ABSTRACT
The application of biological control for the management of weed populations has generally been viewed as an environmentally sound additional approach to chemical herbicides (Boyetchko et al. 2002; Mortensen 1998; Rosskopf et al. 1999). Bioherbicides are often described as the intentional use of plant pathogens that are mass-produced, formulated, and applied at high inoculum rates in a similar fashion as chemicals. Although a variety of microbial agents may be used, host-specific fungal pathogens often referred to as mycoherbicides, have been studied more extensively for biocontrol of weeds. In comparison, classical biological control involves the importation of natural enemies and relies on the natural survival, dissemination, and self-perpetuation of the living agent for control of weeds below ecological thresholds. The classical approach is often considered more appropriate for low management systems such as pasture and rangeland where site disturbance is minimal, while bioherbicides are ideal for singleseason management of agricultural and forest weeds where site disturbance is the norm. Despite many economic, social, and environmental benefits ascribed to biological control, it is reasonable to ask why more bioherbicide or mycoherbicide products are yet to become widely available in the marketplace. Many researchers would argue that there has been a great deal of progress, with several additional microbial agents identified as potential bioherbicides and innovative improvements in mass-production, formulation, and application of living organisms. Despite the various accomplishments by researchers world-wide (Boyetchko et al. 2002; Charudattan 2001), the question remains whether we have made significant advancements in bioherbicide research that would facilitate increased adoption of this technology. Several reviews have discussed in great detail some of the limitations associated with bioherbicides (Auld and Morin 1995; Makowski 1997; Mortensen 1998), including biological, environmental, and technological constraints. Critics have attributed these constraints to the lack of further development of many biocontrol agents. This review will provide an update on the status of mycoherbicide research, summarize some of the challenges encountered, and provide some thoughts on potential new approaches that may be used to address these challenges in order to advance the development of promising mycoherbicide candidates.
