The when, where and how to control this pest
Grub control is one of the trickier aspects of turfgrass pest management. The different types of grubs that cause damage, confusion over life cycle progression and the fact that actually seeing the grubs usually requires digging into the soil, all add up to one giant challenge for turfgrass managers.
One of the most important things to remember is that not all chemical products designed to control grubs will work at all times. “Timing and use of the appropriate product are both critical with grub control,” says Terry Davis with Michigan State University’s department of entomology. He points out that mistakes are commonplace when it comes to both factors.
The first key is to distinguish between preventive and curative treatments, the latter being what is needed during the late fall or early spring for active grubs. “There are two products that you can use as a curative if you find active grubs. Those are trichlorfon or carbaryl. It’s critical to put these products out when they’re active. If you put them out in July, it’s not going to do anything,” Davis explains.
In his part of the country, at least, the correct timing for fall treatment with these products ranges from around Labor Day until there is no longer grub activity up near the surface (check with your extension office if you have questions regarding timing in your region). “If it’s European chafer in home lawns, that could be as late as mid-December,” Davis says. While treatment can take place throughout the fall and early winter months, he says that, “You’ll see a lot more kill, and quicker kill, when it’s warmer.”
European chafer will start earlier and feed later than Japanese beetle, Davis adds. European chafer also tends to prefer nonirrigated turf. “Japanese beetles prefer moist turf. You will find it in nonirrigated turf, but rarely at numbers that will cause damage,” he adds.
Davis says both products call for fairly high rates, and he discourages skimping on the rate. “It’s just difficult to get chemical down to where the grubs are,” he says. “Don’t expect immediate results, it could take a few weeks.” He points out that one homeowner product is marketed as “24-hour grub control,” which causes confusion. “That’s just not going to happen. Maybe at 10 days you’ll start to see that they’re not moving around as much, but they’re not going to be gone for three weeks or so.”
Davis says that, prior to treating for grubs, it’s important to determine what the grub population actually is. “If you’re going to apply a curative compound, it’s wise to know first that you actually have a problem,” he says. That’s sometimes easier said than done, however. “It’s interesting, because you can find a fairly serious grub problem and rarely see any adults, because European chafer flies right after dark. Usually, if you go out in late June right at dusk, as the sun is setting, you’ll be able to see European chafer come up out of the turf, hover for an instant, and then fly up and congregate in trees. If you see lots of insects buzzing around in trees, that’s an indication that you need to be concerned about possible grub damage to the turf. Japanese beetle is pretty obvious, because you’ll see them all over any roses or lindens in July. That’s a little bit of an indication of how bad the problem is.”
Eggs are laid in midsummer and develop into full-size grubs in the fall. “You can see them after Labor Day, they’re very obvious at that point,” says Davis. At that point, the grubs will be within the top 2.5 to 3 inches in the rootzone. “If you’re going to use a curative product, you need to look in a lot of locations,” he explains. “You can just take a shovel and dig up 1 square foot. We recommend that you can have up to five grubs per-square-foot in non-irrigated turf without having damage. If you have irrigated turf, you can actually tolerate up to 15 grubs per square foot. Of course, I’d be getting pretty nervous at that point.”
Davis says it’s not only those new to turfgrass management who make mistakes regarding the timing and choice of grub control products. “For example, I recently saw a situation where a chemical company representative recommended to a golf course that they apply Meridian for an active grub [European chafer] problem in the spring,” he recalls. “The application went on in late April/early May. What was put out would have no impact on the grubs that were in the ground, because they were too big.”
To make matters worse, because the golf course was concerned about cost, the representative recommended they apply on the low range of the label rate. So, there’s less chance that the chemical application—applied many months too early—will provide a carryover effect to the fall on new grubs. “It was a very serious problem, and a sad case,” says Davis of the level of turf damage that occurred because of the improper application.
In warmer weather states, grub control timing can be even trickier. In Florida, there may be more than one generation of white grubs in a year, explains Dr. Eileen Buss, associate professor and extension specialist with the University of Florida/IFAS entomology and nematology department. “For masked chafer in turf, damage starts showing up in late July and early August, with the second generation adults out in September and October. I don’t generally recommend applying control for them, because they don’t tend to cause too much damage during the winter. Most of the turf damage we see then is caused by the sugarcane beetle. They can cause a lot of damage starting in late September and early October, all the way through January.” August and September provide the best curative treatment opportunities for this large, destructive species, she says.
When grub damage is noted and curative applications are needed, Buss says that, “the second instars are easier to control than the third instars, so it’s better to get them earlier before they cause too much damage.” In Florida, where there are multiple grub species that can cause turfgrass damage, it’s necessary to first determine the species responsible and the number of grubs present.
“I always recommend scouting, but hardly anybody does it,” says Buss, noting that many pest control operators are only on a specific lawn every few months, making regular scouting difficult. “They have to make decisions very quickly, and it’s difficult for technicians out on the job to monitor. Most of them don’t.” For those willing to make the commitment to monitoring, Buss says the grubs can be found up in the thatch and down to about 3 inches deep in the fall.
She says it’s difficult to pinpoint when treatment is needed based a specific number of grubs per square foot, but that the turf will be more susceptible to damage if it’s under any stress, such as drought or nutrient stress. “Even compaction can lead to increased damage,” Buss adds.
“Dylox (trichlorfon) is one of the only remaining curative products on the market. Sevin (carbaryl) is also considered a curative product, but it probably is less efficacious. Both of them break down quickly, so reapplication is sometimes necessary,” Buss explains. With such limited curative options left on the market, and no new options recently introduced, Buss recommends treating preventively.
Michigan State’s Terry Davis agrees that preventive treatments are typically more effective than curative treatments in controlling grubs. “Normally, with a curative treatment, you’re going to get 65 to 70 percent control. With a preventive treatment, you can get 95 to 100 percent,” he explains. That doesn’t mean you should wait until next spring to treat. For those who use scouting and find high grub populations, applying a fall curative treatment will control populations now and, by reducing the number of grubs in the ground, will also lessen turf damage next spring. Just be sure you’re using a curative, rather than preventive, product, and that the timing is appropriate.
“Another tricky thing for turfgrass managers is knowing when to stop treating for grubs,” says Davis. “If you’ve applied a preventive compound for the last four years, it’s maybe worthwhile backing off on part of a yard and then monitoring it to see what happens. Then, keep some curative compound on hand if there is a problem, or pay attention to what’s going on nearby. If there’s a neighboring yard that doesn’t have a lawn service that treats for grubs, see if they have damage. Monitoring is time-consuming, and it’s a little messy because you have to dig, but it’s very worthwhile because you can save money for your customers, and they’re going to like that.”
Patrick White is a freelance writer and editor who has covered every aspect of the green industry in the past 13 years. He is based in Middlesex, Vt., and is always on the lookout for unusual stories.