The effects of paraquat and glyphosate residues in sprayed herbage on the development of seedlings of a normal and a paraquat-tolerant variety of Lolium perenne

Paraquat and glyphosate were sprayed on to simulated swards in a glasshouse experiment. Residues of these herbicides depressed emergence, growth and survival of Lolium perenne seedlings sown after spraying. Residues of paraquat applied at a rate (1·5 kg ha‐1) within the range normally used for sward destruction killed nearly all seedlings of a normal L. perenne variety, Barlenna, but had much less effect on the paraquat‐tolerant variety, Causeway. It was estimated that Causeway was almost nine times as tolerant of paraquat residues as Barlenna. Sowing at a depth of 20 mm gave some protection against paraquat residues. A delay of 10 d between spraying and sowing had equivocal effects. It was concluded that residues of paraquat used for killing swards before direct drilling may hinder the establishment of normal L. perenne varieties but not of paraquat‐tolerant varieties. Residues of glyphosate had equal effects on the two varieties and the effects were severest on seedlings sown on the soil surface immediately after spraying. It is thought to be unlikely that glyphosate residues in sprayed herbage would be a problem in direct drilling.