Impact of glyphosate drift on non-target field margin invertebrates.
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"), 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' glyphosate were distinct from unsprayed field
margins. It is predicted that drift of field applied glyphosate at rates greater than 1440g ha"
would reduce phytophagous Heteroptera and Gonalium rubens (Araneae) abundance.