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The effects of glyphosate and aminopyralid on an artifical plant communities
Citation:
PFLEEGER, T. G., M. Blakeley-Smith, G. KING, E. LEE, AND M. PLOCHER. The effects of glyphosate and aminopyralid on an artifical plant communities. Presented at SETAC North America 32nd Annual Meeting, Boston, MA, November 13 - 17, 2011.
Impact/Purpose:
The US EPA has responsibility for registration of pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).
Description:
The US EPA has responsibility for registration of pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). The potential adverse effects of pesticides to nontarget terrestrial plant communities are a concern that must be addressed in the pesticide registration process. The protection of nontarget terrestrial plants requires a tiered approach using two single species greenhouse tests with an increasing level of test sophistication being required if a compound fails at the preceding tier. This can culminate in field testing which currently is not well-defined. Our objective was to develop a simple, economical, and geographically flexible field test with ecologically significant endpoints. Three plant species native to Oregon: Clarkia amoena (Farewell to spring), Prunella vulgaris (Self-heal), Festuca roemeri (Roemer’s fescue) were grown together along with a fourth introduced species, Cynosurus echinatus (Bristly dogtail grass). The experiment was replicated at two research farms within the Willamette Valley, Oregon. Round up Original (41% glyphosate) was applied at 0, 0.01, 0.1, and 0.2 x FAR (Field Application Rate) (32 fluid oz/acre (2.34 l/ha) roundup). Milestone (40.6% aminopyralid) was applied at 0, 0.037, 0.136, and 0.5 x FAR (7 fluid oz/acre (.51 l/ha) milestone). One third of the plots received a single application, 1/3 received two applications and 1/3 received three applications at the above listed rates. The control was a no spray treatment. Herbicide applications were two weeks apart. Plant height and width, in two perpendicular directions, were measured every two weeks during the growing season. Periodically, buds and flowers were counted and seeds were collected. Differences between sites were minor. Increasing the number of applications had less than an additive effect. Plant volume decreased with increasing glyphosate concentration. Clarkia died at all concentrations of aminopyralid while Festuca and Prunella increased in volume. Cynosauruas increased in volume at the lowest concentration of aminopyralid while decreasing at the highest concentrations. Flowering was delayed in Clarkia when exposed to glyphosate. The results indicate that simple field tests can be successfully performed to investigate the ecological effects of herbicides on nontarget plant interactions. We found that simple physiologically based greenhouse toxicity testing is not a reliable predictor of ecological outcomes in the field.