Impact of glyphosate drift on non-target field margin invertebrates

Abstract

Grassy arable field margins provide important permanent habitats for arthropods in agroecosystems and due to their proximity to high input areas, are exposed to pesticide drift. The aims of this thesis are to determine the likely effects of glyphosate drift in arable field margins by examining patterns of a medium quality spray drift intercepted by plant species in buffer strips and the effects of glyphosate on non-target field margin arthropods. Levels of mediumquality spray drift, analogous to herbicide drift, intercepted by field margin plant species in field boundaries were significantly reduced by inclusions of 2m and 6m wide buffer strips. Levels of spray drift interception varied between plant species and were related to plant height and leaf area. Dose-response testing of glyphosate against field margin plant species was done to establish inherent susceptibilities to the herbicide. Many species appeared to be unaffected by high levels of glyphosate (1800g ha-1), while others had relatively high ED50s that were unlikely to be exceeded by UK recommended rates of glyphosate. It was noted that lack of exposure to interspecific competition may have enhanced the plant species tolerance to high levels of glyphosate. Different rates of glyphosate were screened against the non-target arthropods Lepthyphantes tenuis (Araneae) and Leptopterna dolabrata (Heteroptera) to assess toxicity. Glyphosate was found to be non-toxic, however, applications of glyphosate to food plants increased mortality in L. dolahrata. In a field experiment, glyphosate applications of more than 360g ha-1 to a grassy arable field margin reduced Araneae, Heteroptera and Carabidae abundance. Community analyses (DCA) indicated that communities in the field margins exposed to more than 360g ha-1 glyphosate were distinct from unsprayed field margins. It is predicted that drift of field applied glyphosate at rates greater than 1440g ha-1 would reduce phytophagous Heteroptera and Gonalium rubens (Araneae) abundance.