Japanese beetles return to wreak havoc in the garden. Here’s what to do, and not do
“The Return of the Japanese Beetles” sounds like a horror movie. But unfortunately, these beetles have returned to devour our landscapes for another summer of terror.
Once a seldom seen insect, they are now well established in the Kansas City area, so expect this feeding frenzy to replay every summer.
The adult Japanese beetle is shiny green/bronze with white dots and feeds on over 300 plant species. They love roses, grapes and linden trees but feed on green beans, hibiscus and crepe myrtles as well. Few garden plants are exempt from their destruction.
The good news is rarely do they kill the plant. Instead, the foliar feeding causes the plant to look unsightly. The bad news is controlling them is difficult.
Many gardeners just let them have their way for the four to six weeks that they are active. Tolerance is a challenging trait to practice. Instead, many reach for chemical controls to reduce the foliar and flower feeding.
Products labeled for control include Cyfluthrin, Bifenthrin and Cyhalothrin, which may last around two weeks. Organic Neem Oil can be used but must be reapplied about every three days. Be aware, these insecticides also take their toll on the beneficial insects like bees and butterflies.
An organic option to control Japanese beetle is removing them by hand. While time-consuming and not a fun task, it is effective. Knock the beetles into a bucket of soapy water to meet their demise. The ideal time is in the cool of the morning. They are sluggish earlier in the day and become more active as the day gets hotter.
Internet rumors caution about knocking the shiny beetles to the ground and stepping on them. Some believe crushing releases a pheromone scent attracting more beetles. Research has found that crushing does not draw more feeders. If it makes you feel good to stomp them to death, go right ahead.
It is true that Japanese beetles are drawn to an area by the use of pheromones. Japanese beetle traps, or lures, are baited with the scent to attract the adults. They fall into the trap, cannot fly out, and are left to die. These traps are available for purchase and and effective in attracting the beetles.
But the problem with the traps is they attract more beetles than they catch. Placing a trap in your garden may unknowingly increase feeding on the same plants you are trying to protect. If you want to experiment with a trap, put it as far away from desirable plants as possible. These traps are not recommended for suburban lots.
Japanese beetles have a grub stage, which can damage lawns. Luckily grub control treatments rid the lawn of these grubs and reduce damage. Controlling the grubs in your lawn will have no effect on the number of adults feeding on your plants because they fly in from surrounding areas.
When it comes to the annual appearance and feeding of this destructive pest, the best advice may be to remember the age-old saying, “This too shall pass.” Patience is a virtue we can practice in the garden.
Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.