Microbial weed control: an off-beat application of plant pathology

In plant pathology, a thorough understanding of pathogen–host–environment interactions is required to develop disease control methods that will be detrimental to the pathogen and ultimately protect the plant. The same disease-conducive conditions can be utilized in a nontraditional way, as with the bioherbicide approach to weed control, to benefit the pathogen and cause harm to the plant. Potential biocontrol organisms should be investigated for the six following aspects to determine their biological and ecological characteristics: (i) identification of the causal agent, (ii) pathogenicity and disease development on a range of plant species, (iii) pathogen mechanisms involved in infection of the host, (iv) potential plant defense responses, (v) genetic variability in the pathogen and the host, and (vi) environmental influences on the host and the pathogen. The potential of plant pathogens as bioherbicides is described using Alternaria cirsinoxia for control of Canada thistle (Cirsium arvense) as a case study.