Survey and evaluation of fungal pathogens for biological control of grass weeds
Wild oats and green foxtail rank as the most abundant annual grass weeds in the Canadian prairies. Prolific seed production, life cycle similarities to cereal crops and the development of herbicide-resistance make these weeds major pests. Extensive surveys for microbial weed control agents (foliar and soil-borne) were conducted from 1994 to 1996. In detached leaf bioassays, 36 foliar fungal agents from green foxtail and 24 from wild oats were pathogenic. Out of 70 soil-borne fungi isolated from roots and crowns of wild oat plants, nine isolates reduced germination by 90% or greater in growth pouch bioassays. Soil application of the mycelium at a concentration of 0.8% (w/v) resulted in lower weed emergence over a 3-wk period. Adjuvants improved efficacy of three foliar agents for green foxtail control. Spray application method also had an impact on the efficacy of foliar biocontrol agents. Application with an airbrush provided superior control over a flat-fan nozzle, but with higher water volumes (1800 L/ha), a flat fan nozzle provided similar control to that exhibited with the airbrush. Development of suitable formulation and application methods will be important for preserving efficacy under more practical application conditions.
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