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Extension > Yard and Garden News > Japanese Beetles in Minnesota: Education, detection, and management

Japanese Beetles in Minnesota: Education, detection, and management

Dan Miller, Plant Health Specialist, University of Minnesota Landscape Arboretum

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Photo: Japanese Beetle. Forestry Images. Russ Ottens, University of Georgia.

The Japanese beetle (Popillia japonica) was first detected in the United States in New Jersey in 1916 and has spread throughout most states east of the Mississippi and to parts of Arkansas, Missouri, Kansas, Oklahoma, Iowa, and Minnesota west of the Mississippi. In Minnesota, the beetles were first detected in 1968. Trapping programs conducted by the Minnesota Department of Agriculture (MDA) showed low but consistent numbers from 1991 to 1998. Trapping data in 1999 and 2000 showed a dramatic increase in Japanese beetles with the highest counts occurring in Washington, Ramsey, Hennepin, Dakota, and Carver counties. After trapping in 2002, the MDA concluded that the beetle was too widespread to be eradicated. The beetle was then deregulated and budget cuts shifted the direction of the program so the statewide trapping program was discontinued.

Arboretum exhibit demonstrates integrated control of Japanese Beetles

In recent years, Japanese beetle infestations have become more noticeable in the metro region with many reported cases of damage to golf courses from the white grub larvae feeding on grass roots and damage to ornamentals shrubs and trees (especially roses, grapes, and lindens) from adult beetles. It is apparent that awareness of the pest is growing; however many home gardeners are not experienced or knowledgeable regarding integrated control strategies for the pest. In 2009, the Minnesota Landscape Arboretum obtained a grant from the North Central Integrated Pest Management Center to create an exhibit at the Arboretum to provide updated, relevant IPM information to the public on environmentally safe ways to control the adults and larvae of the Japanese beetle. The display featured a sign located in the center of a plot of turfgrass and roses with general IPM information, a take-home brochure with more detailed information, and a terrarium so visitors could observe the beetles while they were feeding on plants.


Determining the distribution of Japanese Beetle in Minnesota

A secondary part of the grant involved a survey to determine the current statewide distribution of the beetle. In August 2009, an electronic survey was sent to over 300 golf course superintendents via the Minnesota Golf Course Superintendents Association. In October a second electronic survey was sent to nurseries throughout the state via the Minnesota Nursery and Landscape Association. These surveys provided links for respondents to use in properly identifying the beetle. The survey also asked if beetles or grubs had been observed on their golf course or nursery, when they were first observed, the damage levels, and the control strategies employed. Additionally, over 40 University of Minnesota Extension Educators and Master Gardeners across the state were contacted by phone and asked if they had heard of infestations in their areas. Based on previous trapping surveys by the Minnesota Department of Agriculture and our 2009 consensus surveys, it is apparent that the beetles are primarily located in the seven county metro area and southeast toward Rochester and west toward Mankato (Figure 1). Future IPM control efforts should be focused in these areas.

Even though Japanese beetles have been present in the metro area for several years, they were not observed at the Arboretum until 2007. To get a better understanding of the encroachment of Japanese beetles to the Arboretum, a trapping study was initiated in 2009. Twenty traps were set on golf courses and parks in an approximately 10 mile radius round the Arboretum and compared to traps on the Arboretum grounds. Traps were set in each location once a week, left for 24 hours, retrieved, and beetles were counted. Trapping started on July 17th and continued for ten weeks until September 16th. The most remarkable outcome of this trapping project was the noticeable difference between trap counts on golf courses east of the Arboretum and golf courses west of the Arboretum. The average number of beetles per trap for the four golf courses east of the Arboretum was 483.0 while the average number for the two eastern courses was only 2.6. The average number of beetles for the Arboretum's traps was 5.7. Several golf course superintendents indicated that 2009 was either the first year or the second year that they were aware of the beetle's presence. It appears that the Japanese beetle populations are increasing and are continuing to advance further west. 

Figure 1. Status of the Japanese Beetle in Minnesota in 2009 (PDF available: JapaneseBeetleMN2009V3.pdf)

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Methods for decreasing potential damage from Japanese Beetles

Homeowners and golf course superintendents in the metro and southeastern region of Minnesota can decrease potential damage to their ornamentals and turfgrass by scouting and early detection.

Golf courses (and other turf managers) should concentrate their control efforts on the grubs if turf damage is considerable. Imidacloprid and Acelpryn (a reduced-risk insecticide) have proven to be effective.

Homeowners can control small infestations of adult beetles by picking them off the plants and dropping them into soapy water or rubbing alcohol. Pheromone traps are not recommended as beetles may miss the trap and land on nearby landscape plants, causing damage.

If damage is beyond tolerable levels, conventional insecticides may become necessary. Imidacloprid and residual pesticides like pyrethroids are effective for adults but should only be used where infestations are found and not used as preventative treatments.

Homeowner's can treat grub damage using biorational control with products containing halofenozide an insect growth regulator or with beneficial nematodes. It is necessary to confirm that turf damage is caused by white grubs and not by other turf diseases before implementing control methods.


Detection of Japanese Beetles in new counties

If beetles are found in counties not marked on the map in Figure 1, please let us know by sending specimens including capture location and date to Jeff Hahn at Department of Entomology 236 Hodson Hall, 1980 Folwell Ave., St. Paul, MN 55108 or send digital images to hahnx002@umn.edu.



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