Black Turfgrass Ataenius

The adult black turfgrass ataenius beetle is 0.2 inch (5 mm) long, shining jet black, and has parallel grooves on the wing covers (elytra). Adults can be seen any time of day, especially on golf course greens and tees. Adult black turfgrass ataenius can easily be mistaken for another beetle, Aphodius lividus (not known to damage turf), which is slightly smaller and chocolate brown with straw-colored stripes near the center of the back and along the margin of the elytra.

Female ataenius adults burrow into the thatch and upper soil where they lay clutches of 11 or 12 eggs. Eggs hatch into scarab grubs, which can be distinguished from other white grubs by their small size, the scattered pattern of bristles on the last abdominal segment, and a pair of pads at the tip of the abdomen. At least two or three generations develop in California each year with up to five in the warmest part of the state. Adults are continuously active during warm months in inland areas. They probably overwinter in a reproductive dormancy.

Although black turfgrass ataenius is common in many turfgrass areas, it is predominantly a pest of golf courses, especially during summer on highly stressed, cool-season grasses. It is also commonly found damaging bentgrass-rye mixtures and in annual bluegrass.

The larval stage damages turfgrass by feeding on roots, resulting in irregular dead patches. The damaged area appears to be drought stressed, even where there is sufficient irrigation. Symptoms may resemble those of turfgrass root diseases such as summer patch, take-all patch, and Pythium root rot. Extensive root feeding sometimes allows the turf to be rolled back like a carpet. Digging by vertebrate predators, such as crows, raccoons, and skunks, is a common indication of high grub populations.

Turfgrass can be managed to withstand low levels of black turfgrass ataenius by carefully scheduling irrigations and modifying mowing practices. If sampling indicates the population requires treatment, several treatment choices are available, including the use of parasitic nematodes.

Milky spore (Paenibacillus spp.) organisms have been detected infecting black turfgrass ataenius in California. Milky spore pathogens affecting ataenius do not include the one that controls Japanese beetles and are not commercially available. When black turfgrass ataenius is infected with milky spore diseases in other geographical areas, it undergoes a 3- or 4-year boom-and-bust cycle at a site, then the site becomes protected for several years from further damaging populations because of the milky spores presence in the soil, but this has not yet occurred in California. For short-term control, the pathogenic nematodes Steinernema carpocapsae and Heterorhabditis bacteriophora are often effective.

Improve root development as much as possible to allow turfgrass to withstand grub feeding by following recommended irrigation practices based on evapotranspiration needs of turfgrass, using small-tine or water injection aeration, and raising mowing height as feasible.

The most effective insecticides, the neonicotinoids such as imidacloprid, provide best control if applied to just before adults lay eggs, generally before serious damage is seen. However, damaging infestations are not common and treatment is not regularly required, so this preventive approach is not recommended where an infestation is not expected. These materials can also be effective against very young grubs.

If irregular dead spots appear in turfgrass, sample for black turfgrass ataenius grubs or other insects. You can also sample about 2 weeks after adults are caught in black light traps. Use a cup cutter to sample for grubs underneath areas of turfgrass damage and in areas where grubs have been active in the past or are likely to occur (collars, wet spots, black layer spots). Grubs will be present at the thatch/soil interface. If there are more than four grubs per cup cutter sample (or 40 grubs per square foot), treatment is necessary. Threshold levels are much lower for bentgrass grown in the desert region than the rest of the state because of the heat and drought stress. Apply liquid sprays or nematode applications to moist turfgrass and granules to dry turfgrass. Irrigate following application to move the material into the zone of larval feeding.