How to control Japanese beetles

Phyllis Heuerman
Frederick County Master Gardener Program

Japanese beetles (Popillia japonica Newman) are a difficult problem. Adult beetles feed on leaves, flowers and fruits of more than 500 species of plants, and grubs are a major turf pest.

The Japanese beetle was first detected in the United States in 1916 in New Jersey. It is believed to have been imported in nursery plants from Japan.

In its native Japan, the beetle's natural enemies keep its populations in check. Here, how-ever, the beetle entered without its natural enemies and found a favorable climate and abundant food supply. Today, the Japanese beetle lives in about half the contiguous states and continues to spread at a rate of 5 to 10 miles per year. It is in all states east of the Mississippi.

Adult Japanese beetles are a brilliant metallic green. Wing covers are a coppery color. Adults feed on fruit trees, ornamental trees, shrubs, vines, flowers and field and vegetable crops. They eat tissue between the veins of leaves and flowers, leaving behind skeletonized tissue.

Adults usually emerge in June and are around for about two months, feeding, mating and laying eggs. Eggs are laid 2 to 4 inches below the ground surface. They hatch in about two weeks, and larvae dig to the soil surface to feed on roots and other organic material. They can cause serious damage to lawns during this period.

In fall, grubs burrow deeper into the ground to overwinter. In the early spring, grubs return to the surface and continue to feed on roots until they eventually emerge as adult beetles. When fully grown, the white grubs are about an inch long and lie in a curled position.

What can we do about them?

If you catch them early or have only a few on your property, you can hand pick them. It is best to pick them in early morning or late evening when they are less active. Drop them into a container of soapy water.

You can use commercial traps to attract and destroy Japanese beetles. However, they are of limited effectiveness unless your population is isolated or the entire neighborhood uses the traps. Place them far from susceptible plant species.

You can suppress the population of Japanese beetles by making your property a less attractive habitat. Plant species immune to or seldom attacked by them. They are highly attracted to roses, crape myrtle, fruit trees, birch and Japanese maples. On the other hand, they are not attracted to magnolias, redbuds, red maples, holly or boxwood. Japanese beetles do not like ageratum, arborvitae, begonias, carnations, coreopsis, daisies, dusty-miller, euonymus, hydrangeas, lilies or snapdragons.

Observe your garden and those of others to see which plants are attractive. In my yard, I find Rose of Sharon, pussywillows, roses and Harry Lauders walking stick are susceptible. My black-eyed Susans, daylilies, echinacea and achillea are not.

There are chemical controls that can be used on adult beetles and grubs. Go to a local nursery, farm supply store or home store and ask for assistance. Read labels carefully to determine which products are effective on Japanese beetles and how to use them.

Sprays for adult beetles are often most effective if applied just before or at the start of an infestation. Grub control is best applied in July and early August when small, young grubs are coming to the surface to feed on lawn roots.

There is an organic control for Japanese beetle grubs, but it takes a while to become effective. Milky spore (Bacillus popillae) may be spread over turf to suppress them. It is a bacterium ingested by grubs.

Spores germinate inside the grub and multiply. The infected grubs die, and more spores are put into the soil at that time.

The disease builds up in turf slowly (over two to four years) as more grubs ingest spores and die. Milky spore works best when applied in community-wide treatment programs.

Read other articles about controlling insects & garden pests

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