Japanese beetle control and a pumpkin reminder

By John Fulton

[June 23, 2011]  A few Japanese beetles have shown up in the area. This makes them about a week earlier than normal. Whether these are local hatches or tagalongs from southern areas doesn't much matter. They are coming.

Japanese beetle adults have a half-inch 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. 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 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 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.

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 also 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.

Pumpkin reminder

If you haven't sown pumpkins for fall decoration, the correct timing is usually around Father's Day. Vining pumpkins need at least 50-100 square feet per hill, with the larger pumpkins requiring the larger area. Hills should be five to six feet apart and rows of hills should be 10-15 feet apart. Each hill should have about four seeds per hill, planted about an inch deep. The miniature varieties such as the Jack-Be-Little are sometimes grown in rows with seeds planted every eight to 12 inches, then thinned to about two feet apart in the rows.

Fall decoration pumpkins should be cut after the color is acceptable but before the vine dries, in order to have a good stem attached to the pumpkin.

[By JOHN FULTON, University of Illinois Extension]