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Japanese Beetle

Japanese Beetles feeding on leaf
Japanese Beetles feeding on leaf.
Emerging as a nuisance in St. Paul, the Japanese beetle is a destructive, exotic pest harming turf, shrubs, and trees. Thought to be established only in isolated areas within Saint Paul, the beetle has spread to encompass a broader area in the city. Currently, the City of Saint Paul does not actively manage Japanese beetles. 

About 1.5 cm long and 1 cm wide, the Japanese beetle has a metallic green head and a copper-colored sheath that protects its wings. Although considered to be lazy, slow fliers, adults are capable of flying as far as 700 meters in five hours.

In a large infestation, adult Japanese beetles skeletonize foliage (see picture at right), leaving only the veins of leaves intact. One alarming fact about their feeding is that they are known to feed on over 300 host plants, including linden, birch, and crabapple varieties. Fortunately, most trees are able to recover from this damage and will typically produce new growth once the adult beetles finish feeding. However, plants that are stressed from other factors may not be that lucky. 

At the moment, there exists no "silver bullet" to control Japanese beetles. Evidence from other states has shown that once Japanese beetles establish an area of breeding and feeding, they tend to remain; however, population size can often fluctuate from year to year resulting in many beetles one year and very few the next. Before starting any control program, it is important to conduct a survey to measure the magnitude of the infestation. Several insecticides are available but depend on the timing of application, the number of beetles in the area, and  the stage of life the beetle is in. Less invasive biological controls, such as certain nematodes and parasites, also exist. It can be effective to select landscape and garden plants that Japanese beetles do not feed on to minimize an infestation and the resulting damage. Through various well-timed management techniques, Japanese beetle damage can be minimized, though not eradicated in most cases.

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