A Reflection on My Research in Weed Biological Control: Using What We Have Learned for Future Applications

When I began my foray into the field of biological control of weeds in 1971, the concept of deliberately using pathogens to control weeds was novel and untested and met with skepticism and resistance. Soon, a worldwide network of plant pathologists, weed scientists, microbial technologists, formulation specialists, and regulatory personnel came together to study, develop, and apply pathogens in safe and effective ways of control of a variety of weeds in crops and natural areas. Several new weed–pathogen systems were studied; a few dozen products and pathogens were brought to use, albeit on a very small scale compared to conventional weed-control products; and along the way, some valuable lessons were learned in phytopathology and weed ecology. A seminal body of information was published on the etiology and epidemiology of several diseases of weeds, many new pathogens were discovered and described, and methods were developed for mass production, formulation, and storage of pathogens. Numerous pathogen-produced herbicidal metabolites were discovered and characterized. Protocols were developed, tested, and applied for safe importation and release of exotic pathogens and for registration of microbial herbicides. Spectacular success was achieved with some pathogens used as classical biocontrol agents, and a new class of herbicide, the bioherbicides, came on the scene. Yet some key opportunities were missed. Notably, weed biocontrol research remained largely preoccupied with agent or product development and deployment while great strides were made during this period in phytopathology to understand the genetic–molecular basis of virulence, host range, host specificity, host response to infection, cell death, and pathogen population structure. Nevertheless, the accomplishments in the field of weed biocontrol by pathogens are truly significant. Certainly, we are poised to apply the knowledge gained toward discovery and development of additional weed-control pathogens, but increased effort should be directed also at using pathogen genes, gene products, and genetic mechanisms for weed control. An investment in the latter could help us gain insights into genetically programmed host–pathogen interactions that may be exploited to kill weeds, restrain weed growth, or knock out traits for invasiveness. In our continuing struggle to manage weeds, biocontrol with pathogens should remain a major thrust. Here I present perceptions I have gained from the work that my students, postdoctoral and technical associates, colleagues, and I have done with several weed–pathogen systems.