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Effects of low levels of herbicides on prairie species of the Willamette Valley, Oregon
Citation:
Olszyk, D., M. Blakeley-Smith, T. Pfleeger, EHenry Lee, AND Milt Plocher. Effects of low levels of herbicides on prairie species of the Willamette Valley, Oregon. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 32(11):2542-2551, (2013).
Impact/Purpose:
Government agencies, such as EPA’s Office of Pesticide Programs (OPP) need improved tools to predict potential effects of chemical herbicides on ecological endpoints for non- agricultural plant ecosystems especially as they relate to wildlife habitat and the viability of threatened and/or endangered plant species. To provide data for ecological risk assessments, the current EPA required tests assess effects to non-target plants currently use ten angiosperm species, usually crops. The narrow taxonomic and life form range of the ten required test species sufficiently test the impacts of herbicides on native species. To address the need for improvements in plant testing protocols and for data on potential responses of non-crop plants, research was conducted on the effects of three herbicides (glyphosate, tribenuron and fluazifop) on vegetative growth of 17 seventeen native and introduced plant species which occur in a critically rare grassland ecosystem in Oregon’s Willamette Valley. Our results indicated a range in sensitivity by non-crop plants to each of the three herbicides tested. Certain non-crop plants exhibited significant reductions in biomass following exposure to very low levels of herbicide, while other species were completely tolerant. Our results illustrated the potential usefulness of non-crop species in phytotoxicity testing. Use of these species would make OPP’s ecological risk assessments more applicable to potential real-world herbicide drift situations, by better illustrating potential impacts on important native plant communities that would data based on crop plants. Our results also indicate the potential to use herbicide response data in habitat restoration where known differences in herbicide sensitivity can be used to manipulate plant communities. For example, the three introduced species used in this study can each be controlled with one of the tested herebicides: glyphosate (Festuca arundinacea), tribenuron (Leuccanthemum vulgare), and fluazifop (Cynosurus echinatus), respectively.
Description:
Non-crop plants (native and introduced) growing adjacent to agricultural fields provide essential habitat for wildlife and pollinators, and may be exposed to low levels of non-target pesticide drift during routine weed control activities. This study evaluated the relative sensitivity of 17 non-crop plant species from Oregon’s Willamette Valley to herbicides used locally for pest plant control in agricultural fields. The herbicides tested were glyphosate, tribenuron methyl (tribenuron) and fluazifop-P-butyl (fluazifop). There was a wide range of responses among species for each herbicide. For glyphosate; Elymus trachycaulus, Festuca arundinacea, Madia elegans, Potentilla gracillis and Ranunculus occidentalis were the most sensitive species, based on inhibitory concentrations calculated to reduce shoot dry weight by 25% (IC25 values) of 0.02 to 0.04 × a field application rate (F.A.R.) of 835 g active ingredient hectare (g a.i. ha-1) . Clarkia amoena and Lupinus albicaulis were the most tolerant to glyphosate, with IC25 values near the field application rate. Three forb species (Clarkia amoena, Prunella vulgaris and Ranunculus occidentalis), were the most sensitive to tribenuron based on IC25values of 0.001 to 0.004 × F.A.R. of 8.7 g a.i. ha-1 for reductions in shoot dry weight. Five grass species were tolerant to tribenuron with no significant IC25 values. Fluazifop primarily affected grass species, as expected due to the grass-specific activity for this herbicide. Two native grasses, Elymus trachycaulus and Danthonia californica were the most sensitive, with IC25values of 0.007 and 0.013 × F.A.R. of 210 g a.i. ha-1, respectively, for shoot dry weight. Another native fescue grass, Festuca roemeri, and nearly all the forb species were tolerant to fluazifop, showing little or no response at any herbicide rate. Our results indicated a range in sensitivity by non-crop plants to each of the three herbicides tested. Certain non-crop plants exhibited significant reductions in biomass following exposure to very low levels of herbicide, while other species were completely tolerant. Our results indicate the potential to use herbicide response data in habitat restoration where known differences in herbicide sensitivity can be used to manipulate plant communities. For example, the three introduced species used in this study can each be controlled with one of the tested herbicides: glyphosate (Festuca arundinacea), tribenuron (Leucanthemum vulgare), and fluazifop (Cynosurus echinatus), respectively.