Cover crop and conidia delivery system impacts on soil persistence ofMetarhizium anisopliae(Hypocreales: Clavicipitaceae) in sugarbeet

Abstract

The sugarbeet root maggot, Tetanops myopaeformis (Rôder), is a major North American pest of sugarbeet. Beta vulgaris L. Previous research suggests that moderate T. myopaeformis control is possible with the entomopathogen Metarhizium anisopliae (Metch.) Sorok. We conducted a three-year (2002)(2003)(2004) experiment to assess impacts of" oat. Avena sativa L. and rye. Sécale céréale L., cover crops on persistence of corn grit-based granular or spray formulations of M anisopliae isolate ATCC 62176 (i.e. MA 1200) applied at 8 x lO'^ viable conidia/ha in sugarbeet. More colony forming units (CFUs) were detected immediately after application [0 days after treatment (DAT)] in spray plots than granule-treated plots. However, 76-92% declines in CFUs per gram of soil occurred in spray plots within 30 DAT. Substantially (i.e. 83-560%) more rainfall occurred in June 2002 than during June of any other year. Subsequently, 71-670% increases in CFU concentrations occurred by 60 DAT in M anisopliae granuletreated plots with oat or rye cover crops that year. CFU density increases were higher in cover crops in 2002, but no significant cover crop effects were detected. Conidia persisted for up to 30 DAT in M anisopliae spray plots and 60 DAT in granule-treated plots in 2002; however, no increases occurred in the years with less June rainfall. Trends suggest that M. anisopliae aqueous sprays result in greater conidia concentrations than granules at sugarbeet plant bases in June during T myopaeformis oviposition and larval establishment on host plants. Increases are possible when delivering conidia via granules, but high post-application rainfall could be necessary for conidia production.

Systemic Colonization by Metarhizium robertsii Enhances Cover Crop Growth

“…In a field experiment to determine the effects of winter cover crop diversity in an annual cropping system on a variety of ecosystems services, detection of M. robertsii was lower in treatments with brassica cover crops as compared to those with legume cover crops [44]. Survival of conidia of formulated M. anisopliae applied to cereal rye and oat cover crops in a sugarbeet production system was greater in oat than in cereal rye, and the authors suggested that allelopathic compounds from cereal rye may have suppressed M. anisopliae [45].…”