Japanese beetles and potato leafhoppers

By John Fulton

[June 30, 2008]  Everyone who thought we had escaped the Japanese beetle attack this year may have to rethink that. The beetles are running a week or two behind schedule, due to the cool spring. A few beetles have shown up in the area. Whether these are local hatches or tag-a-longs from southern areas doesn't much matter. They are coming.

Japanese beetle adults have a one-half- to three-fourths-inch-long body 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, 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.

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 and not our predominant lawn grub, the 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 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 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.

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 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. 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 rose bush or a newly transplanted linden tree is a good idea.

Potato leafhopper

In keeping with the insect theme, potato leafhopper numbers exploded last week. This is the small wedge-shaped, light green insect that seems to just fog around security and patio lights. They are not only a nuisance, but they can cause damage to a wide variety of plants.

Potatoes are the first plant that comes to mind when we talk about potato leafhoppers (must be something about the name), but many other plants ranging from beans to trees can be affected. You may be wondering what kind of damage a few little leafhoppers can do, especially since they suck sap from plants and aren't that big in size.

Leafhoppers suck sap and then inject a toxin back into the plant. Along the same lines as humans getting a mosquito bite, it's the extra that's injected back in that causes the injury. Symptoms of leafhopper damage start as yellow "V"-shaped areas on the tips of leaves. These areas turn brown or black and then fall out, leaving a "V"-shaped hole on the tip of the leaf. This is a symptom but not the only injury. Large numbers of leafhoppers can kill potato and other plants.

Controls for leafhoppers are warranted with very low numbers. In alfalfa fields, it is recommended to treat when two leafhoppers are caught in a sweep net in alfalfa over a foot tall. Garden treatment options for potatoes include Sevin and rotenone as common insecticide choices available to homeowners. Most trees and shrubs can be treated with Sevin, permethrin or bifenthrin.

[By JOHN FULTON, University of Illinois Extension, Logan County]