Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Abstract Only
Publication Acceptance Date: 1/10/2003
Publication Date: 1/21/2003
Citation: MAJUMDAR, A., BOETEL, M.A., JARONSKI, S., DREGSETH, R., SCHROEDER, A. INTEGRATION OF A FUNGAL ENTOMOPATHOGEN AND CEREAL COVER CROPS FOR SUGARBEET ROOT MAGGOT MANAGEMENT - FIRST YEAR TRIAL. SUGARBEET RESEARCH AND EXTENSION REPORTS. 2003. v. 33. p. 163-169. Interpretive Summary: Sugarbeet Root Maggot (SBRM) Tetanops myopaeformis (Röder) is the most damaging pest of sugarbeet throughout the Red River Valley (RRV). 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 a tritrophic interaction between treatments: cover crop (by providing modified soil microhabitat), the biocontrol agent (by improved persistence of Metarhizium), and the host in sugar beets. 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, only few reports suggest an association between cover crop and effects on entomopathogens. Therefore first-year research should be considered a preliminary study that will be continued in the 2003 field season.
Technical Abstract: The chief objective of this study was to evaluate a combined approach to SBRM control that integrates the microhabitat stability provided by a cover crop with different formulations of Metarhizium anisopliae MA-1200 for enhanced effectiveness. Overall, the study aimed at developing a sustainable, cost-effective SBRM management strategy for growers in the Red River Valley of North Dakota and Minnesota. This field experiment was established near St. Thomas (Pembina Co.) in North Dakota in 2002. A split-plot field design was used with two cereal cover crops (oat and rye) as main treatments, three seeding rates of 0, 1.5 and 3.0 oat bushel equivalent as the sub-treatments, and MA-1200 granular and liquid 2X formulations, Counter 15G@1.5 pound (AI)/ac, and no treatment as the sub-sub treatments. There were 20 treatments in the experiment. The results indicate that the granular treatment of Metarhizium was sensitive to cover crop type. The same interaction occurred when the two cover crops were contrasted without any treatment. However, the Metarhizium foliar treatment did not respond to cover crop type. Thus in 2002 oats at high seeding rate showed good response with granular Metarhizium than at low seeding rate. This tells us that a dense canopy achieved by higher seeding rate of oat cover crop can provide good protection to Metarhizium granules (planting-time) applied in-furrow, probably by conserving soil moisture and lowering soil temperature. Main conclusions from 2002 field experiment are as follows: (1) Metarhizium formulations perform better when integrated with cover crop ; (2) More research is needed to design the best integrated approach for sustainable SBRM management using entomopathogens. This experiment suggests 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 be keeping 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 preliminary with continued studies in the 2003 field season.