Tolerance of Phalaris aquatica to spraytopping rates of glyphosate or paraquat

Abstract

The tolerance of a 7-year-old stand of Phalaris aquatica to spraytopping rates of paraquat (0.09, 0.14, 0.28 kg a.i./ha) and glyphosate (0.11, 0.16, 0.32 kg a.i./ha) applied on 17 October and 8 November 1988 was assessed over the following 9 months. In the first 28 days after spraying, the herbicides browned out most green leaf of P. aquatica; thereafter, plants fully or partially recovered. Nine months after spraying, ground cover of P. aquatica was reduced by all treatments (from 26 to 66%, relative to the controls) except the 3 rates of paraquat and the lowest rate of glyphosate applied in October. The greater effect of herbicides in November than in October was assessed as being due to more green leaf on P. aquatica at spraying and better growing conditions in November.