In much of the country, just before spring starts, the blanket of beautiful white snow starts melting away and the grass starts growing again. But there are things slumbering beneath the snow waiting to attack that green grass just a few weeks after it appears. We’re talking about spring pests, of course.
White grubs are the larval stage of certain species of beetles, C-shaped and soft-bodied with chestnut-colored heads and three pairs of legs. Size varies according to stage of development and species, but the most mature ones range from ¼ to 1½ inches long. Some grubs take two or three years underground to grow and develop, overwintering just below the frost line, waiting for the right time to pupate.
“Grub” is a good term for these larvae. Their main job is finding grub, i.e., the tender roots of grass plants, which are especially vulnerable during a spring green-up. Their voracious appetite for your clients’ turf is what makes them so destructive.
White grubs are found pretty much everywhere in the continental U.S. Some of the most common white grubs are the larvae of masked chafer beetles, Japanese beetles, May beetles, black turfgrass ataenius beetles and green June beetles (often confused with Japanese beetles because of their close resemblance). The adult female beetles lay eggs, and when the larvae hatch, they journey through various instars (stages), pupate and finally emerge from the ground as adult beetles who then mate, lay eggs and start the cycle all over again.
Billbugs are another major turf pest. Their larvae look very similar to white grubs but are legless, with cream-colored bodies and dark brown heads. They damage both warm- and cool-season grasses by feeding on or inside the stems, crowns, roots, stolons and rhizomes.
Other bugs attack turf too. “Some of the caterpillars, like sod webworms, their mature larvae will start feeding again in the spring and cause damage,” says Doug Richmond, PhD, associate professor of turfgrass entomology and applied ecology at Purdue University, West Lafayette, Indiana. “Brown cutworms continue feeding under the cover of snow and surprise people in the spring when all of a sudden the turf doesn’t green up.”
A lawn shows signs that something is wrong: thinning turf, dead areas, brown spots. But these could mean a lot of things besides bugs chewing on the roots. “The first thing I look for is turf going off-color like it’s going through drought, maybe starting to turn yellow,” says Robert Avenius, north central region technical manager for TruGreen, Memphis, Tennessee. To make sure grubs are the cause, he does the “tug test.” Grab a hunk of grass and give it a firm but light yank. If a section starts to pull up easily like untacked carpet, you know the root system has been chewed away by grubs. You will probably be able to see the culprits lying there just below the surface.
A lawn full of dug-up spots is another clue. “Those are telltale signs of animals digging for grubs: raccoons, skunks, armadillos, depending on where you are in the country,” says Richmond.
“You’ll see almost comical little nose prints on the ground from skunks sniffing for grubs,” says Nicole Hendrickson, a sales representative at Advanced Turf Solutions, Fishers, Indiana, and vice president of the Midwest Regional Turf Foundation. “By the time that happens, you’ve got a bad infestation issue.”
The next step is finding out just what pests the turf is infested with. “There are a lot of look-alikes for these pests,” says Ricardo A. Ramirez, PhD, associate professor and entomologist, department of biology, Utah State University in Logan. He offers this example. “At a golf course where I was trapping beetles, the superintendent came over and said, ‘We’ve been getting a lot of Japanese beetles here.’ This surprised me, because there are very few in this part of Utah. He pulled a very shiny green beetle out of the trap to show me — but it was a predatory ground beetle (a beneficial insect that eats other insects and their larvae). He was confused because they also have shiny iridescent green bodies.”
To treat or not to treat
A client might notice a grub and call you to come spray. That doesn’t mean you should, however. “Just because there’s one grub in the lawn doesn’t mean you have to do something about it,” says Ramirez. “It’s only when you have a large population and the lawn is really starting to look terrible that you need to take action.”
Preventive spraying for common pests could actually cause more problems than solve them. “If you know that a property has a history with a certain pest, then a prophylactic spraying could be done,” says Hendrickson.
But don’t spray before you even know there’s a problem. “That’s a good way to encourage pesticide resistance,” says Rodriguez.
Turf can tolerate the presence of grubs up to a certain threshold number, and each species is different. You don’t need to treat until that threshold has been reached, says Richmond. If a lawn or field is green and vigorous, it can tolerate a much higher population. “You could have many more grubs in the ground before a problem becomes evident,” says Richmond. “But if the turf is poorly maintained, or the soil is compacted, that lowers the tolerable threshold.”
“Say you do a tug test, and it reveals five Japanese beetle grubs in about a 1-foot square,” continues Richmond. “Not a serious concern; I’ve seen as many as 20 Japanese beetle grubs per square foot where you would have never known anything was there. But in some parts of the country, they have European chafer, another white grub species. Once you get to the five grubs per square foot level with that insect, you’re less likely to be able to mask the damage just with proper management practices.”
A “float test” will tell you just how many grubs you have per square foot. Mix 2 to 4 tablespoons of liquid dish soap in 1 gallon of water. Mark off 1 square yard of lawn and sprinkle the solution evenly over the suspect area. Wait 10 minutes, then count the grubs that have come up.
When to treat
After you’ve determined that treatment is warranted, when should you do it? This will vary a bit depending on where you are. You don’t want to do it too early or too late. Timing this can be tricky for landscapers with hundreds of lawns to treat.
Many do it right around July 4. It should be done when the larvae are just starting to hatch out, whenever that is in your region, because they’re easier to kill at that stage. “When the larvae are small, you can control them very nicely,” says Avenius. “When they get bigger, to the size of a shrimp, they are a lot tougher to control. You’ll need a different insecticide and more of it.”
If the grub problem goes unnoticed until later in the year, even through August, it’s still possible to get it under control. “It will take longer, but you can still treat,” says Hendrickson. “There will be a mixed population at that point, some first instar grubs along with some third instars.”
Keeping the grubs away
Following the principles of integrated pest management can help keep a client’s turf from getting infested in the first place, says Ben Dasch, maintenance division director at Keane Landscaping, Wylie, Texas. The foundation of IPM is employing sound cultural practices that promote healthy, vigorous turf capable of tolerating or quickly recovering from insect damage, and every landscaper already knows what these are: proper fertilization, proper irrigation, removing excess thatch, aerating and cutting grass to the right height.
For example, a good cultural practice like cycle-and-soak watering can prevent Japanese beetle females from laying their eggs, which need water to hatch. But a soggy lawn is practically an engraved invitation.
IPM means dealing with pests as conservatively as possible, not routinely spraying before you even know if a problem exists. You only reach for the pesticides when there’s no other option. “The goal of IPM is not to eliminate insects, but to keep insect pests below damaging levels,” says Richmond.
Choosing the right variety of grass is also part of it. “The likelihood of or severity of insect damage can be reduced by picking turfgrass species that are well-adapted for that specific site,” says Richmond.
Some grass types, the endophyte-enhanced varieties, harbor a secret anti-bug weapon. An endophyte is a microscopic fungi found in many types of perennial rye, tall fescue and creeping red fescue. “The fungus produces a toxin that makes it unattractive to certain above-ground pests, especially billbugs, as a food source,” says Ramirez.
Dasch focuses on building up the strength of any lawn he inherits the care of, because he thinks it’s the best, least toxic and cheapest form of pest control. That is the essence of IPM. “And that’s the beauty of having a nice, healthy lawn,” he says. “It’ll defend itself just as a healthy human immune system fights off the germs it encounters on a daily basis. A lawn is going to function the same way, if it’s got nutrient-rich soil and its grass base is good and healthy.”
Where to get help
Your local university extension is a good place to get help with pest identification, treatment options and advice on best management practices. They’ll have the most up-to-date information about the pests found in your region.
We’ll never kill every last grub on the planet (nor would we want to). But with the right practices, we can keep their numbers way down and give our clients’ lawns, fields, courses and campuses a fighting chance.