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News Release
Rockford Extension Center
John Church, Extension Educator, Natural Resources
Ph. 815-397-7714
7/1/2016
Japanese Beetles on Landscape Plants
In Northern Illinois
Only a few years ago, Japanese beetles were something talked about as a potential problem in the
future. Now, they are present in northern Illinois in field crops and on landscape plants.
"Japanese beetles are one of the exotic insects that have made their way into the United States
and wreak havoc due to the lack of a natural predator," says David Robson, University of Illinois
Extension horticulture educator." And unlike most insects, both the adult and larval stages can
cause major injury."
Adult Japanese beetles are between 1/4 and 1/2 inch long. They're easily identified because of
their metallic green body with coppery wings. On either side of the wings are five tufts of white
hairs.
The larval stage is one of the three major grubs that feed on turfgrass, though not yet in the
numbers as the annual white grub from the June beetle or masked chafer. Beetles mate in June,
and the female lays eggs in early July. Eggs hatch out in August, and grubs continue to feed and
grow until they pupate in April or May. Most Japanese beetles start emerging from the ground in
late May. There is only one generation per year, but the adult stage can be present until early fall.
Adult Japanese beetles are voracious feeders, especially on sunny days, and seemingly
indiscriminate. Like most insects, they have their favorite food but will feed on anything present.
It was initially thought that beetles would feed for only a month or so, following a similar life
cycle as June bugs. However, reports indicate Japanese beetles feeding into September, though
numbers were drastically reduced.
"Roses, grape vines and linden trees seem to be the favorites in Illinois," says Robson. "The
Japanese beetles do not discriminate–all types of roses and lindens are fair game, even the
supposedly insect- and disease-proof shrub roses. You can find the insects on viburnums,
climbing hydrangeas, Shasta daisies, daylilies, porcelain vine and some fruit trees." Generally,
the beetle feeds on the tender upper leaf tissue between the veins, creating a skeletonized look to
the leaf. In many cases, what's left turns brown, giving the plants a scorched appearance.
Robson says large holes can be munched out of flowers, and occasionally you will find damage
to fruits and vegetables, though vegetables tend to be one of the last things the beetles will eat.
Most summer Illinois fruits, such as apples, peaches and pears, have a skin that is harder for
beetles to digest.
Control is difficult. Beetles may fly miles from where they emerge. Complicating matters is the
fact that in early July the creatures will take flight when disturbed; as they mature, they become
easier to pick off or knock off the plants.
United States Department of Agriculture • Local Extension Councils Cooperating
University of Illinois Extension provides equal opportunities in programs and employment
Page 2 of 2
News Release
Rockford Extension Center
John Church, Extension Educator, Natural Resources
Ph. 815-397-7714
7/1/2016
Adults can be controlled by knocking into containers of hot, soapy water. These efforts will
probably need to be repeated daily for several weeks. Start as soon as possible.
Netting can be used to cover some prized plants, but make sure there are no beetles under the net
when you apply it.
Japanese beetle traps have shown effectiveness, though reports indicate that they actually attract
more beetles into the yard that may not be caught by the traps. The current recommendation is to
not use traps at all, or to place them at least a city block or more from your yard.
There are several insecticides that can be used as knockdown sprays. The insecticide carbaryl,
often sold as Sevin, provides some of the best control. More than likely, you will have to repeat
applications every five to seven days. Other products include acephate (Orthene) and cyfluthrin
(Tempo). Imidacloprid (Merit) is often sold as Japanese beetle control, but it is a systemic, which
means it must be applied early in the season, usually early May, to allow the plant to absorb it.
Be sure to read and follow directions, locating "Japanese Beetle" control on the label.
Grubs can be controlled with imidacloprid (Merit) or Milky Spore disease, a bacterial toxin that
will only have an effect on the Japanese beetle grub.
Above all, maintain the health of the plant. Plants damaged during the summer are more likely to
suffer from reduced leaf surface that reduces sugar production. Plants may grow less and have a
more difficult time recovering from stress conditions such as drought, early frosts, diseases and
other insect attacks.
Plants will often recover and appear fine next year, living on stored food reserves. But, repeated
defoliation in early summer will weaken many trees, shrubs and vines.
Keep plants watered and properly fertilized. Contact your local U of I Extension office for more
information on maintaining plant health. Or visit http://www.extension.uiuc.edu/.
-30Source: John Church, University of Illinois Extension Educator, Natural Resources, Rockford
Ph. 815-397-7714
United States Department of Agriculture • Local Extension Councils Cooperating
University of Illinois Extension provides equal opportunities in programs and employment