Plant News - Japanese Beetles

Parkians beware! The Japanese beetle (Popillia japonica) has recently been spotted in Denver. The beetle was first introduced to the United States via a nursery in New Jersey in 1916. Since then, it has spread across most of the eastern US. The beetle has yet to really become established west of the Mississippi, but only time will tell if it's here to stay this time.

Japanese beetles are major agricultural pests. They damage plants by eating the leaves in between the leaf veins. They seem to particularly target members of the rose family, including roses, apples, peaches, pears, plums, cherries, strawberries, blackberries, and raspberries. However, they're not very picky, and will also eat tomatoes, peppers, beans, peas, grapes, hops, corn, blueberries, currants, asparagus, and rhubarb. They'll also eat trees and flowers, including maples, birches, lindens, oaks, willows, cottonwoods, aspens, asters, hydrangeas, sunflowers, and even poison ivy. However, Japanese Beetles actually spend 10 months out of the year underground as grubs, where they feed on grass roots. They can cause dead spots in otherwise healthy lawns.

Though there are several pesticides and biocontrol products available that can control the beetle's population, the best offense is a good defense. By keeping trees and shrubs healthy, interplanting resistant species, and avoiding watering your lawn in late June and early July, you can make your yard less attractive to Japanese beetles, and minimize what damage they do.

For more information, check out the USDA website, or this USDA pdf.