Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.
Issue link: http://gcmdigital.gcsaa.org/i/706647
08.16 GOLF COURSE MANAGEMENT 65 Damage thresholds for billbug larvae vary widely from the eastern U.S. (30 to 80/square foot [0.09 square meter]) to the western U.S. (1 to 10/square foot) and are somewhat mis - leading because high densities may not cause significant damage where turf is healthy. Bill - bug thresholds are lower in the West because weather patterns create drier conditions in summer when drought stress limits turfgrass from tolerating, or outgrowing, feeding dam - age. Tolerance of imperfect turf on golf courses is usually low, so insecticides are a standard practice for managing billbugs where they are known to occur. Unfortunately, "damage thresholds" are often the result of later-instar larvae, which are in the crown or soil and therefore more difficult to control than young larvae recently hatched from the egg. Insecticide management strategies When using insecticides to control bill- bugs, superintendents should base the timing of applications on billbug biology. Insecticides may be applied in March or April to target adults as they emerge from overwintering sites into managed turf. To be successful, this ap - proach requires extensive monitoring (as men- tioned previously) and precise timing of con- tact insecticides to the infested turf. The most effective and most flexible treat - ments are thought to be preventive applica- tions of systemic insecticides for larvae in May or June. Systemic insecticides are distributed throughout the plant and generally have a longer period of effectiveness than surface- applied contact insecticides. Systemic insecti - cides are timed to target larvae that are newly hatched from the egg or first instars inside the plant. The active ingredient reaches young lar - vae inside the stem, but also persists in the root zone and soil and affects older larvae when they begin feeding on roots and crowns. For - aging adults may also feed and be exposed to systemic insecticides at this time. After damage is evident, curative applica - tions (or "rescue applications") can be made in July or August to target larger larvae in the thatch, crowns and soil. This timing is the least flexible and takes place when the damage often has already been done. A Purdue Exten - sion publication details more specifics for bill- bug control at these various timings, including available insecticide options (8). Because insecticide efficacy data has never been tested or reported in Utah, the objective of this work was to evaluate two newer insec - ticide options for controlling billbugs by com- paring them with a current standard product available for billbug control. Research In field research, finding natural popula- tions of turf pests with densities high enough to cause extensive and uniform damage is challenging. Tracking down a location with repeatable insect pressure over multiple years might be considered a miracle, but I was for - tunate enough to find such a place in northern Utah, where I conducted four insecticide ef - ficacy trials from 2013 to 2015. The bulk of the insecticide evaluations were based on pre - ventive applications in May, when adults were beginning to lay eggs and before larvae were present. Trials were conducted on a golf course fairway in 2013, 2014 and 2015, and on a lawn in 2013. Neonicotinoids (imidacloprid, thiameth - oxam, clothianidin) have been the industry standard for preventive applications that con - trol billbug larvae, but in some areas, neonic- otinoid use is restricted. Two new alternatives to neonicotinoids for billbug control are the anthranilic diamides Acelepryn (chlorantraniliprole, Syngenta) and Ference (cyantraniliprole, Syngenta). These products belong to a newly developed class of insecticides (IRAC Group 28), are sys - temic, and are taken up by the plant foliage and roots. These materials selectively activate insect ryanodine receptors, thereby causing mortality from the uncontrolled release of cal - cium ions in muscle cells, which causes paraly- sis. Acelepryn was registered for turf in 2008, and Ference was registered in 2014. General methods Adult activity was tracked each year with pitfall traps installed near each trial. This in - formation was useful for determining when to make applications that targeted the egg-laying stage, or when adult activity was increasing. Insecticide treatments were applied in May of each year with a backpack sprayer operat - ing at 40 psi (275.8 kPa) through a boom with four TeeJet AI11002VS nozzles delivering 2 gallons/1,000 square feet (87 gallons/acre; 814 liters/hectare). Treatments were applied to 4-foot-by-10-foot (1.2-meter-by-3-meter) plots arranged in a randomized complete block and replicated five times. Insecticide treatments were not watered in for at least 24 hours after application, providing time for translaminar uptake of insecticides to occur. Fairway turf was predominantly annual bluegrass (Poa annua L.) with some perennial ryegrass (Lolium perenne L.) and Kentucky bluegrass (P. pratensis L.) mowed at 0.6 inch (15 mm) three days each week. Fertility in - cluded 2 to 3 pounds of granular nitrogen per 1,000 square feet (9.76 to 14.65 grams/square meter) each year, and turf was irrigated each night to replace 70% of reference evapotrans - piration (ETo). The soil was sand (93% sand, 6% clay, 1% silt) with a pH of 7.6 to 8.2, 1% to 4% organic matter, and minimal thatch (<¼ inch [6 mm]). Billbug control was measured by larval counts and visual damage estimates. Larvae were counted in July (multiple times in 2013 and 2014, and a single assessment in 2015) from three to five 3.5-inch-diameter (9-cm- diameter) cup cutter plugs (depending on trial and year) pulled from each plot. The number of larvae per sampled area was converted to number per square foot for standardization across trials and years. Calculations that com - pared larval means of treated turf with those of untreated turf were done to determine per - cent control. Turf damage was visually rated on a scale of 0% to 100% in June, July and August each year. Turf quality was also rated using a 1-9 scale, where 9 is the best, 6 is acceptable, and 1 is dead turf. Phytotoxicity was also monitored after each application. 2013 methods and results Met ods specific to 2013 trials The first year of testing began with three major questions: What species of billbugs are in Utah? What kind of population densities are present? Are there multiple generations of billbugs? Therefore, two identical trials were conducted — one at the golf course, and an - other on a nearby lawn with a history of bill- bug damage. The lawn differed from the golf course site in several respects. The lawn was Kentucky bluegrass mowed at 3 inches (76 mm) only once each week; it received less fer - tilizer (1 to 2 pounds nitrogen/1,000 square feet/year [4.88 to 9.76 grams/square meter/ year]) and less irrigation (70% ETo replaced every 3 to 4 days); and the soil was silt loam (37% sand, 26% clay, 36% silt) with more thatch (¾ inch to 1 inch [19 to 25 mm]). Without having a clear understanding of billbug biology for the region, two application