Japanese beetles and their larvae can cause extensive damage to lawns and gardens. The beetles themselves feed on plants above ground, while their grubs that are living underground damage root systems, often leaving widening spots of dead grass in the lawn. To control the pests, repel them with certain plants, remove plants that attract them, welcome predators that eat or kill them and, if all else fails, resort to pesticides.
Plants that Repel
A preferred method of repelling Japanese beetles is to include plants that repel them in landscaping and gardening plans. Many of these plants are attractive and, when planted near more vulnerable plants as companion plants, they keep the beetles and their grubs away without the risks posed by chemical pesticides. Some plants that repel Japanese beetles include gladiolas, coneflowers, daylilies, Shasta daisies, hollyhock, white mums, tansy, rue, larkspur, garlic, citronella, hibiscus, clematis, sunflowers, peonies, zinnias, climbing hydrangeas and morning glories.
A homeowner or gardener can also repel beetles by excluding items that attract them. Rid the property of asparagus, corn, rhubarb, grape, raspberry and soybean plants, as well as birch, cherry, elm, fruit, sycamore, willow, pin oak, Japanese maple, Norway maple and horse chestnut trees. Exclude also the Virginia creeper and porcelain vines. To further eliminate attractions, remove deadwood from trees and any fruit that falls to the ground.
To kill grubs before than can do damage or mature into Japanese beetles, consider introducing nematodes and bacteria that cause milky spore disease to the property. Available from gardening outlets, these microscopic predators can control the grub and beetle problem for years. Nematodes are tiny worms that prey on the grubs, while milky spore disease is an infection to which the grubs are vulnerable. In addition, spiders and predatory insects will eat Japanese beetles, their eggs and grubs, and a variety of wild songbirds and even ducks will prey on both grubs and beetles. Resist killing helpful bugs and consider offering birds a ration of birdseed to encourage visits.
For a natural solution, consider spraying tobacco juice or gin on plants. Another possible home remedy is a plant spray solution of 1/2 cup of canola oil, 1 tbsp. of garlic powder, 2 or 3 tbsp. of liquid dish soap and enough water to fill a spray bottle. Garlic and citronella sprays also repel beetles, as do the plant-based but toxic chemical pesticide sprays rotenone and pyrethrum.
Japanese beetles are attracted to areas infested with others of their kind. Reduce the number of beetles present, in any way possible, and the attraction is less. Vacuum the adult beetles off plants or knock or pick them off by hand and dump them into soapy water to kill them.
Traps especially intended for Japanese beetles are available in stores, but they often don't work unless the property being treated is expansive. Containing pheromones to attract the beetles to their doom, these bags sometimes make the problem worse by drawing bugs from reaches farther than the property line, essentially attracting them to the property instead of treating only the ones already there. If a property is large enough, however, these traps can be situated to serve as decoys, attracting beetles to locations well away from vulnerable plants.