Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2011
Publication Date: 6/1/2007
Citation: Ables, C.Y., Rosskopf, E.N., Charudattan, R. 2007. Plant Pathogens at Work: Progress and possibilities for weed biocontrol classical versus bioherbicidal approach. Online. Plant Health Progress doi:10.1094/PHP-2007-0822-01-RV. Interpretive Summary: Biological control of weeds with plant pathogens utilizes two basic approaches referred to as the classical approach and the inundative or bioherbicide approach. In the classical approach, pathogens of non-native invasive weeds are sought from the weed's center of origin. The pathogens are then rigorously tested for their ability to cause disease on the target plant while causing no damage to non-target plants. Generally, pathogens intended as classical biocontrol agents are subjected to rigorous safety and host-specificity testing under the oversight of the Technical Advisory Group (TAG) on Biological Control of Weeds. TAG, a voluntary committee under the aegis of the U.S. Department of Agriculture-Animal and Plant Health Inspection Service-Plant Protection and Quarantine (APHIS-PPQ), consists of representatives from several federal agencies. TAG’s role is to help coordinate research aimed at assuring safety in biological weed control introductions. TAG plays an oversight role in reviewing proposals to initiate classical weed biocontrol projects and in making recommendations with respect to the need, scope, and adequacy of the proposed research. Based on TAG’s recommendation, APHIS-PPQ grants permits to introduce foreign pathogens into approved quarantine facilities as well as their eventual release and field establishment, usually after additional safety evaluations have been completed and reviewed and the findings deemed acceptable by TAG. The bioherbicide approach uses endemic fungi applied at high enough inoculum rates to cause severe disease on the target weed. The agents are also tested for their safety with regard to non-target plants. The use of these pathogens as biologically-based herbicides is regulated by the Environmental Protection Agency under the Federal Insecticide, Fungicide, and Rodenticide Act. Some of the successes in classical control and commercialized products resulting from bioherbice research are reviewed. Novel approaches for researching and developing bioherbicides is also explored.
Technical Abstract: Weeds are a perpetual problem for agriculture, causing significant reductions in the quantity and quality of crop yields. Weeds also incur extra costs related to harvesting and increase production costs through the need for mechanical, chemical, and biological inputs for their management. Based on dollars spent, herbicides are the most commonly used pesticide in the United States. In addition to reducing agricultural production, weeds also pose serious ecological problems; invasive weeds in natural areas may alter ecosystem processes and displace native plant and animal species. They may also support populations of non-native animals and microbes and hybridize with native species, which may subsequently alter gene pools. In addition, weeds serve as reservoirs for plant pests that impact crops. Adding to the economic and ecological impacts of weeds are the environmental impacts associated with weed control agents and practices, such as chemical herbicides, cultivation, and tillage. The negative effects of existing weed control practices coupled with the loss of registration for some herbicides, the recent ban on methyl bromide, lack of herbicides labeled for weeds of minor crops or non-agricultural weeds and non-native invasive weeds, the cost of control methods in natural other low-maintenance areas, and the need for control methods that are appropriate for use in organic production systems pose a great challenge for both researchers and growers. Many of these challenges create niches where the use of plant pathogens as biological control agents for weeds could be a viable alternative. Both the classical and inundative or bioherbicide approaches are reviewed and some examples of successful programs using both approaches and specific areas of interest in the bioherbicide approach are also discussed.