How to manage grubs

The tipping point Ten or more grubs per square foot may indicate control is necessary. (Photo: Nufarm)

Grubs not only damage turf, they’re tasty to skunks and other nuisance animals. Aside from the stink, animals foraging for grubs attack plant root zones, causing even more damage to lawns. Because of those dual problems, pest control experts call grubs one of the most damaging creatures that lawn care operators (LCOs) regularly face.

“It is difficult for LCOs to forecast, however, whether a property will or will not have a grub infestation,” says Aaron Hathaway, technical services manager for Nufarm. “Keep tabs on the history of grub damage at each property as beetles may lay eggs from year to year in the same areas. It is also worth taking a quick look within the soil during peak grub feeding, typically in August or September, in lawns that haven’t been treated by digging up a Frisbee-sized area and counting the grubs seen just underneath the sod.”

And then what? Hathaway says the grub count test should guide LCOs on pest control.

“Just because grubs may be present doesn’t mean that control is necessary. A threshold of more than 10 grubs per square foot is a good rule of thumb to warrant control measures,” Hathaway says. “A healthy lawn can maintain health with minimal populations. This attention to detail can bolster the relationship with a client and help turf managers become more familiar with different lawns and make better decisions based on real observations in the future.”

Best control practices

Rakim Turnipseed, Ph.D., product development manager, insecticides, at FMC, says there are some basic steps LCOs should take to prevent and control grubs.

• Maintain a healthy lawn with proper fertilization, mowing and watering to create turfgrass tough enough to withstand some pests.
• Identify the type of grub present. This step is vital to proper treatment. Grubs are beetle larvae. Identify the most common pest populations in your area to determine whether the grubs are from Japanese beetle, European or masked chafer, Oriental beetle or other beetle varieties. Knowing the grub type will tell you which insecticide to use and what watering methods will move the active ingredients into the soil.
• Apply treatments at the appropriate time based on whether it is a curative or preventive product. Some products that work as preventive treatments need to be applied earlier in the season.

“Unfortunately, treatments that don’t work well curatively are often made too late in the season after grubs have grown too large,” Turnipseed says. “And, sometimes LCOs fail to water in insecticides immediately after application.”

Common mistakes

Nufarm’s Hathaway lists common errors LCOs make when controlling grubs, agreeing with Turnipseed that timing is critical.

Not having preventive products down early enough in the season is a common mistake, he says. Preventive products depend on having insecticide in place before or just at peak egg laying.

This approach is preferred to curative methods, experts say. The more targeted applications lower insecticide use because the degradation time from application to grub ingest shrinks.

Hathaway says not watering in insecticide applications is another common misstep. The target for preventive applications is the soil where they can be absorbed by turfgrass plants and subsequently be fed upon by grubs. That’s why they must be watered in. On turfgrass leaves, active ingredients can be mowed off or broken down by sunlight.