Golfdom, December 2011

Continued on page 34 www turfgrasstrends com December 2011 TURFGRASS TRENDS 33 pathogens predators parasites residing in the golf course environment and if so whether the natural enemies could be isolated and applied as biological control agents In 2005 entomopathogenic nematodes EPNs were found infecting ABW larvae and pupae on several fairways in a statewide survey of New Jersey golf courses EPNs are microscopic insect parasitic roundworms that have an infective juvenile IJ stage capable of locating and infecting soil dwelling insects Further studies conducted on three golf courses in New Jersey indicated that two species Steinernema carpocapsae Sc and Heterorhabditis bacteriophora Hb regularly infect ABW larvae in golf course fairways and can reduce a single weevil generation by up to 50 percent The objective of this study was to determine if EPNs could be applied to turf to reduce ABW densities below damaging levels We screened commercially available species in the laboratory against different ABW stages and followed these studies with multiple field trials to assess their efficacy under field conditions Laboratory screening Five commercial EPN strains supplied by Becker Underwood Sussex UK Sc Steinernema kraussei Sk S feltiae Sf Hb and Heterorhabditis megidis Hm and two native strains Sc PB and Hb PB isolated from infected ABW larvae and pupae found in fairways were tested in laboratory trials Adult susceptibility to EPNs was low to moderate 11 65 percent mortality even under optimal laboratory conditions and at a high EPN rate Therefore EPNs do not show promise for the preventive control of ABW However larvae were moderately to highly susceptible to EPN infection with fourth instars tending to be more susceptible than fifth instars Despite high ABW densities in the laboratory trials 80 ft2 high control rates of fourth instars were observed for the commercial strains of Sf 89 percent and Sc 81 percent with somewhat lower rates for Sk 72 percent and Hm 69 percent Native and commercial nematode strains did not differ significantly in virulence to any ABW stage tested These observations suggest that EPN field applications should be targeted against the early fourth instars to maximize control rates and minimize the potential for turf damage Field trials Field trials were conducted in 5x6 foot 278 square meter plots on golf course fairways arranged parallel to the edge of the rough fairway border Application times were based on peaks in larval densities estimated by weekly core sampling in adjacent plots and timed to target the larval population entering the soil early peak in fourth instars Nematodes either reared in the laboratory native strains or formulated commercial product were suspended in water and applied with watering cans followed by a rinse for a total of 0125 in 31 mm of irrigation In 2006 high levels of ABW control 63 94 percent were observed with rates of 1 billion IJs acre standard EPN field rates to moderate ABW infestations 25 ft2 Sf provided the greatest control 94 percent but was not statistically different from the other treatments Figure 1 The 2007 field trials included an additional commercial strain Hb and two application rates 1 and 05 billion IJs ac for each species Trials were conducted on fairways where the larval densities in the untreated control plots 65 larvae per square foot exceeded commonly accepted thresholds for damage 40 larvae per square foot Though higher EPN application rates led to greater control Two species of entomopathogenic nematodes infect annual bluegrass weevil larvae in fairways and can reduce a weevil generation by 50 percent PHOTOS COURTESY BEN MCGRAW PH D