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What do Japanese beetles eat? What do they avoid? And should you care?
Dear Avant Gardener, Japanese beetles have become a big problem in the upper Midwest. I stopped growing food because of their damage. They lay their grubs in turf and ruin the grass. Do you know of a native ground cover that would be a good substitute in Minnesota? — Bested by Beetles, St. Paul, MN
I like your thinking! Replacing plants on which Japanese beetles are feeding makes so much sense. (And for readers in the west, replacing turf may slow their spread; see “Why?” below.)
In a natural landscape, plants come and go and move around. Unfortunately, much horticultural advice is counter to this natural ebb and flow. Gardeners often take draconian measures — like spraying pesticides — to prolong the lives of favored species like roses and turfgrasses.
Collectively, Americans spend hundreds of millions of dollars a year to control Japanese beetles, including tens of millions for pesticides to kill grubs that eat the roots of turfgrass.
Today, the Japanese beetle is the most widespread turf-grass pest in the United States. Efforts to control the larval and adult stages are estimated to cost more than $460 million a year. Losses attributable to the larval stage alone have been estimated at $234 million per year — $78 million for control costs and an additional $156 million for replacement of damaged turf. — USDA
Disrupting the lifecycle
Your suggestion to replace plants important to the Japanese beetle lifecycle makes more sense. In addition to replacing turf, you might consider removing and replacing plants that adult Japanese beetles eat near the affected turf. This would disrupt their lifecycle and possibly eliminate the grubs that currently plague your grass.
Extensive sampling of fairways on one central New York golf course suggested that patches with perennially high JB grub densities tended to occur near plants that attracted adult feeding aggregations. — Biology and Management of the Japanese Beetle
Unfortunately, unlike native insects, most of which are specialists that eat specific native plants, Japanese beetles eat hundreds of plants, both native and non-native. Still, they avoid hundreds more.
Japanese beetles are among the most polyphagous of plant-feeding insects. Adults feed on foliage, fruits, or flowers of >300 species of wild and cultivated plants in 79 families. — Biology and Management of the Japanese Beetle
Remove these Japanese beetle favorites
The following favorites are worth replacing when possible, especially if you have grub-infested turf nearby. Some favorite adult Japanese beetle foods like crape myrtle, crabapple, rose of Sharon, and Norway maple are also invasive, so you’ll be helping protect wild places by removing them.
Woody Plants Adult Japanese Beetles Love Most
American mountain-ash (Sorbus americana)
Apple, crabapple* (Malus spp.)
Birch (Betula spp.)
Crape-myrtle* (Lagerstroemia indica)
Japanese maple (Acer palmatum)
Linden (Tilia spp.)
Norway maple* (Acer platanoides)
Pin oak (Quercus palustris)
Plum, apricot, cherry, peach (Prunus spp.)
Raspberry, blackberry (Rubus spp.)
Rose (Rosa spp.)
Rose of Sharon* (Hibiscus syriacus)
Sassafras (Sassafras albidum)
Virginia creeper (Parthenocissus quinquefolia)
Perennials Adult Japanese Beetles Love Most
Common mallow (Malva rotundiflora)
Dahlia (Dahlia spp.)
Evening-primrose (Oenothera biennis)
Hibiscus (Hibiscus moscheutos)
Hollyhock (Alcea rosea)
Strawberry (Fragaria spp.)
Clematis (Clematis spp.)
Gladiolus (Gladiolus spp.)
Sunflower (Helianthus annuus)
Morning-glory (Ipomoea purpurea)
Cardinal flower (Lobelia cardinalis)
Peony (Paeonia spp.)
Zinnia (Zinnia spp.)
(If you want to delve further, check out this more comprehensive list of Japanese beetle host plants.)
Replace them with native plants Japanese beetles avoid
There are hundreds of native plants that Japanese beetles avoid, including many of my favorites. Please plant only native species to support beneficial native insects. That may take some work; exotic species within these genera are often easier to find than natives — e.g., Korean dogwood, English holly, Japanese pachysandra, and European forget-me-nots. Use the links to U.S. native range maps for the genera to identify species native to your area (light green) and avoid exotic ones (blue or red).
Native Trees and Shrubs Resistant to Adult Japanese Beetles
Arborvitae (Thuja spp.)
Ash (Fraxinus spp.)
Bearberry (Arctostaphylos uva-ursi)
Dogwood (Cornus spp.)
Hemlock (Tsuga spp.)
Hickory (Carya spp.)
Holly (Ilex spp.)
Hydrangea (Hydrangea spp.)
Jersey tea (Ceanothus americanus)
Juniper (Juniperus spp.)
Magnolia (Magnolia spp.)
Northern red oak (Quercus rubrum)
Persimmon (Diospyros spp.)
Pine (Pinus spp.)
Red maple (Acer rubrum)
Red mulberry (Morus rubra)
Redbud (Cercis spp.)
Spruce (Picea spp.)
Sweetgum (Liquidambar styraciflua)
Tulip poplar (Liriodendron tulipifera)
Yew (Taxus spp.)
Perennials Native Plants Resistant to Adult Japanese Beetles
Remember, check the linked U.S. range maps to find species native to your area (light green). The examples are commonly available, as well as native to St. Paul.
Alumroot (Heuchera spp., e.g., Heuchera richardsonii)
Asters (Symphyotrichum spp., e.g., Symphyotrichum novae-angliae)
Columbine (Aquilegia spp., e.g., Aquilegia canadensis)
Coreopsis (Coreopsis spp., e.g., Coreopsis palmata)
Larkspur (Delphinium spp., e.g., Delphinium carolinianum)
Mint family (Mentha, Monarda, Salvia, e.g., Monarda fistulosa)
Pachysandra (Pachysandra spp.)
Pussy-toes (Antennaria spp., e.g., Antennaria neglecta)
Rudbeckia (Rudbeckia spp., e.g., Rudbeckia hirta)
Violet (Viola spp., e.g., Viola sororia)
Wild ginger (Asarum canadense)
Groundcovers to replace turf
Back to your original question, the lower-growing plants above could act as groundcovers — evergreen bearberry and Canada yew; shade-loving alumroot and wild ginger; and adaptable violets and pussy-toes.
If what you really want is a grassy look that takes foot traffic, Pennsylvania sedge and path rush are good options. See “Related Resources” below for more information. Whatever you do, DO NOT plant red or white clover (Trifolium pratense or repens); they are Japanese beetle host plants.
— The Avant Gardener
P.S. Regular readers, please consider upgrading to a paid subscription so I can reach more people interested in the art and science of ecological landscaping.
Why, How, Wow!
Japanese beetles are yet another reason to replace turfgrass, even in uninfested areas. They are apparently here to stay, according to the USDA. And irrigated turf grass can facilitate the spread of Japanese beetles to arid climates where they would not naturally thrive, such as the American west. According to the most frequently cited academic paper on Japanese beetles,
Finally, we suggest that analyses (e.g., 4, 46) that have projected the JB's probable ultimate spread in North America and elsewhere in the world may be overly conservative. Such models match the pest's temperature and soil moisture requirements with seasonal rainfall and other regional climatic factors. They do not take into account the expanses of irrigated turf and crop lands that now characterize many of the semiarid regions of United States that formerly were too dry to be suitable for the JB. This patchwork of suburban, grassy oases and irrigated agricultural lands may facilitate the JB's spread into Nebraska, Kansas, Oklahoma, Texas, and irrigated areas of the Great Basin; such spread has already occurred in parts of Japan (11). In southern and central California, extensive irrigation makes large areas vulnerable to the JB's establishment, and the climate of western Oregon, Washington, and southwestern British Columbia also is suitable (4, 46). — Biology and Management of the Japanese Beetle
Planting diverse native plants will attract species that prey on the destructive beetles. These predators include both generalists and scoliid wasps.
Endemic, generalist predators, especially ants, staphylinids, and carabids, cause substantial mortality of JB eggs and young larvae. Moles, skunks, and racoons prey on the grubs, but their foraging is often highly destructive to turf. European starlings, crows, grackles, gulls, and other birds feed on the grubs or adults. — Biology and Management of the Japanese Beetle
Scolia dubia, a native scoliid wasp, is known to prey on Japanese beetles. Female scoliid wasps enter their underground burrows and lay an egg on each grub. When the wasp larva hatches, it consumes the grub. You can attract scoliid wasps to your property by planting the nectar-producers they favor.
The adult wasps drink nectar from flowers, usually flowers that have short tubes, arranged in dense clusters that provide a landing platform for the wasp. Mountain mints and many aster family members fit this description. They seem especially partial to goldenrods and bonesets, in addition to the mountain mints. — The Natural Web
I’ve recently fallen in love with common rush (Juncus effusus), a taller relative of the turfgrass replacement I recommended to my subscriber (Juncus tenuis).
Common Rush is the most widespread rush worldwide and the species that is cultivated most often. A fine accent near ponds, it is considered a wetland plant, but can thrive in medium soils. — Prairie Moon Nursery
I took this picture of Japanese beetle-resistant common rush at Paynes Prairie Preserve State Park in Gainesville.
For more on sedge and path rush as a turf replacement, read Love the Look and Feel of Grass? These Ground Covers Are for You. For moist, shady areas, read You Can Do Better.
Removing trees? Don’t bother removing the roots and consider leaving a stump or a snag. Learn how in 1,000 Reasons to Love a Snag.
Curious about a plant not listed above? See the list of 390 plants Japanese beetles avoid, starting on page 12 of this article from the USDA.
Thanks for this, we’re in Vancouver Canada and have just started to see Japanese beetle. Our government is attempting to contain and spray them at the moment. But, I think we all know just how elusive chemical-led control is. So I’m happy to see some great alternatives here!
Thank you for this thorough research! Lots to think about and make changes over time. I like the idea of the Pennnsylvania sedge in some of our more shaded yard and will start with that. Will also plant more perennials that deter the JB. I am interested in looking into why white clover is not recommended as it has become a rather hot item up here in Minnesota as a turf replacement. Thanks, Heather! Looking forward to next week's edition.