Biological Control of Rangeland Weeds

Weedy forbs and brush cost America’s range managers at least $1.7 billion/year. Biological controls, or “the planned use of living organisms to reduce the vigor, reproductive capacity, density, or effect of weeds,” should be considered and included in pragmatic integrated weed management systems for rangelands. Various approaches to biocontrol under that definition are discussed. These include foreign exploration and introduction of exotic insects, notes, and plant pathogens as biocontrol agents; augmentation of native biocontrol agents, especially plant pathogens; grazing systems; and positive and aversion conditioning for various classes of livestock to use against troublesome weeds or brush or to avoid palatable poisonous weeds. USDA’s Agricultural Research Service has at least nine laboratories, worldwide, devoted to research on various aspects of biocontrol of exotic and native rangeland weeds. The usual goal of biocontrol is to improve ecological systems by using biotic agents to restore target plant species to lesser competitive intensities or to negate their effects so that they do not overwhelm plant communities or cause damage to livestock. The usual results of biocontrol are: improved agricultural production, improved ecosystem functions and status in terms of species richness and diversity of plant and animal communities, and improved protection of rare species. Regardless of whether target weeds are introduced or native, researchers must make balanced evaluations of risks, benefits, and the potential for success in developing biological control programs.