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Glyphosate and Dicamba Inhibit Flowering of Native Willamette Valley Plants
Citation:
Olszyk, D., T. Pfleeger, EHenry Lee, T. Shiroyama, AND Milt Plocher. Glyphosate and Dicamba Inhibit Flowering of Native Willamette Valley Plants. SETAC, Orlando, FL, November 06 - 10, 2016.
Impact/Purpose:
Herbicides are routinely used to control weeds in agricultural fields, with unintended consequences if the herbicides drift and affect neighboring native plants. EPA’s Office of Pesticide Programs needs sound data to conduct their assessments of these potential ecological risks when regulating herbicides. Realistic assessments should consider significant aspects of plant development such as flowering, but these data rare. To address this need for ecological relevant data, we determined effects of simulated herbicide drift on flowering for nine native Willamette Valley plant species growing on two experimental farms and in two years. The studies evaluated the single and combined effects of two common 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. We found clear reductions in flowering due to the herbicides, even though the effects varied with species, farm and year. In some of the most notable effects, as little as 1/10 of a normal field application rate for dicamba or glyphosate reduced the number of plants that flowered for the species Oregon sunshine (Eriophyllum lanatum) and Lance self-heal (Prunella vulgaris). Thus, this study provides the EPA with important new information on the potential environmental risks from herbicides on flowering, which is critical not only for reproduction of plant species; but also because flowering of native plant species provides resources for pollinator insects which are critical for crop production. This work is associated with CSS 2.4.1
Description:
Successful flowering is essential for reproduction of native plants and production of food for herbivores. It is also an important alternative endpoint for assessment of ecological risks from chemical stressors such as herbicides. We evaluated flowering phenology after herbicide drift treatments for nine native Willamette Valley plant species grown together in small (0.45 x 0.45 m) field plots. Study taxa were: Eriophyllum lanatum (ERLA, Oregon sunshine), Iris tenax (IRTE, toughleaf iris), Prunella vulgaris var. lanceolata (PRVU, lance selfheal), Camassia leichtlinii (CALE, large camas), Festuca roemeri (FERO, Roemer’s fescue), Elymus glaucus (ELGL, blue wildrye), Ranunculus occidentalis (RAOC, western buttercup), Fragaria virginiana (FRVI, Virginia strawberry), and Potentilla gracilis (POGR, slender cinquefoil). Research was conducted during the summer growing season at two Oregon State University farms in Corvallis, OR in 2010 and 2011. The effects of glyphosate and dicamba alone, and in combination, were determined for simulated drift rates of 0.01 to 0.2 x field application rates (FAR) of 1119 g ha-1active ingredient (AI) for glyphosate and 560 g ha-1 AI for dicamba. Flowering phenology was rated by presence of buds (1), buds turning into flowers (2), flowers (3), flowers deteriorating and seeds beginning to form (4), and mature seeds (5); with data analyzed statistically for treatment (n=8 for each treatment) vs. control plots (n=8). Flowering patterns varied by species, farm and year; but, in general, herbicides alone or in combination reduced the number of plants with flowers on a sampling date and/or delayed the onset of full flowering for 3 species in 2010, and for 6 species in 2011. For example, the number of flowering plants was reduced with dicamba and/or glyphosate at 0.1 x FAR for ERLA and PRVU, with dicamba and/or glyphosate at 0.2 x FAR for CALE, with glyphosate at 0.1 x FAR for IRTE and RAOC, and with glyphosate at 0.2 x FAR for POGR. Results of this study provide evidence that herbicide drift can affect flowering phenology of native plants.