Influence of adjuvants on tetrapion efficacy for nassella tussock (Stipa trichotoma Nees) control and subsequent seedling establishment: a preliminary study

Abstract

Nassella tussock (Stipa trichotoma Nees) is a perennial grass weed that seeds prolifically, resulting in build-up of a large soil seed bank. Due to it's vigorous growth it has the potential to spread rapidly in disturbed environments and overgrazed areas. Field trials were initiated in a dense nassella tussock infestation to assess the influence of various adjuvants (Citowett, Frigate and Reverseal 9) on the herbicide activity of tetrapion (sodium 2, 2, 3, 3-tetrafluoropropion) and to monitor subsequent seedling establishment. Reverseal 9 was the only adjuvant that significantly increased the efficacy of tetrapion at 0.44kg ai ha1, but this level of control achieved (75%) was not considered adequate for large-scale nassella tussock control operations. The next higher rate of tetrapion (0.88 kg ai ha1) was effective in achieving nearly total mortality (98%) with or without the addition of Reverseal 9. This rate also restricted establishment of nassella tussock seedlings for up to 23 months after initial application. Further studies with tetrapion/Reverseal 9 combinations are recommended in an attempt to reduce the current registration rate of tetrapion (0.88kg ai HEN), thereby saving costs and reducing the negative impact on desirable grasses and subsequent veld rehabilitation.