If you have ever walked outside in July to find your roses turned to lace and a cluster of shiny copper-green beetles munching away, you have met the Japanese beetle. They have become one of the most common summer pests across the West Metro, and they are uniquely frustrating because they damage your property twice. Above ground, the adults chew through garden plants and trees. Below ground, their offspring are the white grubs that destroy lawns. Here is how to identify Japanese beetles, understand the damage they do, and actually get them under control.
How to identify a Japanese beetle
Japanese beetles are easy to recognize once you know what to look for. They are about a half inch long with a shiny metallic green head and body, copper-colored wing covers, and a row of small white tufts of hair along each side of the abdomen. You will usually see them in groups, because they release a scent that attracts more beetles to the same plant.
In Minnesota, adult Japanese beetles typically emerge in late June and early July, peak in midsummer, and taper off by late August. That few-week window in the heart of summer is when the feeding frenzy happens.
The double threat: beetles above, grubs below
What makes Japanese beetles such a problem is that they cause two completely different kinds of damage at two stages of life.
As adults, they feed on the leaves of more than 300 plant species. They eat the tissue between the veins and leave behind a lacy, skeletonized look. Favorite targets in Minnesota gardens include roses, linden and birch trees, grapevines, raspberries, and beans.
As larvae, they are the white grubs that live in your soil and eat grass roots, causing the brown, spongy patches that can peel up like carpet. In other words, the beetles chewing your roses in July are laying the eggs that become the grubs wrecking your lawn in August and September. We cover the lawn side of this in detail in our guide to grub control timing in Minnesota.
What Japanese beetle damage looks like
- On plants: leaves chewed down to a lacy skeleton of veins, often starting at the top of the plant where it is sunny
- On flowers and fruit: roses, raspberries, and other blooms eaten ragged, sometimes with beetles clustered right on them
- On the lawn: irregular brown patches in late summer, turf that lifts easily, and animals digging at night to eat the grubs
How to control Japanese beetles
There is no single magic fix, but a few approaches genuinely help.
Hand-pick them. In a home garden, knocking beetles into a bucket of soapy water in the early morning, when they are sluggish, is surprisingly effective. Doing it daily during peak season keeps their numbers and their attracting scent down.
Skip the beetle traps. This is the most common mistake we see. The bag traps you find at the hardware store use a powerful lure that draws in far more beetles than they catch, often pulling beetles from your whole neighborhood right onto your property. Most experts, including University of Minnesota Extension, recommend against them for this reason.
Protect your key plants. For prized roses or young trees, targeted plant treatments during the adult feeding window can reduce damage. Lightweight netting can also shield high-value plants during the few peak weeks.
Attack the grub stage in your lawn. This is the part homeowners miss. Controlling the grubs in your turf with properly timed treatment reduces the next generation of beetles and protects your lawn at the same time. See our grub control service for how the timing works.
The long game: a healthy landscape fights back
You will not eliminate Japanese beetles entirely, since they fly in from all around, but you can keep them from taking over. A healthy, well-maintained lawn and landscape recovers from feeding far better than a stressed one, and managing the grub stage every year steadily lowers the local population over time. Caring for your shrubs and perennials the right way also helps your plants bounce back from summer feeding.
Tired of fighting beetles and the grubs they leave behind? Liberty Lawn & Snow has protected West Metro lawns and landscapes for over 25 years. Get a free quote and we will build a plan that tackles both ends of the problem.