Simulated Herbicide Drift Alters Native Plant Flowering Phenology

Data for herbicide effects on plant flowering are needed to determine potential impacts on plant reproduction. Thus, flowering phenology was determined for up to 12 weeks after herbicide treatment for native Willamette Valley plants growing in small plots on two Oregon State University experimental farms. Six perennial species were evaluated: Camassia leichtlinii (CALE), Elymus glaucus (ELGL), Eriophyllum lanatum (ERLA), Festuca idahoensis subsp. roemeri (FEID), Iris tenax (IRTE), and Prunella vulgaris var. lanceolata (PRVU). Effects of glyphosate and dicamba, alone and in combination, were determined using simulated drift rates of 0.1 or 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. Flowering phenology was evaluated as stage of development on a scale from no buds (converted to 0), buds (1), pre-flowering (2), flowering (3), post-flowering (4), to mature seeds (5) before herbicide treatment and for 12 weeks after treatment. Flowering response to herbicides varied by species and farm; but, in general, dicamba and glyphosate resulted in earlier flowering stages (delayed or not full flowering) for the dicot ERLA, and to a lesser extent, PRVU; and glyphosate resulted in earlier flowering stages for the monocot IRTE. Based on these data, the concentration of herbicide affecting flowering stage was 0.1 x FAR. Once flowering stage was inhibited by dicamba and glyphosate, plants generally did not recover to full flowering. This study provided evidence that common herbicides can affect flowering phenology of native plants with implications for seed production.

Impact/Purpose

Just as reproductive effects are an important human toxicological response, effects on plant reproduction could have significant consequences for individual species and plant communities. Particularly of interest are effects on plant reproduction from herbicides, which are designed to adversely affect target weeds, and also possibly nontarget plants due to drift. Herbicide effects on plant flowering are an important potential ecological endpoint for risk assessments for herbicides, however, relevant field studies are limited. To address the need for data in this area, flowering, which is essential for sexual reproduction of plants, was evaluated for native Willamette Valley plant species growing together in small constructed communities (0.45 x 0.45 m plots) under field conditions on two Oregon State University farms. Flowering was evaluated for up to 12 weeks after herbicide treatment for perennial species: Camassia leichtlinii (CALE), Elymus glaucus (ELGL), Eriophyllum lanatum (ERLA), Festuca idahoensis subsp. roemeri (FEID), Iris tenax (IRTE), and Prunella vulgaris var. lanceolata (PRVU). Effects of the widely used herbicides glyphosate and dicamba were determined when applied alone and in combination, using simulated drift rates of 0.1 or 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. Flowering was evaluated visually using on a scale ranging from no buds (converted to 0), buds (1), preflowering (2), flowering (3), postflowering (4), to mature seeds (5). Flowering responses to the herbicides varied by species and farm; but, in general, dicamba and glyphosate reduced flowering of the broadleaf species ERLA, and to a lesser extent, PRVU; and also reduced flowering for the monocots CALE and IRTE. Based on these data, the concentration of herbicide affecting flowering was 0.1 x FAR. Once flowering was inhibited by herbicides, the plants did not recover. This study provided new evidence that common herbicides can affect flowering of native plants with implications for seed production and subsequent ecological impacts to be considered in non-target plant risk assessments.

Citation

Olszyk, D., T. Pfleeger, T. Shiroyama, M. Blakeley-Smith, E. Lee, M. Nash, AND M. Plocher. Simulated Herbicide Drift Alters Native Plant Flowering Phenology. Springer, New York, NY024-02795-3, (2024). [DOI: 10.1007/s10646-024-02795-3]

DOI: Simulated Herbicide Drift Alters Native Plant Flowering Phenology