Black turfgrass ataenius first-generation larvae are nearing full size across Illinois. If they have not been scouted, with high populations being treated, damage is likely to appear on the tees and greens of golf courses by early July.
Black turfgrass ataenius is a small, white grub that overwinters as an adult beetle in moist, fallen leaves and similar protected locations. In the spring, typically as Vanhoutte spirea is blooming, the 1/4-inch long, cylindrical, black beetles fly to golf courses to lay their eggs. They are found in the clippings baskets of greens mowers at that time. Eggs are laid over the next couple of weeks, with egg hatch occurring a couple of weeks later.
The larvae are similar in appearance to other white grubs, being white and C-shaped, with legs and brown heads. However, they are much smaller than other white grubs, being only about 1/4 inch long when full-grown. Rather than a raster pattern on the underside of the last abdominal segment, they have two large pads. Because they are smaller, each grub does not eat as much root tissue as larger species, so higher grub numbers are required to cause injury. Cut through the sod and pull it back to scout for grubs in the root system. The damage threshold for black turfgrass ataenius is 50 per square foot, as compared to 10 to 12 for the larger species of white grubs. In heavy infestations, 150 to 300 black turfgrass ataenius grubs per square foot is common. Over 1,000 grubs per square foot have been found.
Damage is similar to that of other white grubs. Because the roots are eaten off the grass plants, the blades wilt and turn brown. Where there are high numbers of these grubs, roundish brown areas of turf become evident. Heavily damaged turf peels back like a carpet from the soil because there are few roots left to keep it attached.
Mature larvae pupate in July and emerge as adults for a second generation. This second generation is in the larval stage when the larger white grubs such as Japanese beetle and masked chafers (annual white grubs) are present. However, black turfgrass ataenius larvae develop fully in the fall, pupate, and emerge as adults. These adults fly to overwintering sites. Many golf courses contain ideal sites, typically with a screen of trees between adjacent fairways. The fairways are built up, which allows water to run off into these forested, interfairway areas, creating ideal, moist leaf litter for the adult beetles to overwinter. Also, they are close to the fairways, tees, and greens in the spring.
Larval damage is most likely in the wettest areas of turf. On a golf course, larval numbers are heaviest in swales on fairways and areas around greens where water drains off and tends to puddle. Larvae are probably common on tees and greens because they are watered more frequently than other locations.
Typically, damage occurs on highly maintained turf, making this mainly a golf course pest. Although home lawns commonly have a small number of larvae, damaging numbers are found on highly maintained lawns that are heavily fertilized, irrigated, and mowed frequently. In these situations, damage typically occurs in a swale, where water collects.
Black turfgrass ataenius is a scarab beetle, as are all white grub species. Scarabs are a large family of beetles in which most of the species are scavengers. They include the dung beetles, which feed on manure, and other species that are found in rotting wood, where they probably feed on the wood rot fungi. It is thought that black turfgrass ataenius may be attracted to highly maintained turf because high fertilization results in heavy growth, with more thatch, clippings, and other decaying plant material. Irrigation levels associated with highly maintained turfgrass provides the moist conditions that also attract this insect.
Management involves the application of imidacloprid (Merit) or halofenozide (Mach 2) in the spring about 2 weeks after high beetle numbers are found in clippings baskets. Merit and Mach 2 are long-lasting insecticides that should last long enough from the spring application to provide control on the second generation of black turfgrass ataenius and the larger white grubs in August. However, scouting is recommended in the first half of August to be sure that these grubs are being controlled. Damaging infestations of black turfgrass ataenius larvae can be treated with trichlorfon (Dylox). Dylox kills the grubs within 3 days, rather than the 3 weeks it takes for Merit and Mach 2. The insecticidal nematode, Heterorhabditis bacteriophora (Hb nematode), is also effective against the larval stage.