Taking an environmentally sensitive approach to pest management
In the past, zoysiagrass was deemed a “no to low-maintenance” turf for lawn use, but an emerging insect pest may be changing that notion. Over the last two weeks, billbug grubs have been observed in declining zoysiagrass and bermudagrass samples of lawns and athletic fields. Infested areas are patchy and appear to be impacted by our current drought situation, yet supplemental irrigation is not keeping these areas healthy. Numerous small billbug grubs were observed throughout the thatch and soil profile of these samples, and the feeding of the grubs and adults is the true cause of turf decline. Sample locations include St. Louis, Rolla, and Columbia, so the problem appears to be widespread throughout the eastern and middle part of the state.
There are four billbug species that affect turfgrasses: bluegrass, Denver, Phoenician, and hunting. The bluegrass billbug is well established in the Midwest and northern states, and is one of the top three pests of Kentucky bluegrass. Denver and the Phoenician billbug, as the names imply, are not located in this region and are limited to western states. This leaves the hunting billbug, a species thought to reside primarily in the Southeast. Because most of these finds have been in warm season turf species, I suspect most, if not all, of these recent samples have been larvae of hunting billbugs… and this is not great news. Additionally, we have had captures of hunting billbug adults from zoysia plots at the University of Missouri Research Farm, confirming the insect species. Evidently, we really are officially part of the SEC!
The hunting billbug (Sphenophorus spp.) is primarily a pest of zoysiagrass and bermudagrass, but may also feed on Kentucky bluegrass and field crops such as corn and wheat. Adults are ~ ½” long, black to dark reddish brown, have a pronounced curved snout (the bill), and reside in the thatch layer. Larvae (grubs) are very small, 1/8 –3/8“ long, and unlike annual white grubs have no legs.
Research is still ongoing to determine the complete life cycle, but it’s thought the billbug survives as a dormant adult during the winter and emerges in early spring. It begins to feed and lay eggs in mid-late spring in the leaf sheath. Eggs hatch in 3-10 days and the small larvae start to feed inside the leaf stem and migrate down into stolons. The larvae soon outgrow the stems and fall out into the thatch layer where they continue to eat stolons and roots. After several weeks of feeding, the larvae dig 2-4” into the soil and pupate into new billbug adults. In our region, we can expect two generations of the billbug, and judging from the size of recent finds the larvae are diving down in the soil to pupate. Since another generation is coming, control of active infestations now is crucial to limiting further damage later this summer and fall.
Billbug damage may be the most often misdiagnosed problem in warm- season turfgrass, appearing similar to damage from diseases, drought, chinch bugs or delayed spring greening. The adults are reclusive, only come out at night, and are well camouflaged. Also, for a good portion of their larval stage, the billbug grub is inside the plant, making detection difficult. Oftentimes, the only diagnostic symptom of billbug damage is the hollowed out stolons and leaf stems apparent after the larvae emerge from their turfgrass hatchery and feeding chamber. Many declining zoysia lawns were reported in eastern MO this past spring, and residual or early spring billbug activity may have been a factor in these cases. Current low soil moisture levels are making billbug damage more apparent than in previous seasons.
Now is the time for billbug scouting as all life stages may be active, and larger grubs are emerging from the plant. In zoysia and bermudagrass turf areas that are not responding to irrigation, break out the shovel. Dig out a 3-4 inch square of turf and break it apart, sifting through the top 1-2 inches of soil and thatch. The small white grubs should be apparent in the next week or two, but their time is fleeting. Another way of monitoring is to target the adults with pitfall traps. Using a small plastic cup or similar, dig out a few areas in the area and place the cup inside with the lip just even with the soil surface. As the adult billbugs crawl around at night, they will fall into the cup and can be observed. Another good use of the “red solo cup”.
The species and cultivar of zoysia most often grown in Missouri (Zoysia japonica cv. ‘Meyer’) also happens to be the most susceptible to billbug damage. Other cultivars of Zoysia japonica are also susceptible, so renovating to another cultivar within this species may not reduce damage. Zoysia matrella is a more resistant zoysia species to billbug, but is not as cold tolerant as Z. japonica and not widely available in this region.
Biocontrol products containing the entomopathogenic nematodes Steinernema and Heterorhabiditis have been found effective in controlling larvae and adults. Spraying 1 billion infective juveniles/acre is necessary for control and should be applied at the first sign of billbug presence or damage. If these biocontrols are attempted, it is crucial to pay attention to the expiration date, application, and storage instructions to maintain viability of the living organisms within the jug and spray tank.
If billbug larvae or adults are found and associated with declining turf, an insecticide treatment is often necessary. For adult control in early spring, bifenthrin (Talstar), deltamethrin (Deltagard), imidacloprid (Merit), or lambda-cyhalothrin (Scimitar or Battle) are recommended. Adult control is often a preventive measure in areas that have a perennial billbug problem. For larvae control, clothianidin (Arena) or thiamethoxam (Meridian) is suggested. If both larvae and adult control are necessary however, (like NOW) applications of chlorantraniliprole (Acelepryn), or the combination products clothianidin + bifenthrin (Aloft), or imidacloprid + bifenthrin (Allectus) are needed. To target billbug larvae, it is crucial to water in the insecticide with 1/8 - ¼ inch of irrigation.
The Entomology team at North Carolina State University led by Dr. Rick Brandenburg is currently conducting research on billbug biology and control. Other online resources for billbug biology and control information are listed below:
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REVISED: July 28, 2016