Japanese beetles chewing on your plants? Here’s what works, and one ‘remedy’ to avoid
With enough warm summer days upon us, many gardeners in the area are beginning to sing their woes about the dreaded Japanese beetle. Generally numerous, these metallic green and brown insects are known to feed on over 300 species of plants, including roses, ornamental trees, flower beds, orchards, vineyards and vegetable gardens.
When they’re done feeding, not much is left of your plant’s foliage aside from the skeletonized remains of leaves. What’s more, controlling them is tedious and often sporadically successful. So, what do we know about these insects? What can be done to control them successfully?
Japanese beetles were first introduced to the United States at the 1916 World’s Fair in New Jersey. In short, they made their way onto incoming freight. Since then, the pests have progressively expanded to every state east and west of the Mississippi in non-arid locales capable of sustaining them.
Though they are only alive in their beetle form for about six weeks in the summer, they have a year-long lifecycle, including several pupal stages as grubs in the soil. Their summer emergence is when they become truly damaging to plants.
The best method for mitigating Japanese beetles is still the old standby of manual hand removal, which involves dropping the pests into soapy water. Though tedious, this is most effective at eradicating the pest from a plant without damaging other insects that may be present.
The chemical active ingredients that can be used to treat Japanese beetles are cyfluthrin, bifenthrin, and cyhalothrin. However, these ingredients are also known to be detrimental to the pollinators and beneficial insects you want (and need) for your gardens to be productive.
Though not foolproof by any means, the best method to apply these and avoid your beneficial insects and pollinators is to apply early in the morning or later in the evening, when the insects are resting and not flying around. The products then require re-application every two to three weeks to be effective. Neem products and pyola oil have also been effective at deterring Japanese beetles, with the caveat that they only offer three to four days of protection before needing reapplication.
Those who have heard of Japanese beetle traps may be interested in incorporating them into gardens. Unfortunately, this practice should be avoided unless your garden is in a wide-open space. The purpose of these traps is to draw in beetles using pheromones.
The traps are very effective and will cause a full-blown infestation if not located correctly in an area large enough to accommodate this added influx of pests. If used, the traps should be placed far away from the gardens or plant specimens you are trying to protect. However, placing traps and reapplication of chemicals may be just as tedious as hand-picking, making the latter the most effective and desirable control.
Anthony Reardon is a horticulture agent with Kansas State University Research and Extension. Need help? Contact the Johnson County Extension gardening hotline at 913-715-7050 or email garden.help@jocogov.org.
