Relative tolerance of Microlaena stipoides to glyphosate herbicide

Abstract

Microlaena stipoides (meadow rice grass, weeping grass, pātītī) is a native grass of Australasia and Malesia and is reputed to have a high degree of tolerance to the herbicide glyphosate. We conducted a glyphosate application rate experiment on a set of 3m ? 3m plots covered with a mixed sward including Microlaena as a component, using rates varying from 0 – 8 L ha-1 equivalent of the product G Force Max? (54% glyphosate formulation) applied in May 2009. Foliage damage assessments over the following 8 weeks indicated that Microlaena was more tolerant of the herbicide than Pennisetum clandestinum (kikuyu) and Agrostis capillaris (browntop), with mean damage levels of 63% at 2 L ha-1, a level which killed all other species in the plots. At 8 L ha-1, damage to Microlaena at 8 weeks was highly variable, with a mean of 77%. Species cover assessments conducted in late February 2009 (pre-spray) and March 2010 (post-spray) showed that all three major sward components declined in cover at all herbicide rates over that year. However, for Microlaena there was no difference between the rates in terms of the magnitude of the decline, in contrast to kikuyu and browntop, which both had greater declines at higher herbicide rates. We conclude that it is possible to use low rates of glyphosate in autumn to discriminate in favour of Microlaena in a mixed grass sward.