|Majumdar, Ayanava - NORTH DAKOTA STATE UNIV|
|Boetel, Mark - NORTH DAKOTA STATE UNIV|
|Dregseth, Robert - NORTH DAKOTA STATE UNIV|
|Schroeder, Allen - NORTH DAKOTA STATE UNIV|
Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 16, 2006
Publication Date: November 1, 2006
Citation: Majumdar, A., Boetel, M., Jaronski, S., Dregseth, R.J., Schroeder, A.J. 2006. Cereal cover crops and a microbial insecticide for integrated control of sugarbeet root maggot. Sugarbeet Research and Extension Reports. 36:222-227. Interpretive Summary: Our overall goal is to develop an integrated program for management of the sugarbeet root maggot (SBRM) to provide sustainability to sugarbeet production in areas affected by the pest. The specific objective of this study was to assess the impact of oat and rye cover crops integrated with Metarhizium anisopliae strain F52 in sites subject to moderate and high SBRM infestations. We also determined optimal deployment methods (i.e., formulation + application technique) and timing of M. anisopliae applications to maximize root maggot control. Rye cover integrated with a microbial insecticide reduced root maggot feeding injury under high SBRM pressure. Oat seems more flexible and effective than rye for integration with bio-based SBRM management programs involving the use of M. anisopliae for managing SBRM. A high seed rate of cover crops seems to integrate better with chemical or biological insecticides under most situations. Fungus granules consistently provided high root protection from SBRM larvae at both test locations.
Technical Abstract: Our overall goal is to develop an integrated program for management of the sugarbeet root maggot (SBRM) to provide sustainability to sugarbeet production in areas affected by the pest. The specific objective of this study was to assess the impact of oat and rye cover crops integrated with Metarhizium anisopliae strain F52 in sites subject to moderate and high SBRM infestations. We also determined optimal deployment methods (i.e., formulation + application technique) and timing of M. anisopliae applications to maximize root maggot control. Twenty treatments were arranged in a split-split-plot design at two sites in the Red River Valley of North Dakota. Main treatments were oat and rye covers; sub-level treatments were three seeding rates; sub-sub-level treatments were four insecticidal (Metarhizium and chemical) treatments, including an untreated control. Strain F52 of M. anisopliae was applied at 8x10exp12 viable conidia/ha, 22.4 kg product/ha) in the form of a planting-time granules or as an aqueous band-over-row spray at initial fly oviposition, at the rate of 5x10exp13 conidia/ha. At the St. Thomas ND site, rye at 3.0 Oat-Bushel-Equivalents (OBE) with M. anisopliae granules, spray, or 15% granular terbufos had low damage ratings (ranging from 3.1 to 3.3); root yield and recoverable sucrose yield were also significantly different from the untreated check. Stand-alone rye and oat (3 OBE) plots had damage ratings and yields that were not significantly different from the untreated check. Terbufos efficacy was enhanced slightly by the cover crops. In general, the oat + terbufos combinations had higher root and sucrose yield than rye + terbufos combinations. Rye plots, at both 1.5 and 3.0 OBE/ac, incurred heavy root maggot feeding injury (DR = 4.2 to 5.0) in the absence of an insecticide application. This was not seen with oat. Stand-alone oat had lower damage ratings (DR = 3.6 to 3.9) than plots with only rye. At the Minto site, where pest pressure was much lower, plots treated with oat at 3 bu/ac integrated with a postemergence M. anisopliae spray had the lowest incidence of root scarring, and produced high root and sucrose yields. High and low seeding rates of oat combined with M. anisopliae granules produced some of the highest root yield (>20 T/ac) and recoverable sucrose (>6500 lb/ac) in this trial. Yields from plots that received terbufos and an oat ground cover generally exceeded those from plots treated with granular fungus + oat treatments. Thus, oat appears to be a good candidate for integration with this biological control agent. M. anisopliae applications as stand-alone treatments resulted in significantly lower root and sucrose yields compared to integrated approaches where a cover crop was also included. Rye cover crops, at 1.5 or 3.0 OBE/ac, did not provide consistent success when integrated with M. anisopliae.