Japanese Beetles are here!

Staff Writer
Aledo Times Record

Japanese Beetles have been spotted in Western Illinois at the University of Illinois research farm in Monmouth, IL. "It is too early to tell how bad the Japanese beetle problem will be this year," says Martha Smith, extension educator in horticulture with University of Illinois Extension.

Japanese beetles are present in high numbers for about 6 weeks. They feed on the foliage and flowers of a wide range of plants, being most common on smartweed, crabapple, linden, birch, willow, rose, grape, apple, peach, and brambles. They do not feed heavily on needled evergreens, ashes, magnolias, oaks, and maples other than Japanese maple. They feed during the day at the top of the plant on the leaf's upper side--they appear to like sunshine. Individuals typically fly to another food plant every 3 days. These flights tend to be long, from 3/4 to 1-1/2 miles.

Heavy feeding results in holes in the leaves and can progress on favored hosts to skeletonization, with only the major leaf veins remaining. As apples, peaches, plums, berries, and other fruit ripen, the beetles attack them, completely covering the fruit. Apples are eaten to the core, whereas the skin of peaches is commonly left uneaten,leaving a dry, empty shell where fruit once was.

Control of the adult beetle is difficult and challenging since they move frequently. Generally pesticide sprays, such as Sevin and products containing acetamiprid, bifenthrin or cyfluthrin, can reduce damage for two to several days, but several applications are required to maintain control. Read and follow all label directions. An alternative option is handpicking when they first arrive in your garden.

“Research has shown that beetles are attracted to previously attacked plants,” Smith explains. “Home gardeners can greatly reduce damage by handpicking, particularly for the first week or two after beetle emergence. If you keep feeding damage to a minimum when they first arrive, it is likely you will have less damage overall.” Use a widemouthed jar (such as a peanut butter jar) containing rubbing alcohol or a detergent and water mixture. Hold the jar under a beetle, poke it, and the beetle will fold its legs and fall into the jar, being killed by the alcohol or drowning in the soapy water. Doing this daily or every other day for the first couple of week’s results in plants with little damage compared to the neighbors' plants. Throughout the rest of the season, beetles will be more attracted to heavily damaged plants elsewhere in the neighborhood. Prized roses and ripening fruit can be protected by covering with floating row covers.

Beetles mate, and the females tunnel into the turf to lay eggs. These eggs hatch into white grubs that feed on the turf's roots, resulting in browning and dieback of the turf in late summer and fall. Female beetles are strongly attracted to moist, actively growing turf, so stopping or reducing irrigation during July results in reduced egg-laying, with fewer grubs. The beetles go to the neighbors' moister, greener lawns to lay their eggs. Typically, unwatered lawns do not have enough white grubs to warrant insecticide application.

Grubs feed in early to mid-May, and again in late summer. If during these times you have brown areas of turf that can be pulled up in large sections like a carpet, suspect grub damage. If you see at least 12 grubs per square foot, a lawn grub treatment is recommended in early August. Right now the adults have emerged and a lawn treatment would be useless – the grubs aren’t


Dr. Phil Nixon, Extension Entomologist, University of Illinois emphasizes an important point, "Just because you control grubs in your lawn does not mean you will reduce the population of the adult beetles in your yard this summer." "The beetles can fly for several miles, so there will be just as many on your plants whether you treat for grubs or not."

To date, imidacloprid (Merit, Bayer Advanced tree and shrub insect control, and other brand names), and other systemic insecticides are labeled to control adult beetles in certain plants. However, recent research has found that since these products last a long time in the plant and kill all insects, they are a serious threat to our pollinator populations. "These highly systemic insecticides have been increasingly shown to move into the flower pollen of various plants where they are picked up by pollinating insects including honey bees and bumble bees." "Until we know more about translocation into pollen in various plants, it is prudent to avoid these insecticides in applications to plants attractive to pollinators,” explains Dr. Nixon.

Prepared by: Martha A. Smith, Horticulture Educator, University of Illinois Extension, serving

Henry/Mercer/Rock Island/Stark Counties, #309-756-9978,