The effect of spray adjuvants on the phytotoxicity of herbicides

Abstract

Greenhouse and field experiments were conducted on the tolerance of wheat (Tritiaum aestivum L.), barley (Hordeum sativum Jess.), rapeseed (Brassiaa napus L.) and flax (Linum usitatissimum L.) to selected nonionic surfactants (Triton XA, Wex and Renex 36) when applied with herbicides. In the greenhouse there were no significant differences in dry matter yield between plants treated with a herbicide plus additional nonionic surfactant in a tank-mix, and those treated with the herbicide alone for all cases where the herbicide already contained surfactants in its formulation. The effect of additional surfactant in a tank-mix with selected herbicides applied to flax and rapeseed was similar whether the plants were irrigated or were kept under water stress. Under field conditions there were no decreases in seed yield of barley, wheat, rapeseed and flax, when additional surfactants were included in a tank-mix with several different herbicides applied postemergence. There were no deleterious effects on wheat tolerance in situations where there was an overlapping of herbicide sprays to which Wex and Renex 36 had been added. Triton XA in a tank-mix with glyphosate [N-(phosphonomethyl)glycine] significantly reduced the herbicide activity on wheat plants. Ammonium sulphate significantly increased the activity of glyphosate in a number of greenhouse and field experiments. This activation occurred in distilled, Saskatoon city supply and Dundurn well water. In a greenhouse experiment glyphosate was significantly more effective when sprayed in distilled water than in city water. Glyphosate activity was considerably reduced in well water of very high mineral content but the activity could be restored and even enhanced with the addition of ammonium sulphate at the rate of 2.8 kg/ha. Agral 90 did not enhance the activity of glyphosate in this hard water, showing that the reduction of glyphosate activity in hard water was not due to reduced wettability. Activation of glyphosate by ammonium sulphate also occurred when the two compounds were applied sequentially, with ammonium sulphate being applied either 24 hours before or after the glyphosate treatment.