University of Illinois Extension

“Masked Bandits” in the Lawn

Big brown beetles are more than simply a nuisance that hang around doors trying to get into the house.

“Wait until those irregular patches of brown begin to show up in your lawn later in the summer and then you make the connection,” said Richard Hentschel, Extension horticulturist. “Those grubs we find when we roll up the grass are the larval stage of the Masked Chafer, aka June Beetles, which we swatted away from our doors earlier in the summer.”

He said there are two beetles that homeowners are familiar with, both having a life cycle in lawns. One is the colorful Japanese beetle that has a healthy appetite for a variety of foliage in our landscapes after it emerges from the lawn.

Photo of grub“The other, the Masked Chafer, prefers to feed on the roots of our grass plants,” he said. “It is that feeding in the hot, dry months of August and September that will cause the lawn to brown in those patches.”

To manage the insect, Hentschel recommends starting with understanding its life cycle. It emerges from the lawn in late May into June, giving us its common name of June beetle. This is when they are attracted to patio and front door lights and cling to screens.

“The beetles do feed on grass roots prior to emerging, but in the spring the lawns are growing so rapidly that the roots are replaced quickly and we seldom notice any feeding taking place,” he said.

“Once it emerges, the beetle will find a mate and begin to lay eggs back into the lawn during its short stay above ground. The female Chafer beetle deposits her eggs into small holes which she digs. The beetle can lay more eggs if the soil is softer. More damage is often seen on lawns that are irrigated and in areas near sidewalks, driveways, and downspouts, all of which receive additional moisture from run-off.”

When these eggs hatch and start feeding, the damage shows up. As the small grubs grow, they eat more and more each day until the grass plants cannot replace the roots as rapidly as the grub is eating them.

Photo of beetle“Those areas begin to brown in irregular patterns and you can pull up the lawn as if it were sod,” he explained. “Lawns can live with 10 to 12 grubs per square foot without appreciable damage. More than 12 grubs per square foot and population management becomes necessary.

“Additionally, white grubs are a favorite food of raccoons and skunks and they can do a great deal of damage to the lawn while looking for a meal.”

The key to stopping the feeding damage is controlling grub larvae. If a lawn service is being used, they will likely be scouting for the grub and will apply appropriate soil insecticide as part of the management program. You should check to be sure.

“Homeowners taking care of their own lawns have non-chemical and chemical treatments available,” explained Hentschel. “Since the beetles are attracted to those lawns that are watered, letting the lawn go naturally dormant mid-summer means less eggs will be laid.

“The more trees you have in the yard also means fewer eggs, as the beetles seem to prefer a thicker, fuller lawn.”

When control is absolutely necessary due to high numbers of grubs, homeowners can apply soil insecticides. It is important to remember that the insecticide has to get into the soil where the grub larvae are feeding to work. Homeowner products that contain either imidaclorprid (Merit, Bayer Advanced Lawn Season Long Grub Control) or halofenozide (GrubEX, Hi-Yield Kill A Grub) can be applied in mid-July.

“Make sure you water in the product with enough water to move the active ingredients into the soil,” he noted. “It is easier to apply to a small area and water in before moving to the next. Homeowners will only need to apply these two products once a season.”

Other products available contain trichlorfon (Dylox, Bayer Advanced Lawn 24-Hour Grub Control). Follow label application instructions carefully.

“So this summer, remember how many ‘June beetle’ adults you see, think about how much rain we have had, and keep an eye out for the ‘Masked Bandit,’” he said.