Biological Control of Weeds Using Plant Pathogens

Changes in program directions at the Saskatoon Research Centre have resulted in the organization of a research team equipped to develop microorganisms for the biological control of important agricultural weeds. This paper presents a brief introduction to the science of inundative biological control and an overview of the research progress made on controlling Canada thistle, wild oats, and green foxtail using fungi and bacteria. Chemical herbicides comprise the largest component of all pesticides used in the world (Bellinder et al. 1994). In Canada, weeds cause annual crop losses of $984 million and 60% of this loss occurs in western Canada (Swanton et al. 1993). Current pest management strategies rely heavily on chemical pesticides but repeated use of certain herbicides year after year has led to the development of herbicide resistant populations of weeds (Beckie and Morrison, 1993; Heap et al., 1993). Public concern about environmental and user safety of herbicides, along with the rising costs of agricultural inputs, has pressured governments and industry to develop more sustainable and integrated weed management strategies. Environmentally safe herbicides which are less persistent and more selective than most agrochemicals currently in use are desired. Weed control through biological means such as with plant pathogens, offers an additional approach that can complement existing cultural and chemical control methods. What is Biological Control? Biological control may use biotic agents (such as fungi, bacteria, and viruses) or metabolites produced by these agents to kill, suppress, inhibit or cause damage to specific weeds while leaving other plants unaffected. The two main types of strategies for controlling weeds through biological control are the classical and inundative approach (Charudattan, 1991). The classical approach involves an assisted release of a biotic agent followed by natural establishment and dissemination throughout a weed-infested area. The agent reduces the weed population below the socio-economic or ecological threshold and provides long-term control, with no requirement for reintroducing the agent ( Boyetchko, 1996). The inundative approach, often referred to as a bioherbicide or mycoherbicide (when fungi are used), involves the periodic application of a pathogen to the weed-infested area (Boyetchko, 1996). For bioherbicides, a