The University of Kentucky's College of Agriculture describes the Japanese beetle as the "most devastating pest of urban landscape plants in the eastern United States." Since the beetles was accidentally introduced in 1916 to New Jersey, the persistent pests have wrecked havoc on more than 300 species of plants across the U.S. Less than ½-inch long, these shiny green beetles with coppery-brown wings cause damage both as adults and in their grub stage.
Japanese beetles are extremely attracted to roses. According to the University of Vermont Extension, roses often "abound in or near sites optimal for oviposition and larval survival." Most varieties of roses are susceptible to infestation. The beetles are attracted to the rose scent and will eat foliage, buds and blooms. The Easy Garden Care website recommends cutting buds in early June and letting them bloom inside to avoid beetle damage.
The American Linden tree, or Tilia Americana, is native to eastern North America. Japanese beetles love to eat linden leaves. Lindens are also susceptible to pests such as aphids, borers, leafminers and scales. Treat linden infestations with a biological insecticide such as milky spore. Milky spore, or the spores of the bacterium Bacillus popillae, infest Japanese beetle grubs and cause them to die out. Milky spore builds up in the soil over two to four years and is most effective if applied community-wide.
The sassafras, or Sassafras albidum tree, is indigenous to the eastern U.S. and is especially tasty to the Japanese beetle. The beetle is considered its main pest. Biological insecticides such as nematodes can help control sassafras infestations. Nematodes, or microscopic roundworms, actively seek out Japanese beetle grubs and inoculate them with bacteria that proves fatal.
The Norway maple, or Acer platanoides, is native to Europe but is well-established in the U.S. Japanese beetles like to snack on the tree's dark green leaves. Japanese beetle infestations can be controlled with applications of Bacillus thuringiensis, or Bt, a naturally-occurring bacteria that's toxic to beetle grubs. Apply Bt to the soil around infested trees.
The Japanese maple, or Acer palmatum, is relatively resistant to other pests but is a favorite of the Japanese beetle. Infestations can be controlled with the introduction of a natural parasite such as Tiphia vernalis, a parasitic wasp. While it's harmless to other garden creatures, Tiphia vernalis lays its eggs on beetle grubs, and larvae will eventually devour its grub host.
Grape plants are especially susceptible to Japanese beetles. Beetles prefer grapevines with smooth, thin leaves such as French hybrid. Affected leaves wither and drop, which can defoliate and injure plants. For low-level infestations, handpick the beetles off leaves in the morning when they're less active. If infestations are severe, perform spot treatments with insecticides containing malathion, permethrin or carbaryl.
Japanese beetles find trees in the genus Prunus, commonly known as plums, very tasty. Though beetles don't generally damage the leaves of mature, established plum leaves, they can destroy fruit crops. A 2007 "Chicago Tribune" article recommended "floating row covers" to combat the beetles. These covers are made from lightweight material that allow sunlight and air to pass through but keeps beetles out.
- University of Kentucky, College of Agriculture: Japanese Beetles in the Urban Landscape
- University of Vermont Extension: Japanese Beetles
- Easy Plant Care: Japanese Beetle Control for Roses
- Maine.gov: Managing the Japanese Beetle
- University of Minnesota Extension: Grape Insect Pests of the Home Garden
- How Do I Kill Japanese Beetles on Roses?
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- Green Worms on Rose Bushes