If the leaves on your shrubs and trees look like Swiss cheese, they’ve probably been attacked by Japanese beetles. And if your lawn develops brown patches, it could be grubs – the immature form of Japanese beetles.
About Japanese Beetles
Japanese beetles were accidentally introduced to the United States in 1916; they were first found in New Jersey and quickly spread throughout the eastern part of the country. Our climate in the Dayton area is perfect for them and they’ve become a significant problem for many common trees, shrubs, and even turf grass here in SW Ohio.
Adult Japanese Beetles
Adult Japanese beetles are about 1/5” long and are easy to spot with their metallic green coloring, copper-brown wing covers and white spots along the edges.
They’re relatively poor flyers but are still highly mobile, able to move several miles to find new food sources. Usually, though, they stay within a smaller area to feed, mate and lay eggs.
Adult Japanese beetles primarily eat foliage, although they’ll also devour flowers and fruit. They usually feed in groups; you’ll often see whole sections of a plant covered in beetles.
In the Dayton area, you’ll see adults starting to emerge from the ground and begin feeding on plants sometime in June. Over the next 4 to 6 weeks they’ll continue to feed on the tissue between the veins of leaves, giving leaves a lace-like appearance. The leaves on trees or shrubs that have been severely injured sometimes look bronze or tan when seen from a distance.
White Grubs / Beetle Larvae
Soon after adults emerge from the ground in June, they mate and begin laying eggs in the soil. Each female Japanese beetle can lay 40 to 60 eggs during her lifetime.
White grubs hatch in late July to early August and quickly grow to their full size of about 1 inch long. They immediately start feeding on plant roots, with feeding activity reaching its height in late fall. Japanese beetle grubs mostly attack turfgrass roots, although they’ll also feed on vegetables. They’re particularly active in good quality soils and irrigated lawns, where you’ll start to notice brown patches as grass dies off from grub feeding.
Grubs burrow deeper into the soil as the weather cools and spend the winter deep underground. As the soil heats in spring, they resurface and resume eating until pupating into adult (beetle) form in June.
Lawn grub treatments can help somewhat reduce the number of adult Japanese beetles the next year, although they’re still likely to fly in from neighboring properties. Grub treatments are usually done primarily to prevent lawn damage, rather than to control beetles.
Controlling Adult Japanese Beetles
Preventing Japanese beetles from feeding on your plants is an ongoing battle but there are some things you can do to limit the damage.
If the infestation is fairly limited or on smaller plants, you can remove beetles by hand (or shake them off the plant) and dump them into a bucket of soapy water. Early morning is a good time to do this as they’re less active before the sun warms them up.
You can also use netting to cover plants and keep beetles away.
For larger plants or infestations, there are numerous chemical compounds available for Japanese beetle control although they usually require 2-3 applications. A good garden or agricultural center will provide you with many good choices, such as azadirachtin and pyrethrins. When using any of these pesticides, be careful near water and check for environmental information. Many of these chemicals will affect not only pests like Japanese beetles, but also beneficial insects like praying mantids, lacewings, and bees, so be sure you really have no other options before using these chemical controls. Always follow label directions.
For trees and shrubs with a history of beetle damage, or on high-value plants, we can professionally apply a systemic insecticide to prevent Japanese beetle feeding. This preventative treatment can provide season-long control without as much risk to beneficial insects.
Learn more about our Integrated Pest Management approach to insect and disease treatment and prevention here >>
We don’t recommend the use of Japanese beetle traps. Research shows that these traps can attract beetles from many neighboring properties and you don’t want to be the one house in the neighborhood with all of the beetles dining on your plants!
Finally, if you’re considering planting a new tree or shrub in your yard, you can greatly reduce the likelihood of future Japanese beetle damage by choosing one of the plants listed below, and avoiding those most likely to be attacked.
Plant These – Least Likely To Be Attacked
- Red maple (Acer rubrum)
- Silver maple (Acer saccharinum)
- Boxwood (Buxus sempervirens)
- Shagbark hickory (Carya ovata)
- Flowering dogwood (Cornus florida)
- Persimmon (Diospyros virginiana)
- Euonymus – all species (Euonymous species)
- Holly – all species (Ilex species)
- Butternut (Juglans cinerea)
- Tuliptree (Liriodendron tulipifera)
- American sweetgum (Liquidamar styraciflua)
- Magnolia – all species (Magnolia species)
- White poplar (Populus alba)
- Common pear (Pyrus communis)
- White oak (Quercus alba)
- Scarlet oak (Quercus coccinea)
- Red oak (Quercus rubra)
- Black oak (Quercus velutina)
- American elder (Sambucus canadensis)
- Common lilac (Syringa vulgaris)
- Fir (Abies species)
- Juniper (Juniperus species)
- Arborvitae (Thuja species)
- Hemlock (Tsuga species)
- Rhododendron (Rhododendron)
- Yew (Taxus species)
Don’t Plant These – Most Likely to Be Attacked
- Japanese maple (Acer palmatum)
- Norway maple (Acer platanoides)
- Horsechestnut (Aesculus hippocastanum)
- American chestnut (Castanea dentata)
- Hollyhock (Althaea rosea)
- Gray birch (Betula populifolia)
- Rose-of-Sharon, Shrub Althea (Hibiscus syriacus)
- Black walnut (Juglans nigra)
- Flowering crabapple, apple (Malus species)
- London planetree (Platanus acerifolia)
- Lombardy poplar (Populus nigra italica)
- Cherry, black cherry, plum, peach, etc. (Prunus species)
- Roses (Rosa species)
- Sassafras (Sassafras albidum)
- American mountain ash (Sorbus americana)
- American linden (Tilia americana)
- American elm (Ulmus americana)
- English elm (Ulmus procera)
- Grape (Vitis species)
We offer planting services if you’d like your new trees or shrubs to be professionally planted.