Japanese Beetle

The Japanese beetle is a well-known pest of turfgrass and landscapes in the eastern United States. JB has been reported from 37 different counties in Iowa since 1994, predominantly in the east-central region of the state.

Adult beetles emerge in mid-June through July. They are similar to other Junebugs in general appearance, and 3/8 inch long and 1/4 inch wide. The head and thorax are shiny metallic green, and the wing covers are coppery red. The row of five tufts of white hairs on each side of the abdomen is a distinguishing feature.

Japanese beetle larvae are typical white grubs. They are in the soil from August until June where they feed on plant roots (especially turfgrass) and organic matter. The grubs are C-shaped and approximately 1.25 inches when full grown.

Adult beetles eat the foliage, fruits and flowers of over 300 plants. Foliage is consumed by eating the tissue between the veins, a type of feeding called skeletonizing. Flowers and fruits are devoured completely, often by a horde of a dozen or more beetles at a time.

Control of adult beetles is difficult because they emerge every day for a period of several weeks. Handpicking or screening or high-value plants may be of benefit in isolated situations with limited numbers of beetles. Spot spraying infested foliage of high value plants with carbaryl (Sevin), permethrin (Eight) or cyfluthrin (Tempo) may reduce damage for several days, but multiple applications are required to maintain control. Spraying the adult stage is not an effective strategy for prevention of white grubs.

Several traps using a floral lure and sex attractant are available. Use of these traps is not recommended. Research conducted in Kentucky suggests that they are not effective in controlling moderate to heavy infestations; and they may attract more beetles into a yard than would occur otherwise. The traps may reduce damage and populations when landscapes are isolated from other Japanese beetle breeding areas or when mass trapping (everyone in the neighborhood) is used.

 

Japanese Beetle Host Plant Preferences

One way to limit the impact of adult Japanese beetle defoliation may be to select plants that the Japanese beetles tend to avoid.  The following list of the Japanese beetle's most and least-favored woody plants may be useful to people designing new landscapes in areas infested by this beetle. 

Most Favored by Japanese Beetle

Birch, gray

Elm

Grape

Hollyhock

Horsechestnut 

Linden2, American

Lombardy poplar

London planetree

Malus spp. (crabapple1, etc.)

Maple, Norway, Japanese

Mountain ash 

Prunus spp. (flowering cherry, etc.)

Rose

Sassafras

Walnut, black

Weeds (wild grape, multiflora rose, smartweed, poison ivy)

1Susceptibility of crabapples varies with variety

2Tilia tomentosa 'Sterling' and Tilia americana 'Legend' are less susceptible than other lindens

 

Least Favored by Japanese Beetle

Ash, white, green

Boxelder

Boxwood

Conifers (arborvitae, spruce, pine, fir, yew, juniper)

Dogwood

Euonymus

Green ash

Hickory, shagbark

Holly

Lilac

Magnolia

Maple, red, silver

Mulberry

Oak, white, red, scarlet, black

Persimmon

Poplar, white

Sweet gum

Yellow poplar (tuliptree)