You are here:
Plant reproduction is altered by simulated herbicide drift to constructed plant communities
Citation:
Olszyk, D., T. Pfleeger, T. Shiroyama, M. Blakeley-Smith, EHenry Lee, AND M. Plocher. Plant reproduction is altered by simulated herbicide drift to constructed plant communities. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 36(10):2799-2813, (2017).
Impact/Purpose:
This study indicated potential unintended consequences of low levels of chemical herbicides to reduce native plant seed production, and demonstrated an experimental protocol whereby a plant community can be evaluated for ecological responses. Modern intensive agriculture is dependent on herbicides to control “weeds”, plants which compete with our crops for resources thereby reducing the amounts of marketable products. However, when these herbicides are applied in the air, they can drift from the “target” field given the right environmental conditions. Intensive agricultural has also reduced the extent of native vegetation which provides valuable ecosystem services such as pollination and support of desirable insect populations. We studied the potential consequences of herbicide drift to “nontarget” native vegetation, focusing on seed production which is essential for the future survival of plant populations. The experiments were conducted with a constructed community of 9 Willamette Valley native plant species in field plots to simulate natural conditions. We used two herbicides, glyphosate and dicamba, singly and in combination. Mixtures of these herbicides may become more widespread in the future as crops are genetically modified to be tolerant of both chemicals for enhanced weed control. We showed a reduction in seed production with a simulated drift level of little as 1/100 of the normal field application rate of the individual or combined herbicide for the most productive species, Oregon sunshine. Even more significant was the large increase in immature seeds with herbicide treatments which could reduce seed viability and success of future generations for the species. Collectively these results point out the importance of considering ecological responses, including seed production, in risk assessments for regulation of herbicides to prevent adverse effects to desirable native plants.
Description:
Herbicide drift may have unintended impacts on native vegetation, adversely affecting structure and function of plant communities. However, these potential effects have been rarely studied or quantified. To determine potential ecological effects of herbicide drift, we constructed a series of small plant community plots using perennial species found in Willamette Valley Oregon grasslands including: 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 strawberry), and Potentilla gracilis (slender cinquefoil). Studies were conducted on two Oregon State University farms over two years, and evaluated single and combined effects of drift rates of 0.01 to 0.2 x field application rates (FAR) of 1119 g ha-1 for glyphosate [active ingredient (a.i) of 830 g ha-1 acid glyphosate] and 560 g ha-1 a.i. for dicamba. Species response endpoints were % cover, # of reproductive structures, mature and immature seed production (dry weight), and vegetative biomass. Herbicide effects differed with species, year and farm. Among the more notable responses, Eriophyllum lanatum had a significant reduction in total seed production or % immature seed dry weight with as little as 0.01 x FAR of dicamba, glyphosate or the combination of both herbicides; but a significant reduction in % cover near the end of the growing season only with 0.2 x FAR of both herbicides. Elymus glaucus had a significant reduction in total seed production with 0.1 x FAR of glyphosate alone or in combination with dicamba in one year. The other species showed similar trends but had fewer significant responses. These studies indicated potential unintended effects of low levels of herbicides on reproduction of native plants, and demonstrated an experimental protocol whereby a plant community can be evaluated for ecological responses.
