Technological Factors

The feasibility of commercializing bioherbicide agents has often been dependent on the ease and economics of mass-producing and formulating large amounts of viable, stable, and highly efficacious microbial propagules (Auld and Morin 1995; Mortensen 1998; Slininger et al. 1998). It is generally believed that submerged liquid fermentation is the most efficient commercial mass-production method for most biocontrol agents (Jackson et al. 1996). Although general guidelines or common fermentation ingredients for medium composition are available in public domains (Stanbury et al. 1995), most commercial fermentation protocols are custom designed for a specific organism and details are generally treated as trade secrets. However, when a company licenses a bioherbicide technology, the ability to mass-produce the agent economically and market it at a cost that is affordable to farmers, represents a strong determining factor in its development and commercialization potential. Lack of reliable field performance due to inadequate formulation and application technology has often been cited as a major reason for the lack of progress in bioherbicides (Greaves et al. 2000; Peng et al. 2001). It has been claimed that suitable formulation technology may help address some of the environmental constraints, particularly moisture requirements that often hinder the advancement of bioherbicide candidates beyond the discovery and evaluation phase. Propagules of foliar-applied fungal agents generally require free water to germinate and penetrate weeds. This leaf wetness requirement and its interaction with the ambient temperature often determine the outcome of a mycoherbicide application (Zhang and Watson 1997). Often, researchers evaluate mycoherbicide candidates by spraying till runoff, thereby overestimating the potential of many bioherbicide candidates at the early stage of evaluation (Lawrie et al. 1999). Less stringent dew requirement may be an advantage for foliar agents, especially in semiarid climates such as the Canadian prairies, where rainfall is infrequent at critical periods (e.g., in the spring). Intermittent dew occurs more often than continuous dew, but germinated fungal spores under short dew periods are more sensitive to desiccation and UV irradiation (Green and Bailey 2000b), therefore, survival of the germlings is going to be the key to successful infection under intermittent dew.

these processes may impact the others. At any stage of evaluation, refinements or modifications to these processes, even minor, may result in significant improvements in mycoherbicide performance.

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