There is hardly a gardener out there who hasn't encountered a Japanese beetle. The adult Japanese beetle is a shiny, metallic green with copper-brown wing covers and it’s about 3/8-inch in length. Not all metallic green or copper beetles are Japanese Beetles To be sure of what you’re dealing with, you can look closely at the underside of the beetle and you’ll also see 5 small, white tufts under the wing covers and an additional tuft at the end of the abdomen.
Japanese beetle, (species Popillia japonica), an insect that is was accidentally introduced into the United States from Japan about 1916, probably as larvae in the soil around imported plants. Japanese beetles are known to feed on more than 200 species of plants, including a wide variety of trees, shrubs, grasses, and nursery plants. They are gregarious insects, often feeding in large groups upon a single tree. A swarm of Japanese beetles can denude a peach tree in 15 minutes, leaving nothing but bare branches and the fruit pits. Keep in mind that the adult Japanese beetles are only around for a little over a month, so don’t automatically reach for the sprayer unless they become a serious problem. Some years are better than others.
Efforts are being made to control the spread of this pest. Poisonous sprays control the adult beetles but differ in the length of their protection against re-infestation. Several of the beetle’s natural enemies—species of parasitic wasps and flies that in Japan were found to prey on the larvae—have been imported into the United States, where some of them have become established. Of even greater promise as a biological control is a disease-inducing bacterium, Bacillus popilliae, which causes milky disease in larvae; its use has reduced Japanese beetle infestations in some areas.
Least Toxic Japanese Beetle Controls
There aren’t many natural controls for adult Japanese beetles. Birds aren’t partial to them and although some predatory wasps and flies have been imported, their population isn’t large enough yet to control the Japanese beetle problem.
The most effective natural control is to go into your garden with a jar of soapy water and knock the beetles into it. Japanese beetles feed in groups, starting at the top of plants, so it’s actually pretty easy to fill a jar with them.
Insecticidal soap will kill adult Japanese beetles only if it is sprayed directly on the beetle. It does not have any residual effect, meaning that beetles that aren’t sprayed directly won’t be harmed.
A word of caution about the pheromone beetle traps. They will attract beetles, but you’ll probably wind up with more beetles coming into your yard than you would have without the trap. The original intention of the traps was to track when and how many Japanese beetles were in the area, not as a means of eradication.
Finally, if you have repeated intense infestations, you should check your soil in late summer to see if you have a large grub population. Lift a 1 sq. ft. section of turf. If there are more than a dozen grubs in this small area, consider treating your lawn with some type of grub control. However, not every garden that has a Japanese beetle problem is associated with a lawn full of grubs. The beetles can hatch in your neighbors lawn and find your tasty garden with very little effort.
More Toxic Controls, to be used with Extreme Caution
There are several insecticides labeled for use on adult Japanese beetles, including:
Bayer Advanced Garden Multi-Insect Killer Concentrate
Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate
Orthene Turf, Tree & Ornamental Insecticide
Spectracide® Bug Stop Multi-Purpose Insect Control Concentrate
Spectracide® Triazicide® Soil & Turf Insect Killer Concentrate
These sprays will kill on contact and also have some residual effect. Keep in mind that these sprays will kill more than just the Japanese beetles, so use them only for extreme infestations. You will want to avoid these products if you have a wildlife habitat of any kind! And again, Japanese beetles are only a pest for a little over a month, so don’t over react.
Always read and follow label directions when using any pesticide and Good Luck!