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Japanese Beetle

June 22, 2005

Japanese beetle has arrived in central and southern Illinois. Beetles were reported from Assumption on June 15 and were found in the Clinton and Urbana areas on June 16. We normally do not expect to see Japanese beetle adults until the last week of June in central Illinois. Their emergence 10 to 14 days ahead of schedule is similar to the early emergences of other insects this year. We anticipate a heavy emergence of beetles this year, primarily because the weather has been appropriate for their development and survival. Factors that reduce beetle numbers are hot, dry soils in the fall and deep freezing into the soil during the winter. Neither of these occurred in the past year. The lack of rainfall, at least in central Illinois, during May would have had little effect on Japanese beetles because they would have been in the pupal stage for most of the month.

Adult Japanese beetles are 3/8- to 1/2-inch long. They are metallic green with coppery wing covers. They feed heavily on linden, birch, crabapple, rose, grape, brambles, willow, buckeye, and many other trees and shrubs. They are sun-loving beetles, feeding primarily on the upper surface of the leaves at the top of the tree or shrub. For that reason, damage tends to occur first at the top of the plant and works its way down. They eat through the upper leaf surface and interior mesophyll tissue, leaving the lower epidermis to dry and turn brown. They also eat holes through the leaves as well as consuming entire leaves.

These beetles fly to new hosts about every 3 days, typically flying 1 to almost 3 miles. For this reason, control of adult beetles has little effect on the amount of injury by Japanese beetle white grubs to nearby turf. Because beetles flying to new hosts are attracted to plants that have been fed upon previously, treatment or hand-picking when the beetles first appear helps reduce later damage. When disturbed, the beetles fold their legs and drop from the foliage. Holding a jar containing rubbing alcohol or soapy water under the beetles and then poking at the beetles once they are in the jar causes them to drop into the liquid and be killed.

Although beetles can be found into early October, their numbers remain high enough to cause significant feeding damage for about 6 weeks. Japanese beetles can be controlled with foliar applications of carbaryl (Sevin) or cyfluthrin (Tempo). Each insecticide typically provides control for 10 days to 2 weeks, so at least three applications will be needed to protect plants from severe feeding damage. Neem or azadiractin is repellent to the beetles, but it appears to perform better when applied before the beetles become numerous. Repeated applications are needed. Limited research with Japanese beetle traps has shown increased damage on plants in trapped areas. Although many beetles are trapped, it appears that the traps attract many beetles from a distance that then feed on nearby plants rather than flying into the trap.

Author: Phil Nixon


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