Japanese beetle management: Daily shakedowns work best

By Jean English | Aug 20, 2011
Photo by: Jean English Japanese beetles congregating, annihilating and copulating on a grape leaf.

Japanese beetles are such party animals. They like to congregate on the tops of leaves or inside flowers, chowing down on the tissues and skeletonizing leaves, and they copulate like crazy. The adults show up in mid-June in Maine and carouse through September.

Among their favorite feasts are roses, grapes, plums, raspberries, linden, crab apples (although some varieties are resistant), apples, Japanese maples, Norway maple, horse chestnut, hollyhock, gray birch, American chestnut, rose-of-Sharon and black walnut.

They tend not to bother dogwoods, red oak, butternut, ash, red maple, silver maple, magnolia, junipers, spruce, lilacs, clematis, forsythia, box elder, spruce, fir, hemlock, holly, pine, rhododendrons and yews.

I prefer to manage this pest manually. First thing in the morning, each morning if possible, when dampness on beetles’ wings and cool temperatures limit their flying, knock the beetles off plants and into a container of water with a few drops of soap in it — just enough to break the surface tension of the water so that the beetles become submerged and drown. If possible, spread a cloth or tarp under heavily infested plants, knock the beetles down onto that and then dump them into soapy water.

An alternative — also first thing each day — is to vacuum beetles with a Shop-Vac on a long extension cord or with a rechargeable hand-held vacuum. Then, dump the contents of the vacuum into a bucket of soapy water. This method will make a mess in the vacuum cleaner, so consider dedicating a hand-held vacuum to beetle, and other insect, control.

Note that the presence of Japanese beetles attracts other Japanese beetles (party animals, remember?), so getting rid of some beetles can have a greater effect than you might expect.

You can cover valuable plants with cheesecloth or insect netting to exclude beetles. Dubois Agrinovation in Quebec sells a product called ProtekNet that should exclude Japanese beetles from plants. It’s expensive but can last at least five years. These covers have to be removed for pollination, though, so they offer only partial control.

Japanese beetle traps, sold at garden centers, are not recommended. They can attract many more beetles to your garden than they capture. If you do use them, place them at least 50 feet from plants you want to protect, recommends UMaine Cooperative Extension.

If you turn over a patch of damaged lawn and find 10 or more Japanese beetle grubs per square foot, you might apply the beneficial nematode Heteroditis bacteriophora (Hb, for short) in late summer or early fall. These nematodes may give some control of the grub stage.

Grubs, the larval stage of the beetle, are white, C-shaped, and a little over an inch long at maturity. They feed on the roots of grasses and other plants. Note, however, that adult beetles can fly in from some distance — miles, even — so treating grubs in your own turf won’t necessarily control adult populations on your plants.

Milky spore disease, another biological control, does not work in Maine, according to entomologists here.

Some animals provide partial control of Japanese beetles. A tachinid fly (Istocheta aldrichi) called the “winsome fly” lays eggs on the pronotum (the plate-like structure just behind the Japanese beetle’s head), and when these eggs hatch, the larvae feed on the insides of the beetles. These flies help control beetles early in the season but are gone later. If you see a beetle with small white eggs on its pronotum, don’t kill it.

Among birds reported to eat Japanese beetle adults are the grackle, European starling, cardinal, meadowlark, catbird, English sparrow, wood thrush, brown thrasher, red-headed woodpecker, blue jay, king bird, scarlet tanager, mockingbird, robin, pheasants, chickens, ducks, geese and guineas. Canada geese, starlings, grackles, crows, gulls and chickens eat Japanese beetle grubs.

So put birdbaths, birdhouses, feeders and plants that attract birds in your landscape, and consider moving poultry around your lawn in a portable coop (a “chicken tractor”). Extensive feeding by poultry and crows (and possibly other birds) can damage turf, however.

Raccoons, opossums, moles and skunks also eat Japanese beetle grubs — and poke away at your lawn in the process.

Among organically approved insecticides, neem, pyrethrins and insecticidal soap can be temporarily effective. You can also coat valuable plants with kaolin clay, if you have the patience to repeat applications after rains and don’t mind seeing foliage with a chalky coating. Be sure to follow directions when using these products.

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