Prolonging glyphosate effectiveness on difficult to control summer weeds.

Heavy reliance on glyphosate in conservation farming systems has resulted in the prevalence of certain weed species favoured by its over use. If the effectiveness of glyphosate on these weeds continues to decline, the sustainability of these systems will be impacted adversely. This study aims to determine effective ways to improve control of the problem weeds: fleabane, barnyard grass and sweet summer grass without increasing their glyphosate tolerance or resistance. The double knock tactic was investigated for its effectiveness in controlling these species and preventing seed-set. Results showed that following glyphosate and glyphosate mixes with either paraquat + diquat or paraquat provided highly effective control (up to 100%) of these species. Fleabane control was reduced as the interval for the follow-up application increased beyond 14 days. This study has shown that sequential knockdown treatments are effective in controlling glyphosate tolerant weeds, potentially preventing herbicide resistance evolution and thus prolonging the effectiveness of glyphosate.