FEATURES
The Control Center
Black Turfgrass Ataenius

by John C. Fech and Frederick P. Baxendale

Gray leaf spot is a fungal disease that causes lots of damage to golf course fairways, but you don’t hear too much about injury to home lawns. In the insect world, the black turfgrass ataenius (BTA) follows a similar pattern.

Description

All white grubs are similar in appearance with cream-colored, C-shaped bodies, reddish-brown heads and three pairs of short legs located immediately behind the head. When fully developed, they range from .25 to over 1.5 inches in length, depending on the species.

Sampling for white grubs. Photo by Tom Eickhoff, UNL.

Identifying the different white grub species is best accomplished by examining the arrangement of hairs and spines on the raster area, which is located on the underside of the terminal abdominal segment. These patterns can be readily distinguished using a 10X hand lens. Black turfgrass ataenius grubs can be is distinguished by their small size (only about .25 inch long when fully grown) and the presence of pad-like structures at the end of the abdomen.

When identifying white grubs, or any small insect for that matter, it helps to have a vivid imagination. Like searching the sky for various constellations, seeing all of the characteristic features can be difficult. The rastral pattern of black turfgrass ataenius grubs could also be described as a sideways capital letter B next to the anal slit or side-by-side rolling hills. Whichever you use to characterize the feature, they are surrounded by a random pattern of hairs. It’s always helpful to examine several insects to be sure of your identification.

BTA life cycle

Black turfgrass ataenius overwinter as adults (beetles) in loose soil, pine needles and leaf litter. The dark brown to black .25-inch-long beetles begin moving back into turfgrass in March or April. In most regions of the U.S., there are two generations per year. Overwintered females deposit eggs in soil and thatch. Upon hatching, the larvae feed on grass roots for three to five weeks before pupating. Most first-generation adults emerge in mid-July. Second generation larvae begin to feed on grass roots in late July or early August and mature into the overwintering adults by October.

Preferred hosts

Damage by black turfgrass ataenius has primarily occurred on golf course fairways in the Northeast. Greens, tees and fairways seem to be the favored feeding sites for black turfgrass ataenius grubs. In temperate regions, larvae damage the roots of annual bluegrass, creeping bentgrass and Kentucky bluegrass. In more southern areas, where warm-season grasses predominate, these grubs can also be occasional pests on bentgrass greens.

Treatment thresholds

While black turfgrass ataenius larvae closely resemble other species of white grubs, they are much smaller, averaging only about .25 inch in length. Accordingly, larger numbers of grubs must be present and actively feeding before turf injury occurs. Most grub species begin damaging turf when they reach five to 10 per square foot. Because of their size, treatment thresholds for black turfgrass ataenius range from 25 to 40 per square foot. In addition to grub numbers, the time of year must be considered when making a treatment decision. Turf may not be damaged by the first generation, as springtime weather conditions usually promote vigorous growth of shoots and roots. However, during second-generation feeding, warmer and drier weather is commonly present, creating increased stress on turf plants. In addition, root damage in summer is more consequential, as the rooting for cool-season grasses is at its shortest depth for the year. When root growth slows down in summer, the plants are slow to respond positively to root feeding. Other important factors to consider when making a treatment decision include previous feeding injury, the history of the site, the height of cut of the turf, irrigation scheduling and the growth rate of the turf species and cultivar.

Sampling with a cup cutter. Photo by Tom Eickhoff, UNL. Black turfgrass ataenius adult. Photo by Frederick P. Baxendale.

Monitoring and scouting

To determine if black turfgrass ataenius larvae are present in your turf, focus on the feeding zone. Similar to other white grub species, the feeding zone for black turfgrass ataenius is generally at or near the turf/thatch interface. Occasionally, feeding will occur at lower depths, depending on the turf stand.

Fortunately, the tools needed to inspect your turf are readily accessible and inexpensive: a shovel, garden trowel or cup cutter. To confirm the presence of grubs, cut 6-by-6-inch sections of turf on three sides, peel back the sod and examine the upper 2 inches of the rootzone for the presence of pests. A cup cutter can also be used to sample for black turfgrass ataenius and other soil-inhabiting insects by taking 4-inch-diameter soil cores.

Enough samples should be taken to assure a reasonably accurate estimate of pest numbers in the sampled area. If turf damage is evident, but no pests are detected, examine the turf for other causes of injury such as disease, excessive thatch, improper mowing, heat or moisture stress. Overall, use your knowledge of the insect’s life cycle and the previous history of the site to guide the timing of the monitoring process. Ideally, grubs should be found before injury occurs, soon after hatching. Scouting on a regular basis provides the best results.

Black turfgrass ataenius overwinter as adults in loose soil, pine needles and leaf litter. Photo by John Fech, UNL.

Control

For all white grub species, including black turfgrass ataenius, control is largely an issue of getting the treatment material to the area of active feeding. Most of the preventively applied insecticides, including chlorantraniliprole (Acelepryn), clothianidin (Arena), imidacloprid (Merit) and Thiamethoxam (Meridian), are systemic in nature and will be taken up by the plant and translocated to the rootzone where the grubs are feeding. Curative insecticides, such as carbaryl (Sevin) or trichlorfon (Dylox), must be watered in for acceptable control. To be successful with these products, aerate the affected area before treatment, mix the insecticide according to label directions, make the application and apply .5 inch of posttreatment irrigation. If conditions have been hot and dry and grubs are deeper in the soil, a pretreatment irrigation of .5 inch applied 48 hours before the insecticide application should encourage grubs to move closer to the soil surface and enhance the level of white grub control.

John C. Fech is a horticulturist, certified arborist and frequent contributor located in Omaha, Neb. Frederick P. Baxendale is a professor and extension entomologist with the University of Nebraska-Lincoln.