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

Abstract

A field trial was set up to simulate a field margin environment to analyze sub-lethal effects of the herbicide metsulfuron-methyl on several endpoints of non-target terrestrial plants (NTTPs). Both vegetative and reproductive endpoints were evaluated. The experiment was conducted in an experimentally established field strip with sown species. The treatments consisted of five dosages and a control: 0, 0.0097, 0.0193, 0.058, 0.174, and 0.348 gram active ingredient per hectare (g a.i./ha). The plant cover, number of (flowering) individuals per species and fruit collection were performed and estimated weekly for a period of 4 months. At the end of the growing season, the total dry biomass per species was obtained and the collected fruits were weighed, counted, and sieved to obtain the seeds. The seeds were counted and weighed as well, before they were used in a germination experiment to test the seed emergence of the F1 generation. The herbicide only affected the biomass of Matricaria recutita at the treatment levels tested (0.058 g a.i./ha and higher). Field dosages of 0.174 and 0.348 g a.i./ha differed significantly in the endpoint "plant cover" compared to lower dosages and controls. The F1 generations of Sinapis alba, Centaurea cyanus, and Phacelia tanacetifolia were particularly affected at field dosages of 0.0193 g a.i./ha and higher, showing significantly lower seed germination rates. This would imply that spray drift of metsulfuron-methyl might lead to shifts in species compositions and succession in vegetation in off-crop areas adjacent to arable fields. Conducting germination experiments is necessary to investigate a herbicide's effect on the full life cycle of plants.

Comparative Assessment of Vegetative and Reproductive Terrestrial Plant Species Endpoints from Exposure to Herbicides and Potential Environmental Implications: A Review

“…(Plant performance was never significantly different from the controls, though, which illustrates how variable field data may be and how difficult if not impossible it would be to detect, e.g., 10% or 25% effect in the field.) Nelemans et al () found significant differences only between lower test rates with increases (hormesis) and higher rates with distinct reductions, but none between treatments and controls: The control plants performed better than those treated with the highest rate, but those with the lowest rate performed best, and only the differences between the extremes were significant. No precise ER50s were calculated for the reproductive endpoints in Nelemans et al () due to only weak dose–response and large scatter.…”

“…Nelemans et al () found significant differences only between lower test rates with increases (hormesis) and higher rates with distinct reductions, but none between treatments and controls: The control plants performed better than those treated with the highest rate, but those with the lowest rate performed best, and only the differences between the extremes were significant. No precise ER50s were calculated for the reproductive endpoints in Nelemans et al () due to only weak dose–response and large scatter. Based on Figures 3A and 3C in Nelemans et al (), the lowest ER50 (germination F1) must be around 0.05 g/ha ( S. alba, Phacelia tanacetifolia ), so this reproductive endpoint is actually very close to the vegetative laboratory endpoint that drives the Tier‐1 RA for metsulfuron‐methyl ( S. alba : 0.054 g/ha, from EFSA ).…”

“…Nelemans et al () tested effects of metsulfuron‐methyl on NTTPs in the field and found that various endpoints, including seedling emergence of the F1 generation, were more affected than the vegetative endpoint assessed (plant cover, total aboveground biomass in the field, i.e., “at herbicide dosages of 0.0193 g a.i. [active ingredient] per hectare and higher”).…”

“…Finally there is some information indicating that the growth stage at which the plant is exposed may play an important role (e.g., Boutin and Rogers ; Gilreath and Chase ; Gilreath et al ; Strandberg et al ; Griffin et al ). For our separate investigation of the effect the application timing may have on the sensitivity, see Supplemental Data H, which also includes data from Bohnenblust et al (), Nelemans et al (), and Olszyk et al ().…”

“…The endpoint "F-1-germination" was also affected but was found to be considerably less sensitive (by an order of magnitude) than the other reproductive endpoint reported, "number of seeds per gram fresh weight" (Riemens et al 2009). Nelemans et al (2017) tested effects of metsulfuronmethyl on NTTPs in the field and found that various endpoints, including seedling emergence of the F1 generation, were more affected than the vegetative endpoint assessed (plant cover, total aboveground biomass in the field, i.e., "at herbicide dosages of 0.0193 g a.i. [active ingredient] per hectare and higher").…”