This is the time of year to apply insecticides to control black turfgrass ataenius, Ataenius spretulus. Black turfgrass ataenius is a white grub that attacks highly maintained turf, such as that on golf courses. It is rare to find this insect in high enough numbers to damage lawns.

Black turfgrass ataenius overwinters as an adult in leaf litter and other debris in damp, wooded areas. Many golf courses have this type of habitat between fairways. In the spring, the adults migrate to highly maintained, well-watered turf to tunnel into the soil to lay their eggs. At this time, they are noticeable in the clippings baskets of greens mowers. These adult beetles are cylindrical, black, and about 1/4 inch long.

The resulting larvae are similar to other turf-feeding white grubs, being white, C-shaped, soft-bodied, and elongated, with three pairs of legs. The posterior end of the body ends in two large lobes rather than having a raster pattern of light spines as do other white grubs. Ataenius grubs appear slender or less robust than other white grubs and grow to only about 1/4 inch long.

This first generation matures in late June or early July, causing typical white grub-feeding damage to turf. The turf wilts and turns brown due to the grubs’ eating the roots. This damage allows the turf to be easily pulled up, where the white grubs can be easily seen in the root zone. In dry soil, the grubs may be several inches deeper in the soil.

The larvae pupate and emerge as adults in midsummer to lay eggs for a second generation. The second generation of grubs is present during August and September, as are the larger turf-feeding grubs such as masked chafer and Japanese beetle. This second generation pupates and emerges in the fall as black beetles that fly to wooded areas to overwinter.

Infestations of 50 black turfgrass ataenius or more per square foot of turf are usually high enough to cause turf damage. There are several insecticides that are effective against the grubs. Golf-course superintendents find that imidacloprid (Merit) or halofeno-zide (Mach 2) applied in the spring when Vanhoutte spirea, Spiraea x vanhouttei, is in bloom is effective for the entire season. Even though this shrub is now finishing bloom, it is not too late to obtain control and avoid damage. These insecticides usually control the first generation and stay active to control the second generation, as well as the larger turf-feeding grubs in late summer. One should cut through and pull up some turf in early August to verify that the insecticide has provided control on these later grubs. An alternative is to apply trichlorfon (Dylox) when grubs are present both in the spring and again in August. Dylox is short-lived, so be sure grubs are present when this insecticide is applied.