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NOVEL HERBICIDES
Impact/Purpose:
This research provides new tools to the Office of Pesticide Programs for assessing potential risks of herbicides to nontarget plants. A web-based GIS program will be accessible to the Program Office and Regions, for delineating areas, species, and uses that pose the highest potential risk. Updated test protocols, including regionally based species selection procedures, along with new methods for spatially explicit probabilitistic risk ananlysis, will be provided.
Description:
Low-dose, high-potency herbicides are defined as those herbicides with a maximum label application rate of 0.5 pounds of active ingredient per acre. Several classes of chemicals fall into this category, including the acetolactate synthase (ALSase) inhibitor herbicides, imidazolinones, sulfonylureas, triazolophyrimidine sulfonamides, isoxaflutoles, and pyrimidyl thio-benzoates. Given the increasing use of these types of herbicides, the FIFRA Science Advisory Panel (2001) recommended restructuring the Tier II risk assessment process to expand the number of species tested and the endpoints evaluated for assessing risks to nontarget plants. A revised set of protocols (seedling emergence, vegetative vigor and reproduction/developmental) for terrestrial plants is being developed utilizing a new set of species. Test species are being selected by agro-ecoregions within the United States. Species selected will meet one or more of the following criteria: 1) a dominant native plant, 2) a dominant cultivated species, 3) an important food or shelter plant for wildlife, or 4) a rare or endangered species of the ecoregion. Test end points include production (yield), reproduction and species interactions. Test scenarios include existing vegetation surrounding test plots such as field margins, as well as more structured designs where mixtures of plants are seeded/planted in various relative densities and proportions. This will provide information on changes in species composition and system dynamics, along with the more traditional endpoints of phytotoxicity or death. Because of the difficulty of setting up a comprehensive monitoring system to detect off-target incidents across the US, a system for localized and/or regional field monitoring is being developed using a GIS (geographical information system) approach. Potential trouble spots can be identified by overlay maps that include (but are not limited to): current herbicide use patterns, anticipated herbicide use patterns, climate (especially wind speed), crops, soils types, natural vegetation, endangered plant species, water resources and wildlife ranges. Risks from pesticides to ecologically and economically important plant resources can be determined at the regional and landscape level. Information generated regarding potential hazards of low-dose, high-potency herbicides to nontarget plant species needs to be combined with estimates of potential exposure to define the risk from use of existing or proposed substances. Given the geographically focused nature of plant species distributions, cropping practices, and herbicide use, a spatially explicit framework is being developed that allows for probabilistic risk determination.