Japanese beetle adults are
one-half to three-fourths inch long with copper-colored wing covers
and a shiny metallic green head. A key characteristic is prominent
white tufts of hair along their sides.
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 attacked.
Adults can be with us until
mid-August. The life cycle is similar to a June bug. After mating,
females lay eggs in turf. 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 commonly recommended to
control Japanese beetle grubs. In our area milky spore is generally
not recommended since it controls only Japanese beetle grubs and not
our predominant lawn grub, annual white grub. Also, Japanese beetle
grubs must already be infesting the turf for milky spore to work
effectively. Pesticides commonly used for lawn grub control, such as
diazinon and Grub-X, will also control Japanese beetle grubs.
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Controlling Japanese beetle
grubs does not significantly reduce the number of adult beetles the
following year. The beetles are good fliers and easily travel a
couple 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. Sevin
is toxic to bees. Synthetic pyrethroids can also be effective. The
Japanese beetle repellent made from Neem has not been shown to be
effective. 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. And, of course, protect
your prized roses and other items you might want to exhibit at the
Logan County Extension office]