Submitted to: Society for Invertebrate Pathology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2003
Publication Date: 7/26/2003
Citation: MAJUMDAR, A., BOETEL, M.A., JARONSKI, S., DREGSETH, R., SCHROEDER, A. INTEGRATION OF METARHIZIUM ANISOPLIAE AND COVER CROPS FOR CONTROLLING SUGARBEET ROOT MAGGOT. SOCIETY FOR INVERTEBRATE PATHOLOGY ANNUAL MEETING. BURLINGTON, VT, JULY 26-30 2003. ABSTRACT. P. 71. Interpretive Summary: Interpretive Summary: Sugarbeet Root Maggot (SBRM) Tetanops myopaeformis (Röder) is the most damaging pest of sugar beets throughout the Red River Valley (RRV). Damage to sugarbeet crop can range between 9 to 85 percent within a season and averages about 40 percent without effective chemical control. Currently, measures for controlling this insect pest are primarily focused on the chemical tactics and, to a limited extent, on cultural practices. Due to high toxicity and environmental side effects, many of the conventional insecticides used by sugarbeet growers are under review by the Environmental Protection Agency (EPA). Control of the maggot by the fungus Metarhizium anisopliae strain MA1200 is currently under study. The chief objective of this study, was to evaluate a combined approach to SBRM management that integrates the microhabitat stability provided by a cover crop with different formulations of the fungus. Specifically, the research reported sought to evaluate the effects of an oat or rye cover crop, into which sugar beets were planted, and use of an entomopathogenic fungus for the control of the insect. Oats or rye were seeded at different densities This experiment suggested tritrophic interactions between treatments: cover crop (by providing modified soil microhabitat), the biocontrol agent (by improved persistence of Metarhizium), and the host (better control of SBRM) in sugarbeet cropping system. Further, retention of soil moisture and cooler temperature in the top soil may have kept maggots in the treated zone causing higher mortality and protecting the sugarbeet tap root. However, currently only few reports suggest an association between cover crop and effects on entomopathogens. Therefore first-year research should be considered a trendsetter that will be reinvestigated in 2003 field season.
Technical Abstract: The sugarbeet root maggot, Tetanops myopaeformis (Röder), is the most damaging insect pest of sugarbeet in Minnesota and North Dakota. A study was conducted in 2002 at St. Thomas, North Dakota (Pembina Co.), for managing the sugarbeet root maggot, using planting time granular and postemergence liquid applications of Metarhizium anisopliae strain MA-1200 with two cereal cover crops'oat, Avena sativa L., and rye, Secale cereale L. The integration of cereal covers with M. anisopliae is a novel approach for insect biocontrol. A split-split-plot field design was used with oat and rye cover crops as the main treatments, seeding rates (0, 1.5, and 3.0 oat bushel equivalents [OBE] per ac) as sub-treatments, with MA-1200 formulations compared to terbufos 15G and an untreated control as sub-sub-level treatments. In 2002, the relative levels of control were evaluated on a 0 to 9 damage rating (DR) scale (0 = no visible feeding injury, 9 = 75% of root surface scarred). Under the moderate T. myopaeformis feeding pressure that developed (mean DR of 6.08 in untreated controls), MA-1200 provided significantly better root protection when combined with cover crops than treatments with no cover. Granular MA-1200 in the presence of oat at 3.0 OBE/ac had significantly lower root injury (mean DR=5.45) than in the absence of a cover crop (mean DR=6.70). Also, sugarbeet plots receiving postemergence foliar MA-1200 had significantly less root feeding injury when combined with the rye cover at 3.0 OBE/ac (mean DR=4.5) than their non-cover counterparts (mean DR=6.22). Findings from 2002 trial indicate this novel integrated strategy suggests positive tritrophic interactions between the target insect, the entomopathogen, and the cereal cover crops that result in effective T. myopaeformis management. The experiment will be repeated in 2003.