It’s a bit later than in recent years, but we are beginning to see one of our most dreaded yard and garden insects – the Japanese beetle. I spotted a few in Steele and Rice counties the week of July 8, but hadn’t seen any earlier than that.
They are emerging a little later than usual, perhaps because of the periods of cooler weather this year. But, once they’re out in full force, you may spot them on any of over 300 species of plants in our yards and landscapes. They are generalist feeders, and can quickly defoliate plants once they begin munching.
The Japanese beetle (Popillia japonica), should not be confused with “Asian beetles” which is what some people call non-native lady bugs. Asian lady beetles are red or orange, with black spots. Japanese beetles are much larger, at approximately 1/3-to-1/2 inches long. They have a metallic green head and thorax (the area behind the head) with copper-brown colored wing covers. The sides of the beetle’s abdomen have five patches of white hairs and the tip of the abdomen has two patches of these hairs.
Though Japanese beetle adults consume many different plants, some of their favorites include roses, grapes, apple trees, and basswood trees. Larvae feed on the roots of grasses and can be a problem for yards and turf, but that mostly occurs only in large expanses of turfgrass, like golf courses or especially large lawns.
Japanese beetles can be a significant landscape pest and difficult to tolerate, because their damage is typically extensive and ugly to look at. Japanese beetles typically don’t kill the plants they’re eating, but they leave behind skeletonized, sometimes sickly-looking plants. They skeletonize leaves by feeding on tissue between the major veins giving them a lace-like appearance. Then, damaged leaves turn brown and may fall off.
Fortunately, adult Japanese beetle damage usually affects only the appearance of plants. Healthy, mature trees and shrubs, and even flowering plants, like roses, can tolerate a lot of feeding without significant, long-term injury. Even fruits, vegetables, and herbs can tolerate limited leaf feeding, but severe damage may affect plant growth and reduce yield. Japanese beetle can be a pest in soybeans and other agricultural crops as well, though damage does not typically warrant treatment at this point. The main plants to worry about are usually young or unhealthy plants. They may be stunted, injured or even killed from persistent feeding.
To reduce injury to plants, you can regularly harvest beetles off plants (drop them into soapy water to terminate them) during July and August. This can decrease feeding and prevent the beetles from attracting even more Japanese beetles to your property.
For more information and for treatment options, visit extension.umn.edu/yard-and-garden-insects/japanese-beetles or contact Claire LaCanne at 507-332-6165 or firstname.lastname@example.org.