July 28, 2005 | By: Terri McLean

When it comes to this year’s Japanese beetle invasion, there’s good news and there’s bad news.

First, the good news. The adult Japanese beetle, which feeds on about 300 plant species, has just about run its course. University of Kentucky Entomologist Lee Townsend said Kentuckians can expect the beetles to be active for another two to three weeks, although some may live into September.

“We should be beyond the real peak of activity at this point,” he said.

Now, the bad news. While these ravenous insects have been chomping away at Kentucky landscapes, the females also have been laying eggs in the soil. Those eggs will hatch over the next three weeks, and young beetle grubs will emerge.

“So what we’re looking at now is the potential for the white grub stage, or the immature stage, of the beetle to cause problems in our landscape turf,” Townsend said.

White grubs are one of the most destructive insect pests of turfgrasses. The turf is damaged when the grubs chew off the grass roots just below the soil surface, reducing the turf’s ability to take up water and nutrients and, therefore, withstand the stress of hot, dry weather. 

“And that can end up in brown spots and dead spots in the lawn, where turf just pulls right up like a loose carpet because there are no roots,” he said.

There are several species of white grubs that can cause this damage, but larvae of the Japanese beetle, as well as masked chafer, is most common in Kentucky. With the heavy infestation of Japanese beetles this year, the potential for heavy turf damage from white grubs should not be ignored, Townsend said.

“If the soils are really dry and we’re short on rainfall during most of August, a lot of those eggs will never hatch,” he said. “But if we continue with a pattern of rain in late July and early August, that can mean lots of eggs hatching and a high potential for grub damage in the turf.”

There are some things that can be done to prevent or minimize grub damage. Preventive treatments, such as imidacloprid and halofenozide, can provide excellent control of newly hatched white grubs when applied before they hatch. Such treatments are most suited for high-risk sites with a history of grub problems or where heavy beetle activity is noticed.

However, “they need to be put on about this time to be effective,” Townsend said.

Once the eggs have hatched and grubs are present – usually in August or September – there are products that can be applied for curative control. Two that are currently available are trichlorfon and carbaryl. Both the curative and preventive treatments are available at garden stores.

Although there are biological/microbial insecticides available, such as milky spore, they provide inconsistent grub control, Townsend said.

Beyond insecticide treatments, the very thing that creates the potential for a white grub problem also can help control it. 

“The rain that is going to help with egg hatch is also going to reduce moisture stress on the turf,” Townsend said. “Watering the turf can help pull it through if low-to-moderate numbers of grubs are there.”


Writer: Terri McLean 859-257-4736, ext. 276

Contact: Lee Townsend, 859-257-7455