The Japanese beetle has reached its peak population in places across Iowa. While some areas of the state have not seen the beetle’s appearance at all, isolated spots have seen early spurts of incredibly high numbers. Professor and Iowa State University Extension Entomologist Donald Lewis says that typically it’s toward the end of June that Japanese beetles emerge over a 3-4 week period. This year though, it seems they have all appeared at once.
Lewis says that highest on their list for invasion in the linden tree. Japanese beetles also are also attracted to all forms of fruit trees, as well as ornamentals plants like rose bushes. Between 300-400 different kinds of plants are listed as hosts for the Japanese beetle adult, ensuring for a wide variety of places they could appear.
There are no easy solutions for dealing with or preventing damage to trees and plants. Some options Lewis recommends for treatment are less harmful to the environment but often take a lot of time and effort for success.
“’Surround’ is a clay material that you mix with water. When it dries it’s a deterrent for beetle feeding. Another botanical insecticide is ‘Neem’ which is another feeding deterrent. It doesn’t kill any beetles, it just makes them go somewhere else to feed, at least for a few days, but then you’re going to have to reapply.”
He also recommends screening plants with a fine netting to create a barrier, handpicking the beetles if the plant is small enough, and spraying your plants early and often. Lewis finally says that although it’s an unpopular remedy, he recommends simply living with the damage because despite frequent belief, a defoliated tree isn’t actually dead.
On this Hort Day discussion of Talk of Iowa, host Charity Nebbe speaks with Lewis and Iowa State University Extension Horticulturist Richard Jauron. They discuss Japanese beetles and answer gardening questions from listeners.