You are here:
Responses of a constructed plant community to simulated glyphosate and dicamba drift
Citation:
Olszyk, D., T. Pfleeger, EHenry Lee, T. Shiroyama, AND M. Plocher. Responses of a constructed plant community to simulated glyphosate and dicamba drift. Presented at Ecological Society of America, Sacramento, CA, August 10 - 15, 2014.
Impact/Purpose:
As part of its regulation of pesticides, the US Environmental Protection Agency must consider environmental risks, including impacts to nontarget plants exposed to pesticide drift. More sophisticated field tests using simulated plant communities may be required, but are rarely conducted. This study demonstrated experimental protocols whereby a plant community can be evaluated for ecological responses, giving the EPA better tools to consider environmental risks from herbicides. The studies also provides important new information indicating the potential effects of low levels of herbicides on reproduction of native plants. The plant communities included nine perennial species from Oregon’s Willamette Valley, an area which has been highly impacted by agriculture: Eriophyllum lanatum (Oregon sunshine), Iris tenax (toughleaf Iris), Prunella vulgaris var. Lanceolata (Lance selfheal) Camassia leichtlinii (large camas), Festuca roemeri (Roemer’s fescue), Elymus glaucus (blue wildrye), Ranunculus occidentalis (western buttercup), Fragaria virginiana (Virginia/wild strawberry), and Potentilla gracilis (slender cinquefoil). Exposure-response studies were conducted on two Oregon State University farms over two years. The studies evaluated the single and combined effects of simulated drift rates of two herbicides (glyphosate and dicamba) which are likely to be used in tank mixes in the future with crops that have been genetically modified to be resistant to both herbicides. Among the more notable responses, the largest species, Eriophyllum lanatum, had a significant reduction in total seed production with as little as 0.1 x FAR of dicamba, glyphosate or the combination of herbicides in one year, but a smaller and nonsignificant reduction in % cover.
Description:
Background/Questions/Methods As part of its regulation of pesticides, the US Environmental Protection Agency must consider environmental risks, including impacts to nontarget plants exposed to pesticide drift. Normally these risk assessments consider impacts to individual species, using greenhouse, exposure-response experiments with growth endpoints. More sophisticated field tests using simulated plant communities may be required, but are rarely conducted. To provide information on possible field test procedures to indicate pesticide effects on plant communities, we developed a series of small plots using species found in Willamette Valley Oregon grasslands. The communities included nine perennial species: Eriophyllum lanatum (Oregon sunshine), Iris tenax (toughleaf Iris), Prunella vulgaris var. Lanceolata (Lance selfheal) Camassia leichtlinii (large camas), Festuca roemeri (Roemer’s fescue), Elymus glaucus (blue wildrye), Ranunculus occidentalis (western buttercup), Fragaria virginiana (Virginia/wild strawberry), and Potentilla gracilis (slender cinquefoil). Exposure-response studies were conducted on two Oregon State University farms over two years. The studies evaluated the single and combined effects of drift rates of herbicides (0.01 to 0.2 x field application rates (FAR) of 1119 g ha-1 active ingredient (a.i) (830 g ha-1 acid glyphosate) for glyphosate. and 560 g ha-1 a.i. for dicamba). Response endpoints were % cover on a periodic basis, # of reproductive structures and seed production by species. Results/Conclusions Herbicide effects differed with species, year and site. Among the more notable responses, the largest species, Eriophyllum lanatum, had a significant reduction in total seed production with as little as 0.1 x FAR of dicamba, glyphosate or the combination of herbicides in one year, but a smaller and nonsignificant reduction in % cover. Elymus glaucus had a significant reduction in total seed production with 0.2 x FAR of glyphosate or the combination of herbicides in one year. The other species showed fewer responses. These studies indicated the potential effects of low levels of herbicides on reproduction of native plants, and demonstrated experimental protocols whereby a plant community can be evaluated for ecological responses.