I've gotten lots of questions from gardeners in different areas about how to cope with Japanese beetles. The answers may be both encouraging and discouraging for those plagued by these pests. First, the good news.
It may seem as though Japanese beetles hang around ruining your plants for a long, long time. In reality, it's generally about three months. Admittedly, those are the prime growing months in most of the US.
But their time is almost up. By the middle of the month in most areas, the majority of Japanese beetles should be gone till next year. Big sigh of relief, right? Well, yes and no.
It's great to have them no longer chomping on rosebuds and crape myrtle leaves. But they don't actually fly away somewhere else, as birds migrate in the fall. Instead, Japanese beetles lay eggs in the soil, which hatch into white grubs and feed on the grass.
They overwinter four to eight inches down in the soil and late next spring change into pupae, which then hatch into beetles.
To aid in control, it helps to know a bit about the habits of these mature beetles:
They like some plants better than others, as you rose growers know only too well. They prefer plants that are in the sun and don't bother those in the shade very much.
According to the University of Kentucky College of Agriculture , Japanese beetles are more likely to fly into your yard on days when temperatures are between 84 degrees F. and 85 degrees F. and the wind is less than 12 m.p.h.
As you've probably observed, one group of Japanese beetles attracts more. So does the odor of the plants they've damaged.
Putting up traps does catch numerous beetles. Unfortunately, traps also attract more beetles to your yard than they catch (and therefore should be avoided).
So, what are the best methods of control?
First, try avoidance. In areas where infestations are serious year after year, you may want to avoid the beetles' favorites and increase your shade garden.
According to Ohio State University Extension, these are plants that do not attract the metallic-green beetles: 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, and yews.
The USDA Animal and Plant Health Inspection Service adds to that list magnolia, redbud, and burning bush. The site also includes a full discussion of biological controls for adult beetles as well as grubs. (These aren't going to be easy for homeowners to find, however.)
Once, milky spore was recommended as an organic control for controlling the grubs. But tests have been inconclusive in many areas of the country. (Most success has been reported in the East.) Check with your state's Extension Service to see if it has conducted tests in the past few years.
For most of us, the main organic control is removing the beetles from the affected plants and dropping them in a bucket of soapy water to drown.
Like Nancy Szerlag in Detroit, I've never had much success with flicking the beetles from the plant into the bucket. And I can't bear to touch them. But my husband doesn't mind picking them from plants, so this yucky job always falls to him.
In bad years, it has to be done over and over, which is pretty discouraging. Often, though, a bad year is followed by one where the infestation isn't so bad. (A rainy summer, for instance, doesn't provide the conditions the beetles like.)
So, there it is -- the good and and bad. At this point, since there's no real solution, we have try different remedies to lessen the damage.
Added later: If drought could be said to have any advantages, it does lessen the infestations of Japanese beetles, reports the Georgia Cooperative Extension Service.