These beetles 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, or a few
weeks later this year due to the later start. The life cycle is
similar to a June bug, only 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.
One reason for potentially low beetle numbers is the
extremely dry soil conditions we had last year. Of course, all
bets are off if you watered your lawn and the neighbors didn't.
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 these 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 travel 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
future.
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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 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.
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 small fruits,
garden produce, shrubs and small trees near main building entrances
and other important landscape locations where damage is obvious.
Protecting a newly transplanted linden tree is a good idea. Covering
plants with floating row covers can protect ripening fruit and
prized roses.
[By
JOHN FULTON,
University of Illinois Extension] |