Description
The Japanese Beetle, Popillia japonica, is an invasive pest that arrived from Japan and was first discovered in the US in New Jersey in 1916. Since then, it has established in the eastern US which has a favorable climate and slowly spread Westward across the United States. The USDA currently has a Japanese Beetle Quarantine in the West to protect the agricultural crops and stop the spread of this destructive pest.
Adult Japanese beetles are 7/16” long with shiny metallic green bodies covered with bronze outer wings and tufts of white hair along the sides and back. They emerge from the ground in early summer and feed for 4-6 weeks. The soil-dwelling larvae or grubs are about an inch long when fully grown, C-shaped, white to cream-colored with a distinctive tan-colored head.
Target Crops
Adult Japanese beetles feed on hundreds of plant species, eating the foliage between the veins and giving the plant a skeletonized appearance. The adults are serious pests of flowers, trees, shrubs, fruits, vegetables, and field crops, while the grubs feed mainly on the roots of grasses and are a threat to lawns, golf courses and pastures. Especially prone to damage are roses, grapes, lindens, sassafras, Norway maple, Japanese maple, and plums.
Life Cycle
Adults emerge from the ground in early summer, mate and the females lay their eggs in the top 2-3 inches of soil several times over the summer for a total of up to 60 eggs. Dry soil conditions can decrease the egg survival and because of this, females are attracted to moist grassy areas. The developing larvae or grubs spend the next 10 months in the soil feeding on roots. When the soil cools to around 60ºF in the Fall the grubs move deeper into the soil to overwinter. When the soil temperatures rise above 50ºF in the Spring the grubs move back to the root zone. After feeding for 4-6 weeks, they pupate and surface in June or July, hungry and ready to attack susceptible plants. Adult Japanese Beetles are highly mobile and can infest new areas several miles away.
Beneficial Insect Control
Beneficial nematodes—Both Steinernema carpocapsae and Heterorhabditis bacteriophora are effective for beetle larvae. These parasitic roundworms actively seek out grubs in the soil. The 3-way blend is a good option. These parasites can be applied to the soil to infect and kill soil dwelling pests. While nematodes will not kill adult stages, they will lower Japanese beetle populations by decreasing the larval stages.Nematodes can be used in an irrigation system. Refer to our Beneficial Nematode Tech Sheet for rates and further information.
Insecticide Options - Use in rotation for best results.
For adults on foliage
- Azadiractin or neem oils act as insect growth regulators, antifeedants and ovipositional deterrents. These include AzaGuard and Molt-X.
- For a quick knockdown, use Pyganic with Pyrethrin for an organic adulticide.
- Surround WP is another option. This contains kaolin clay which acts as a mechanical barrier, irritant and disrupts the beetle’s ability to find host plants.
For larvae/grubs below ground
- Mycoinsecticides containing entomopathogenic fungal spores. These include Botanigard, Mycotrol,NoFly and PFR 97. LalGuard M-52 OD used as a drench is especially good for the soil dwelling grub stage.
- Milky Spore contains the bacterium Bacillus papillae and was developed specifically for Japanese Beetle control. Milky spore disease builds up in turf slowly over 2-4 years as grubs ingest the spores. Works best when applied in a community-wide treatment program.
Cultural Control Tips
Removing Japanese beetles by hand may help to control beetle infestations in small plantings. The presence of beetles will attract more beetles. An easy way to remove beetles is to shake them off the plants in the early morning when they are sluggish. Brushing them into a bucket of soapy water will kill them. High value plants such as roses can be covered with a fine netting during peak beetle activity for protection.
Use traps with caution. Japanese beetle traps have proven to attract more beetles than are actually caught, thus causing increased damage to plants.
Selecting the right plants can go a long way in controlling Japanese Beetles. Some species are highly prone to damage, while others are resistant to attack. Following is a list from the USDA on best and worst plants for Japanese Beetle. Most evergreen ornamentals are not attacked (Abies, Juniperus, Taxus, Thuja, Rhododenron, Picea, Pinus and Tsuga)
20 Herbaceous Plants Resistant to Adult Japanese Beetle Feeding
- Ageratum, Ageratum spp.
- Columbine, Aquilegia spp.
- Dusty Miller, Centaurea cineraria
- Begonia, Begonia spp.
- Lily of the Valley, Convallaria majalis
- Coreopsis, Coreopsis spp.
- Larkspur, Delphinium spp.
- Foxglove, Digitalis spp.
- California Poppy, Eschscholzia californica
- Coral Bells, Heuchera sanguinea
- Hosta, Hosta spp.
- Impatiens, Impatiens spp.
- Lantana, Lantana camara
- Forget-me-not, Myosotis spp.
- Pachysandra, Pachysandra spp.
- Poppy, Papaver spp.
- Moss Rose, Portulaca grandiflora
- Showy Sedum, Sedum, spectabile
- Nasturtium, Tropaeolum majus
- Violet, Pansy, Viola spp.
Herbaceous Plants Susceptible to Adult Japanese Beetle Feeding
- Hollyhock, Alcea rosea
- Dahlia, Dahlia spp.
- Hibiscus, Hibiscus moscheutos
- Common Mallow, Malva rotundiflora
- Evening Primrose, Oenothera biennis
- Rose, Rosa spp.
- Grape, Vitis spp.
- Sweet Corn, Zea mays
- Sunflower, Helianthus annuus
- Peony, Paeonia spp.
It’s always a good idea to check with your state department of agriculture for regional Japanese Beetle information, control options, quarantine protocols and pest levels in your specific area.
Sources
Animal and Plant Health Inspection Service, USDA, Japanese Beetle
https://www.aphis.usda.gov/plant_health/plant_pest_info/jb/downloads/JBhandbook.pdf
Japanese Beetles in the Urban Landscape, Entomology, University of Kentucky
https://entomology.ca.uky.edu/ef451
Japanese Beetles in Yards and Gardens, University of Minnesota Extension
https://extension.umn.edu/yard-and-garden-insects/japanese-beetles#life-cycle-1057360