Sublethal effects of the herbicide glufosinate ammonium on crops and wild plants: short-term effects compared to vegetative recovery and plant reproduction

Abstract

Current guidelines for phytotoxicity testing rely heavily on short-term testing of primarily crop species to predict the sensitivity of non-target, wild plants to herbicides. However, little is known on how plants recover following initial growth inhibitions in standard 14-28 day greenhouse tests conducted for pesticide assessment and registration. The objectives of this study were to assess the ability of plant species to recover (biomass and reproduction) when tested at the juvenile stage (routine regulatory testing), comparing crop and wild species and using the herbicide glufosinate ammonium. Ten crops and 10 wild species were tested with a one-time exposure to glufosinate ammonium in a greenhouse. Half the plants of each species (9 doses × 6 replicates) were harvested 3 weeks after being sprayed (short-term). The remaining plants were harvested several weeks later, coinciding with seed set or natural senescence (long-term). Total aboveground biomass and several endpoints related to crop production and plant reproduction were measured. Calculated IC50 values (dosage that results in a 50% decrease in the biomass of a plant as compared to the untreated controls) based solely on aboveground biomass, for species harvested in the long-term were generally higher than those obtained in the short-term (with two exceptions), indicating recovery over time. Crop species did not differ from wild species in terms of sensitivity. However, in seven out of 12 cases where reproduction was measurable, reproductive endpoints were more sensitive than either short or long-term biomass endpoints, indicating the importance of examining these parameters in phytotoxicity testing. Glufosinate ammonium was found to be phytotoxic at low doses (2.64-7.74% g ai/ha of the label rate).

Effects of the Herbicide Metsulfuron-Methyl on a Plant Community, Including Seed Germination Success in the F1 Generation

“…In addition, an NOED of 0.058 g a.i./ha was found in weeks 6 and 7, while an NOED of 0.348 g a.i./ha was found in week 8. This difference suggests that plants can recover from spraying, as was also found in other studies (de Snoo et al, 2005;Carpenter and Boutin, 2010;Strandberg et al, 2012;Schmitz et al, 2014). In comparison with lower-level treatments, plots with dosages of 0.174 and 0.348 g a.i./ha featured more grasses (Poaceae), as we found through visual observation.…”

“…The lack of statistical differences can be explained by the low number of observations, which also varied between the plots, reducing the power of the statistical tests. Other studies have demonstrated that reproductive endpoints are indeed very sensitive to metsulfuron-methyl Blackburn and Boutin, 2003;Olszyk et al, 2004;Kjaer et al, 2006;Carpenter and Boutin, 2010;Pfleeger et al, 2012;Schmitz et al, 2014Schmitz et al, , 2015. Our results also showed hormesis occurring in S. alba, P. tanacetifolia and C. cyanus, at low dosages of metsulfuron-methyl and in both vegetative and reproductive endpoints.…”

“…For example, in the field study by Kjaer et al (2006), exposure of Hawthorn (Crateaegus monogyna) to metsulfuron-methyl resulted in 100% losses of berries at a field application rate of 0.05 g a.i./ha, while the vegetative endpoints (leaves) remained unaffected. Findings of other studies Blackburn and Boutin, 2003;Olszyk et al, 2004;Carpenter and Boutin, 2010;Pfleeger et al, 2012;EFSA PPR Panel, 2014;Schmitz et al, 2014Schmitz et al, , 2015 also suggest that reproductive endpoints are more sensitive than vegetative endpoints, especially in comparison with biomass as a vegetative endpoint.…”

Winter wheat yield loss in response to Avena fatua competition and effect of reduced herbicide dose rates on seed production of this species

“…Several studies could show that seed production is often more reduced by herbicides compared to weed biomass [24,25,26,27]. The presented results suggest that this is only true for A. fatua under high crop competition.…”

Scientific Opinion on good modelling practice in the context of mechanistic effect models for risk assessment of plant protection products

“…Species related to the crops for which a specific herbicide is intended for use usually have a higher tolerance to that herbicide (White and Boutin, 2007). Several studies conducted in Canada and Denmark have shown that there is no significant difference between the sensitivity of short-and long-lived species (Boutin et al, 2004;Carpenter and Boutin, 2010;Strandberg et al, 2012). Therefore, it is not possible at this stage to propose one species which is generally more sensitive to toxicants.…”