The Best Ways to Stop Japanese Beetles From Devouring Your Garden
These voracious pests can leave plants with tattered foliage and flowers, plus the larvae can damage lawns. Here's how to keep these bugs under control.
Japanese beetles are invasive insects that first turned up in New Jersey in 1916, and have been leaving trails of destruction as they've spread from there. Now found as far west as the Rocky Mountains, these beetles will treat your garden like a smorgasbord, chewing on many kinds of plants. They also like to invite other Japanese beetles to their feeding frenzy, leaving hole-riddled foliage and flowers (they're especially fond of roses) and distraught gardeners in their wake. Japanese beetles also will destroy fruits and vegetables, and their larvae can damage lawns. Here's how you can evict any of these pesky bugs that show up in your garden and reduce the damage they cause.
When to Look for Japanese Beetles
Before you go to battle with Japanese beetles, make sure you know the enemy. These insects have an iridescent green head and thorax (the part of the body right behind the head) and glossy, copper brown wing coverings. Look for fuzzy white patches along both sides of their abdomen. There are several look-alike beetles that don't have the white spots.
Start watching out for Japanese beetles in May or June, and continue looking for them into August. They are often actively feeding in the morning and late evening. They tend to be most active when temperatures are over 85°F and the air is still, so keep an eye out for new beetles coming into your yard during these conditions. You might not see very many beetles on cool, rainy days, but don’t assume the beetles are gone. A warm, sunny day often will bring a resurgence. A proactive approach that involves checking regularly for them and controlling them right away is essential for managing Japanese beetles.
How to Get Rid of Japanese Beetles
Like brown marmorated stink bugs, Japanese beetles release chemicals called pheromones into the air that attract more beetles. So if you see a few of the bugs around, it probably won't be long before many more join them. That's why quick action to get rid of them will help keep the problem from getting out of control.
Hand-Picking Japanese Beetles
If you've only spotted a few, the safest and most inexpensive route to get rid of them is to pick them off your plants by hand. These bugs actually have a habit of dropping to the ground when disturbed so you can avoid touching them at all by giving your plant a shake and holding a bucket of soapy water underneath to catch them, where they'll drown.
Pesticides for Japanese Beetles
A number of pesticides are available for Japanese beetle treatment, but unfortunately, many of them are harmful to important pollinators like bees and other beneficial insects like ladybugs. Less toxic options like neem-based pesticides can provide good control, as can insecticidal soaps. These need to be sprayed directly on the beetles to work.
Are Japanese Beetle Traps a Good Idea?
The traps, which usually use pheromones and floral scents to lure in the beetles, are intended to draw the ones in your yard to their demise before they can start feeding on your plants. There's been quite a lot of debate on this topic over the years because of fears that the traps can end up making the problem worse. Research on the traps have had mixed results, but generally if the traps are set up and used correctly in a garden setting, they can be an effective option for controlling Japanese beetles.
How to Get Rid of Grubs
While it's the adult Japanese beetles that cause the most damage, their larval form (grubs) can also cause lawn problems. Around August or September, the female beetles will begin laying eggs just beneath the soil surface in grassy areas. They'll hatch out quickly and begin feeding on grass roots, sometimes to the point where you may notice brown, dead patches in your lawn. If you peel up a piece of sod in those areas, you'll likely find the culprits to be white, C-shape grubs. As temperatures cool toward winter, the grubs burrow deeper down to hibernate. In spring, they'll come back up near the surface to begin feeding on grass roots again.
Treating for the grubs will help reduce the number that emerge as adult beetles later. Several chemical pesticides are available, but there are two non-chemical options that are safer options when used around pets, people, and pollinators. These include beneficial nematodes and a product known as milky spore, which is derived from bacteria.
Pick the Right Plants
While Japanese beetles eat hundreds of different plants, there are a few that they tend to avoid. These include the following trees and shrubs: