These pesky beetles grow to about ˝ inch in length with shiny, metallic green wing covers. It spends much of its life in the soil as a white grub before transforming into a beetle in June. The adult only lives 30 to 34 days but it can do a lot of damage in the time for they are voracious eaters. The grubs feed on plant roots but are generally not a serious problem except on irrigated lawns or golf course roughs.

As with most serious insects or diseases of ornamental plants, the Japanese beetle is an exotic (i.e. not native) critter. They came to America on ships from Asia and landed in New Jersey around 1916. Since that time, they have been moving slowly to the west and are now found in Minnesota and the rest of the Midwest.

Although they feed on a wide range of plants, Japanese beetles have certain "favorites" in their diets. Roses, hollyhock, grape vines and little leaf lindens (Tilia cordata) are often seriously defoliated by Japanese beetles.

Since they feed during the day, the presence of the beetles themselves is a key sign. They are often found in large numbers in and around their favorite plants. Their most favorite part of the plant is the flower bud although they also eat leaves.

Leaf damage shows up as a "skeletonized" pattern. This occurs because they eat the leaf tissue between the veins but not the veins themselves.

Perhaps the key mode of prevention is to use plant species that are not seriously damaged by Japanese beetles.

Unfortunately, there is no quick and easy way to control Japanese beetles.

Nature - Many birds eat Japanese beetles and moles, shrews and skunks feed on the grubs in the soil. Unfortunately, these generally do not significantly reduce populations of beetles.

Milky Spore Disease - This naturally occurring bacterial disease kills the grubs of Japanese beetles in the ground. Unfortunately, there have been no controlled studies that indicated that Milky Spore disease works in northern weather. In Southern states where it has been most effective, it gives erratic results.

Hand Picking - If you have only a few plants to protect and low numbers of beetles, hand picking may work.

Japanese Beetle Traps - Bag traps are generally not effective especially if they are placed near the desirable plants. Studies have shown that they actually attract more beetles to the area than would have otherwise been the case. If using a trap, place it 50 feet or so up wind of the desirable plants to draw beetles away. Do not place them directly in the flower bed or garden.

Soil Treatments - Although the beetles spend most of their time in the soil as larvae (white grubs), treating this stage is often not effective either. The beetles are strong flyers and may travel a mile or more to feed so treating the soil on your property only may not help. If you dig around this fall and find large numbers of grubs ( 5 or more per square foot), it would warrant a soil treatment with a product labeled for grubs of Japanese beetle.

Chemical Sprays - The most common approach includes spraying the adult beetles as they accumulate on desirable plants. This may have to be done several times during the infestation period. Spray only small or valuable specimens that need protection to minimize pesticide use.

Products labeled for Japanese beetle control are often used. An application should provide decent control for 4 to 7 days. Also, do not expect the beetles to die immediately upon being sprayed. It often takes a little time for insecticides to work.

Remember these are generally considered broad-spectrum insecticides which will kill non-target species such as beneficial insects. So, use them only as needed and only on plants being seriously attacked.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Plant Selection and Care - Otherwise healthy plants will generally survive even total defoliation by this pest. Keep trees, and roses well-watered and fertilized to maintain vigor.

Certain plants seem to be more attractive to Japanese beetle than are others. The following are lists of plants that are nearly always fed upon by Japanese beetles and those that are often avoided. Of course, food preferences are dependent on the number of beetles and how hungry they get.

Most evergreen ornamentals, including Abies (Fir), Juniperus (Juniper), Taxus (Yew), Thuja (Arbovitae or White Cedar), Rhododendron (Rhododendron or Azalea), Picea (Spruce), Pinus (Pine) and Tsuga (Canadian Hemlock) are not attacked.

Types of Insects

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