ECOLOGY AND MANAGEMENT OF GRASSHOPPERS AND OTHER INSECT PESTS IN THE NORTHERN GREAT PLAINS
Location: Pest Management Research Unit
Title: Cover crop and conidia delivery system impacts on soil persistence of Metarhizium anisopliae (Hypocreales:Clavicipitaceae) in sugarbeet
Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2012
Publication Date: November 1, 2012
Citation: Boetel, M.A., Majumdar, A., Jaronski, S., Horsly, R.D. 2012. Cover crop and conidia delivery system impacts on soil persistence of Metarhizium anisopliae (Hypocreales:Clavicipitaceae) in sugarbeet. Biocontrol Science and Technology. 22(11): 1284-1304.
Interpretive Summary: Previous research has shown that combination of the insect pathogenic fungus, Metarhizium, with oat or rye cover crop was better than either alone in managing damage from the sugarbeet root maggot in that crop. The currently described research examined one possible reason why this improvement occurred – greater persistence or even increase in fungus levels due to the presence of an oat or rye root system. Data from three years of fields trials indicated that fungus delivered on nutritive granules grew and increased in numbers, but trends were inconsistent, possibly due to inter-year differences in rainfall. Spores delivered in a spray to the soil surface beneath young plants (where the SBRM flies lay their eggs) persisted up to 30 days.
The sugarbeet root maggot, Tetanops myopaeformis (Röder), is a major North American pest of sugarbeet, Beta vulgaris L. Previous research suggests moderate field efficacy of the fungal entomopathogen Metarhizium anisopliae (Metch.) Sorok. against T. myopaeformis larvae. We conducted three-years of field trials (2002-2004) to assess the impacts of oat, Avena sativa L., and rye, Secale cereale L., cover crops on persistence of M. anisopliae isolate ATCC 62176 applied at 8 x 1012 viable conidia/ha by using corn grit granular or aqueous spray formulations to manage T. myopaeformis in sugarbeet. Significantly more colony forming units (CFUs) were detected immediately after application (0 days after treatment [DAT]) in spray plots than in granule-treated plots. However, ~76 to 92% declines in CFUs occurred in spray plots within 30 DAT. Substantially (i.e., 83 to 560%) more rainfall occurred in June of 2002 than in June of any other year during the study. Subsequently, 71 to 670% increases in CFUs occurred by 60 DAT in M. anisopliae granule-treated plots established with oat or rye cover crops that year. CFU increases were higher in cover crops that year, but no significant cover effects were detected. Conidia persisted for up to 30 DAT in M. anisopliae spay plots and 60 DAT in granule-treated plots in 2002; however, no increases occurred in 2003 or 2004 (i.e., years with less June rainfall). Trends suggest that M. anisopliae spray applications result in greater conidia concentrations than granules at sugarbeet plant bases in June during T. myopaeformis oviposition and larval establishment on host plants. Increases are possible when the fungus is delivered via granular formulations, but moderate soil moisture at application time, followed by relatively high postapplication rainfall may be necessary for conidia production.