They also have an overwhelming appetite for your favorite rose.
Adults feed in herds on many deciduous trees, shrubs and vines
such as linden, Japanese maple, sycamore, birch, elm and grape.
They generally do not feed on dogwood, forsythia, holly and
lilac. Japanese beetle adults feed on flowers and fruits and
skeletonize leaves by eating the leaf tissue between the veins.
Feeding is normally in the upper portions of trees. Beetles
prefer plants in direct sun, so heavily wooded areas are rarely
Adults can be with us until mid-August. The life
cycle is similar to a June bug, except that it runs a few weeks
later. After mating, females lay eggs in turf, and the eggs
hatch into grubs in August. Grubs feed on plant roots until cold
weather drives them deeper into the soil. Adults emerge in
summer of the following year.
The bacterial control, milky spore sold as Doom or Grub
Attack, is frequently recommended to control Japanese beetle
grubs. In our area milky spore is generally not recommended,
since it controls only Japanese beetle grubs. Also Japanese
beetle grubs must already be infesting the turf for milky spore
to work effectively. Pesticides commonly used for lawn grub
control will also control Japanese beetle grubs.
Controlling Japanese beetle grubs does not significantly
reduce the number of adult beetles the following year. The
beetles are good fliers and easily fly a couple of miles in a
single flight. Evidence suggests that adult beetles are
attracted to previously damaged leaves. Therefore reducing
feeding damage now can result in less feeding damage in the
Generally pesticide sprays of cabaryl sold as Sevin can
reduce damage for up to two weeks, but four to seven days is
more likely. Sevin is toxic to bees. Synthetic pyrethroids can
also be effective, but they tend to break down quickly with
extreme heat. These would include permethrin and bifenthrin. The
Japanese beetle repellent made from Neem has not been shown to
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Picking beetles off by hand every couple of days may be just as
effective as spraying. When disturbed, the beetles fold their legs
and drop to the ground. Covering plants with floating row covers can
protect prized roses and ripening fruit.
Japanese beetle traps are not recommended since they can actually
increase damage by attracting more than they kill.
A number of birds, such as grackles, cardinals and meadowlarks,
feed on adult beetles. Two native predator insects and a couple of
introduced parasites may help to keep Japanese beetle populations in
check. Protect natural enemies by keeping the use of conventional
pesticides to a minimum.
Although damage looks devastating, Japanese beetle feeding rarely
kills plants. Therefore, confine control of beetles to shrubs and
small trees near main building entrances and other important
landscape locations where damage is obvious. Protecting a prize
rosebush or a newly transplanted linden tree is a good idea.
Patches of yellow grass are appearing in lawns now. The symptom
is nitrogen deficiency, but adding nitrogen won't green those areas
back up. Really what is happening is that the abundant rainfall has
filled all the pore space in the soil, and this results in
"suffocation" of the grass. One of the first symptoms of lack of
oxygen is nutrient deficiency symptoms, such as the light-colored
grass. Location in the vicinity of tree roots makes things even
worse since the trees are more efficient scavengers of nutrients.
University of Illinois Extension, Logan County]