Garden Variety: Japanese beetle making itself at home
The number of Japanese beetles in the Lawrence area and much of northeast Kansas is bigger than ever this year. The beetles have been in the area for a few decades but mostly in isolated populations or low enough numbers that seeing one was a somewhat rare occurrence. This year, the population has finally grown enough and the weather has been just right for the Japanese beetle to really live up to its bad reputation.
Japanese beetle adults are close in size and shape to what most people know as May and June beetles. They are smaller than May and June beetles, though, and shiny green to coppery brown in color. They also have distinctive white tufts at the edges of their wings. Another native cousin, the green June beetle, is also shiny green, but lacks the copper tone and white tufts. The green June beetle is also larger, clumsy and much less destructive than the small but voracious Japanese beetle.
Damage from Japanese beetle adults is often described as skeletonizing because the beetles chew holes in leaf tissue between veins, leaving what looks like a leaf skeleton. They chew from the top of the leaf or feed on flowers and pollen when present. Japanese beetle adults love roses; linden trees; apple, crabapple, peach, cherry and other fruit/flowering trees; crape myrtle; Japanese maple; and soybeans. They will feed on many other plant species as well.
Adult Japanese beetles live from 30 to 45 days. They are done emerging for the year but may seem to continue to grow in numbers in gardens where their favorite plants are present. This is because the beetles send out chemical signals called pheromones to attract additional beetles once they find an ideal food supply. Adults can fly up to five miles.
Adults take short breaks from chewing up the landscape to mate and lay eggs in the soil. The eggs will hatch later this summer into white grubs that feed on roots — preferably of grass. Japanese beetle larvae are considered a major pest of lawns, athletic fields, golf courses, and sod farms. They look very similar to other common white grubs (larvae of common May and June beetles).
To control Japanese beetles, use a combination of management strategies. For small populations, hand-pick beetles or flick them into a jar containing rubbing alcohol or soapy water. Remove grassy weeds or other weeds that are attractive to adult beetles such as smartweed. Keep plants healthy by watering, mulching, etc. as needed to maintain good plant health.
After removing feeding adults, cover choice plants with bird-netting or other fine mesh netting and secure it so beetles cannot enter. Remove the netting at the end of the summer when beetles have passed.
Japanese beetle traps are not recommended on small properties as they may attract more beetles than they catch. On large properties, traps can be placed away from plants the beetles are attracted to and may capture up to 75 percent of the beetles. Traps use a pheromone and a bag, bucket, or other container to capture adults.
Contact insecticides are an option for heavy populations of Japanese beetle adults that are causing substantial damage to plants. There are many products labeled for use on Japanese beetle adults. Applications will have to be repeated because additional beetles will fly into the area and find the same desirable plants.
All of the insecticides available for Japanese beetle adults are also lethal to honey bees, other native bee species, and to many predatory insects. If applications must be made, apply insecticides in early morning or late evening when bees are least active. Try using netting to exclude beetles or hand-picking as a follow-up to avoid multiple applications.
Systemic insecticides are generally not effective on Japanese beetle adults.
Japanese beetle was first reported in the U.S. in New Jersey in 1916 and is believed to have been transported to the U.S. from Japan on nursery stock. The insect has slowly moved westward, and Kansas is still only partially infested.
The USDA Animal and Plant Health Inspection Service estimates that farmers and ornamental plant growers spend more than $450 million annually to control Japanese beetle or replace plants destroyed by it.