A high population of Japanese beetles resulted in lots of white grubs in lawns and gardens, soon followed by hungry raccoons. Photo courtesy Karen J. Kennedy
Three readers sent me photos of their lawns with gouged soil and I observed this condition in several landscapes when on my walks this fall. Blame raccoons. They dig up the turf looking for grubs.
“If you can imagine groups of raccoons foraging for patches of grubs hidden in clumps under the turf, you can understand why they tear up turf when they find their prey. It’s kind if like a cat and mouse game,” said Cliff Sadof, an entomology professor and extension educator at Purdue University.
Raccoons searched for grubs in an irrigated lawn with a lawn service on Indianapolis’ northwest side. Submitted photo
This past summer was really good for Japanese beetles, whose numbers were higher than they had been for several years, he said.
Japanese beetles lay their eggs in lawns and sometimes in garden beds in mid summer. The eggs hatch and by August and September, grubs are wriggling through the soil, munching on roots. Areas that are irrigated regularly are ideal for this task because the soil is soft and easier to wriggle through.
“The raccoons just took advantage of the situation,” Sadof said. “I would recommend inspecting the turf in early to mid August for grubs in the same area that was torn up this year.” Besides a lawn dug up by raccoons, another symptom of a grub infestation is grass that is brown and easily pulled from the ground.
White grubs look a lot alike. From left to right: Japanese beetle, European chafer and June bug. (C) David Cappaert/Bugwood.org
Next August, lift a 12-inch square of turf in areas where you suspect a grub infestation. If you count 10 grubs or more, Sadof recommends treatment. Another way to evaluation is to pull up a plug of grass that you cut with a one-pound coffee can. If there is more than one grub in each plug, treatment may be warranted.
Purdue does not recommend preventative grub treatment, but rather treatment only if grubs are present and only to the infested area. One biological control is beneficial nematodes, which sort of look like skinny worms. These products are approved for use by organic gardeners and farmers. Arbico-Organics.com, PlanetNatural.com and GardensAlive.com are three sources. Treatment is done in August and September when the grubs are moving through the soil.
Another biologic, milky spore disease (Bacillus popilliae), was considered a good option for controlling Japanese beetle grubs, but recent research has cast doubt on that. It only is effective on Japanese beetle grubs. And, a lot of grubs look alike, so if your problem is a masked chafer, another root-munching white grub, using milky spore disease is a waste of money.
For more information, download Purdue’s pamphlet Managing White Grubs in Turfgrass.