Emerging pest - Japanese beetles

Published: August 1, 2010

The Japanese beetle is probably the most devastating pest of urban landscape plants in the eastern United States. Japanese beetles were first found in this country in 1916, after being accidentally introduced into New Jersey. Until that time, this insect was known to occur only in Japan where it is not a major pest.

Adult Japanese beetles are 7/16-inch long metallic green beetles with copper-brown wing covers. They feed on about 300 species of plants, devouring leaves, flowers, and overripe or wounded fruit. Leaf feeding results in a skeletonized pattern.

The eastern US provided a favorable climate, large areas of turf and pasture grass for developing grubs, hundreds of species of plants on which adults could feed, and no effective natural enemies. The beetle thrived under these conditions and has steadily expanded its geographic range north to Ontario, west to Missouri and Arkansas, and south to Alabama.

The adults emerge in June, later in the month if cool, and early if the season is hot.

Fortunately for vegetable growers this pest has NOT become significant. However, there is a good chance you will encounter it on some of its other favorite edible crops - raspberries, blackberries, stone fruit and apples. Two other favorite popular plants are roses and hibiscus.

Insects don't read the books about what they are supposed to eat, and there could be times if their population is high and their preferred food supply is short, that they may feed on vegetables. A smaller planting might require a pesticide application to prevent economic damage.

Sevin (carbaryl) is widely available insecticide that is well regarded on its effectiveness against this pest. Trapping the pest is also an option. However, research has shown that the traps attract many more beetles than are actually caught. Consequently, susceptible plants along the flight path of the beetlesand in the vicinity of traps are likely to suffer muchmore damage than if no traps are used at all.