You are here:
The effects of low levels of herbicides on simple plant communities
Citation:
PFLEEGER, T. G., D. M. OLSZYK, E. LEE, G. KING, AND M. PLOCHER. The effects of low levels of herbicides on simple plant communities. Presented at SETAC North America, Portland, OR, November 07 - 11, 2010.
Impact/Purpose:
In the United States, the US Environmental Protection Agency has the responsibility for the registration of pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act.
Description:
In the United States, the US Environmental Protection Agency has the responsibility for the registration of pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act. Prior to registration applicants must demonstrate that their product will not adversely affect human health or the environment. The potential adverse effects of unintended pesticide movement to nontarget terrestrial plant communities are a major concern in the registration and re-registration of pesticides. For the protection of nontarget terrestrial plants this requires two simple, single species greenhouse tests with an increasing level of test sophistication required if a compound fails at the preceeding level. This culminates in a field test which currently is not well-defined. Our objective was to demonstrate a field test that is simple, economical, geographically flexible and with endpoints of ecological significance. 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 Oregon State University 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. The control was a no spray treatment. The same control was used for all treatments. Herbicide applications were two weeks apart. Each of the ten treatments was replicated ten times for each herbicide (glyphosate and aminopyralid) at each farm. Plant height and width, in two perpendicular directions, were measured weekly during the growing season. Every two weeks flowers were counted and seeds collected if present. Differences between sites were minor. 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 while decreasing at the highest concentrations of aminopyralid. 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 plant interactions. Greenhouse toxicity testing is not a reliable predictor of field results.