When summer starts people switch from stiff business clothes to raggedy gardening wear, and take to their plants. Their year round dedication to tending and raising gardens is often taken back leaps and bounds by the presence of an uninvited pest.
The Japanese beetle, Popillia japonica Newman, was first discovered in New Jersey in 1916, and has spread to many different places in the US. We have been asked by quite a few different people how they could deal with them organically, so we looked into solutions that have been found to work, and not work.
There are ways to deal with both the adult versions of the bugs, who eat leaves and leave a skeleton of viens behind (below), and the larva, who live under the soil and eat roots.
For the Adults, the first method is hand picking. This is where you go around with a bucket of soapy water and individually drop the beetles in. This seems very tedious when thinking about the large swarms that form in the summer time, but it is an initial method. Beetles scout out new areas for feeding, and release scents that attract other beetles. If you see only a few in an area that has had no previous issues, this method can head off their spread.
Another method is using traps with an attractive scent or floral bait. This method was discouraged, as it was said that unless the entire neighborhood was using traps, it would most likely bring more beetles to the area, and spread the problem.
The third solution was to plant varieties that the beetles don't like. The plants listed on the Ohio State university website on beetle control were "ageratum, arborvitae, ash, baby's breath, garden balsam, begonia, bleeding heart, boxwood, buttercups, caladium, carnations, Chinese lantern plant, cockscomb, columbine, coralbells, coralberry, coreopsis, cornflower, daisies, dogwood (flowering), dusty-miller, euonymus, false cypresses, firs, forget-me-not, forsythia, foxglove, hemlock, hollies, hydrangeas, junipers, kale (ornamental), lilacs, lilies, magnolias, maple (red or silver only), mulberry, nasturtium, oaks (red and white only), pines, poppies, snapdragon, snowberry, speedwell, sweet pea, sweet-William, tuliptree, violets and pansy, or yews (taxus)."
For dealing with the larva, there are two biological controls. The first is using insect parasitic nematodes. Look up Steinernema carpocapsae, there are a few commercial brands available now. It has shown to be moderately effective.
The second is using Bacterial Milky Disease. This is a bacteria that kills grub populations. It takes 2-3 years to build up a spore count in the soil, and during this time insecticides should not be used, as the larva help the spore count develop. This solution requires further testing before it can be shown to be truly helpful.
The beetles do have predators in the US, and in 5-10 years my sources said that the population of Japanese beetles will be more under control. Until that happens, I hope these solutions are helpful to all the hardworking horticulturalists and gardeners out there.
For information regarding chemical solutions, please refer to these sites, which I have used for this post:
Ohio State university: http://ohioline.osu.edu/hyg-fact/2000/2001.html
Michigan State University: http://www.turf.msu.edu/japanese-beetle/