Submitted to: Journal of Sugarbeet Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2000
Publication Date: 7/1/2000
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 conductive 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 von Roder). These could become less effective because of the development of resistant root maggot strains or become unavailable because of environmental concerns. Laboratory results suggested the entomopathogenic fungus, Metarhizium anisopliae (Metschnikoff) Sorokin, had potential as a root maggot control agent and prompted field testing. Metarhizium inoculum was spread evenly over field plots in the fall preceding the sugarbeet (Beta vulgaris L.) crop, in the spring prior to planting, or both in the fall and spring. In 1995 trials at Hillsboro, North Dakota, the no-insecticide treatment yielded 32.6 Mg ha-1, compared with 48.7 Mg ha-1 when a chemical insecticide was used. Root yields from the Metarhizium treatments ranged from 33.2 to 42.2 Mg ha-1. Four-year (1996-99) average recoverable sugar yields at Crookston, Minnesota were 7161 kg ha-1 when no insecticide was applied, 8120 kg ha-1 when a chemical insecticide was used, and 8622 kg ha-1 when Metarhizium was applied in the spring and fall. Results, to-date, have been encouraging; however, information on application rates and timing, formulation, and the effectiveness of Metarhizium in more environments is required before commercialization is feasible.