Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Experiment Station
Publication Acceptance Date: February 8, 1999
Publication Date: N/A
Interpretive Summary: The sugarbeet root maggot is a serious insect pest of sugarbeet in North America. Larvae feed on developing sugarbeet by tunneling along the root surface. Feeding causes yield loss by reducing stands early in the season and/or reducing root yields at harvest. Insecticide applied at planting is the primary control method. The extensive use of only a few insecticides is conducive to the development of insecticide resistant root maggot strains. Current insecticides may also become unavailable because of environmental concerns. Biocontrol agents provide an alternative to current chemical insecticides. The entomopathogenic fungi Metarhizium anisopliae has been the most successful root maggot biocontrol agent we have identified, to date. Damage ratings and yield data from preliminary field studies indicate that a fall (preceding planting) plus spring (planting time) application of fungi provides better control than a single application either spring or fall.
Technical Abstract: Only a few insecticides are available for controlling the sugarbeet root maggot (Tetanops myopaeformis). These could become less effective because of the development of resistant root maggot strains or become unavailable because of environmental concerns. An effective biocontrol agent would provide an alternative and, perhaps, more consistent control method. Laboratory results and a 1995 field trial prompted further testing of the entomopathogenic fungus Metarhizuim anisoplaie. Metarhizium inoculum was prepared by culturing the fungus on heat-killed barley. The inoculated barley was spread evenly over field plots in the fall proceeding the sugarbeet crop, in the spring prior to planting, or both in the fall and spring. Root yields ranged from 49.5 Mg ha-1 when no insecticide was applied to 59.2 Mg ha-1 when Lorsban (chlorpyrifos) was used to control maggots. The fall, spring, and fall plus spring applications of Metarhizium yielded 51.5, 50.9, and 58.9 Mg ha-1, respectively, at Crookston in 1996. The 1997 trials included the same three Metarhizium treatments with an additional application of Metarhizium in the spring of 1996 (prior to planting barley). Root yields for the Metarhizium treatments ranged from 51.4 to 57.5 Mg ha-1, compared to 57.6 Mg ha-1 when Lorsban was applied and 48.7 Mg ha-1 in the absence of maggot control in 1997. Yield differences between treatments were not significant in 1998 because of reduced root maggot pressure, but appeared to follow the pattern observed in the 1996 and 1997 trials. Results have been encouraging; however, additional information on application rates/timing, formulations, and the effectiveness of Metarhizium in more environments will be required