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Chester M Alter Arboretum

Archived News

The Japanese Beetle in Denver

June 13, 2013

Japanese Pine BeetleOver the past couple of years a new insect threat has emerged in the Denver area. The Japanese Beetle was discovered in the Cherry Hills area around 2005 and has slowly but steadily spread. In the last two years the population has exploded on the DU campus and surrounding community. Last summer the population reached damaging levels and is now a real concern.

The Eastern United States has dealt with the beetle for nearly a century now. We know a fair amount about the beetle and there a several approaches to control it. What makes the Japanese Beetle so destructive is that in its juvenile stage, as a grub, it feeds on roots and can be very damaging to turf grass and shrubs. In its adult stage, as a beetle, it feeds on the leaves of a wide range of plants. Typically it is most damaging to roses and garden (food) plants.

You can expect to see the adult Japanese Beetle appear on your plants beginning the end of June through July. Most of the leaf feeding on trees is cosmetic and poses no long term concern. Heavy and repeated infestations can be problematic if the tree or shrub becomes defoliated.

So far we have seen little turf damage at the Arboretum and most of the feeding on trees has been minor. Our roses, tomatoes, grapes and a few flowers have been the most damaged.

For more information about the Japanese Beetle visit:
http://www.ext.colostate.edu/pubs/insect/05601.html
http://www.aphis.usda.gov/plant_health/plant_pest_info/jb/

Marc Hathaway
Arborist of the Chester M Alter Arboretum