COLUMBIA, Mo. – Farmers, gardeners and homeowners should keep their eyes peeled for shiny, green and bronze Japanese beetles feeding on the crops, vegetables and flowers.
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This insect’s wide variety of food preferences make scouting a necessity.
“Certainly we need to be looking at this point,” said Wayne Bailey, a state entomologist for University of Missouri Extension. “These beetles are gregarious feeders, so if you have one, a lot will come in because they tell others through chemical signals that the food is good in an area. You might have a few in your garden the first year, the next year it might be in the hundreds and then the year after it could be in the thousands.”
Dry weather this year has affected the emergence of mature beetles. While some areas saw Japanese beetles first emerge as early as May, many are seeing populations peak in the last weeks of June.
“Japanese beetles first emerged about three weeks early this year because the warm winter allowed the white grub to emerge earlier,” Bailey said. “In a normal year we’d be having numbers similar to last year, but with this drought we’re not sure if numbers will be similar, higher or lower, but some of our traps are catching substantial numbers.”
The dime-sized green beetle – with bronze wings and white tufts of hair around its shell – feeds on any plant that has a pleasant smell.
“They do eat about 440 different plants, but their favorites include Linden trees and roses,” Bailey said. “They feed high in the plant, out in the sunlight, and can do a lot of damage to trees and ornamentals and shrubs.”
Japanese beetles also can feed on soybean leaves and corn silks, especially in the critical pollination period.
“In corn the economic threshold is three or more insects per ear when pollination is less than 50 percent complete and silks are chewed to less than a half inch from the ear husk, but sometimes you will get 20-30 or more beetles feeding on one ear,” Bailey said. “In soybean the threshold is set at 20 percent defoliation this year because of higher soybean prices.”
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 1932 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. In July, the adults lay eggs, which hatch and develop into white larvae that overwinter in the soil and mature during the spring. They emerge as beetles around 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 Japanese beetles, or just pick the beetles off the plant.
“One of the things we discourage is putting out pheromone traps because they will bring in more beetles to your area than what would normally be there, and that can build your numbers faster,” Bailey said. “These beetles typically can move about three miles per year, and it’s very common in an area where you don’t have very many to see numbers climb exponentially from year to year.”
Find current insect numbers in your region from the University of Missouri at http://ipm.missouri.edu/pestmonitoring/jb/.
Read more about Japanese beetles and find pesticide recommendations at http://ipm.missouri.edu/IPCM/2012/6/Japanese-Beetle-Adults-Emerge-Across-Missouri.