Japanese Beetle Prevention

Overview

Japanese beetles undergo complete metamorphosis, starting as grubs in your lawn and developing into round, metallic- sheened, hard bodied beetles. These hungry beetles enjoy a wide variety of plants and can cause some serious damage at both their larval and adult stages if they are left to flourish unchecked. 

Grubs

Description/ Identification

• White larvae that feed on the roots of grasses 
• Creamy white body with a dark head and the legs on the thorax are well developed
• Grubs thrive in short, well irrigated lawns

Damage

• Japanese beetle larvae primarily feed on grass roots

Prevention/ Treatment Options

• Keep your lawn mowed at a taller height
• Adjust your watering system allowing for your turf to dry between waterings (this will also reduce a variety of fungal issues and make your lawn more heat resilient!)
• Attract beneficial insects like Tiphia wasps that help control Japanese beetle Grub population In routinely mowed lawns
• Use pest control products like GrubEx or Milky spore (both must be applied in the late spring or early summer, typically May through Mid July in Fort Collins) 

Adult

Description/ Identification

• Measure about ½” in length. 
• Generally metallic green with coppery brown wing covers 

 Damage

•  Japanese beetle adults feed on fruit, foliage, and flowers of over 300 plant species. 

Prevention/ Treatment Options

• Hand pick Japanese beetles and place them in a small bucket of soapy water
• Pheromone traps can be used in some situations, however these must be placed far from any crops you are trying to protect.
• If necessary, insecticides can be used to manage the adult stage. 
• Ask one of our staff members for assistance in determining the best treatment option for you.

Resources

Japanese Beetles – Fort Collins Nursery

Japanese Beetle – 5.601 – Colorado State University Extension

Japanese Beetle, Popillia japonica – Colorado State University College of Agricultural Sciences

IPM Case Study: Japanese Beetle – University of Minnesota

Originally published on April 3rd, 2025.