Japanese beetle damage and control
Fishburn, University of Illinois Extension
Send a link to a friend
[June 09, 2012]
Japanese beetle adults may be munching
on roses, lindens, raspberries, birch trees, crabapple and apple
trees in your neighborhood. The beetles are voracious foliage and
fruit feeders on nearly 300 species of plants. Feeding on plants
generally lasts for about six weeks.
The Japanese beetle is approximately a half-inch long and is
metallic green with coppery wing covers. The beetles chew the
leaf tissue between the veins, leaving a skeletonized leaf.
Adults most actively feed from 9 a.m. to 3 p.m. on warm, sunny
days. Normally they start feeding on the upper portions of
plants and work downward. Japanese beetles prefer plants exposed
to direct sunlight.
Since they are an introduced species, Japanese beetles donít
have any natural predators in the United States.
Damage to trees and shrubs is considered to be primarily
aesthetic. According to Phil Nixon, Extension entomologist,
"even heavily attacked trees and shrubs rarely exhibit severe
dieback, because the beetles attack after the bulk of food
production has already occurred in the leaves." "Photosynthetic
production primarily occurs early in the season when the leaves
are still soft and pliable. Japanese beetle defoliation occurs
later in the growing season," he explained. "This allows one to
selectively treat those trees and shrubs in very obvious
landscape locations and to ignore the damage on others."
There are several control options for Japanese beetles.
When the adult beetles change hosts, they prefer foliage
previously damaged by other Japanese beetles, so early
hand-removal of the beetles is effective. In the late afternoon
and evening, disturbed beetles fold their legs and drop to the
ground. By holding a container of rubbing alcohol (isopropyl
alcohol) or soapy water under beetles and poking at them, one
can easily collect a pint or so in less than an hour. If this is
done every day or two for the first couple of weeks after the
beetles emerge, subsequent damage through the summer is reduced.
Although labor-intensive, this is a viable option.
Netting is used to provide complete
protection. Rosarians protect prize individual buds and blooms
or even entire plants with netting. Backyard blueberry growers
use netting as well. Shade cloth with a high light
transmittance, spun-bound polyester row covers, netting sold in
fabric stores, window screening and other meshes all work well.
[to top of second column]
Insecticides provide effective control of adult Japanese beetles.
Heavily attacked plants can be sprayed with carbaryl (Sevin),
cyfluthrin and pyrethroid. Always read and follow label directions
for safe use of pesticides. Sevin is toxic to bees and other
beneficial insects and should be sprayed in the evening. Protect
natural enemies such as birds and predator insects by keeping the
use of conventional pesticides to a minimum. Spray only plants where
damage is very noticeable or food crops that are under attack.
Plants in less obvious parts of the landscape and large trees can go
Pheromone traps are available that contain an externally produced
hormonelike chemical attractive to male Japanese beetles and a
floral lure attractive to female beetles. The pheromone traps are
useful for detecting beetle emergence but are not recommended as a
control. Research shows that beetles are attracted from a
considerable distance to areas near the traps, but then switch their
seeking behavior to food plants, resulting in heavier plant damage
near traps. Even though the traps catch large numbers of beetles,
their use is not recommended.
[By JENNIFER FISHBURN, horticulture
University of Illinois Extension, Logan-Menard-Sangamon Unit]