage to the leaves on soybeans. you can afford to treat your field to protect the rest of the crop," Bailey said. "In corn we recommend treatment if there are three or more beetles per ear that are producing green silks and pollination is less than 50 percent complete."

Japanese beetles arrived in the United States in the early 1900s, probably in potted irises from their native Japan. They were first found in New Jersey in 1916 and by mid-century had spread to Missouri, where they caused problems with ornamental plants and other crops. About 10 years ago MU entomologists began seeing Japanese beetles in more rural areas of the state and they are now found in most counties. The insect can fly up to three miles to find a tasty, fragrant meal.

Japanese beetles live for one year. The adult lays eggs in July that hatch and develop into white larvae, which overwinter in the soil and mature during the spring. They emerge as beetles in mid-June and begin feeding. Each healthy female lays 40 to 60 eggs. Adults live up to 60 days.

Homeowners can fall back on a staple insecticide, powdered Sevin (carbaryl), to combat the destruction of Japanese beetles.

"Sevin is probably one of the best, because it's readily available and relatively safe to most everything around," Bailey said.

More information on the insect and appropriate pesticides is available in the June 20 issue of the MU Plant Protection Program's Integrated Pest & Crop Management newsletter at http://ppp.missouri.edu/newsletters/ipcm/archives/fullissue/v21n12.pdf.