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] |