Testing pelargonic acid and pyraflufen-ethyl with glyphosate as alternatives to paraquat dichloride for the preparation of fire-break tracer lines at Underberg, South Africa

Over the past 31-year period, about 18 700 ha annum ⁻¹ of planted forests in South Africa have been lost through fire. In forested areas where the risk of fire entering compartments is always high, fire-break tracer lines are prepared by spraying with a suitable herbicide such that the adjacent vegetation is still 'green' when these tracer lines can be burned. Once the vegetation between these tracer lines has dried out sufficiently, the intervening areas can safely be burned. Up until 2012, paraquat dichloride (1,1′-dimethyl-4,4′-bipyridinium ion) was used for the preparation of these tracer lines, but due to it being listed as a highly hazardous pesticide, it can no longer be considered. As a first screening trial, Guild (pyraflufen-ethyl + glyphosate) and Scythe (pelargonic acid) were tested in April 2012 at various rates for the preparation of tracer lines in the Underberg region, together with a control (no treatment), paraquat (the then current herbicide of choice) and glyphosate. The percentage live vegetation cover was determined two weeks after treatment initiation to assess herbicide efficacy, and again in early summer (seven months) to assess vegetation recovery. Relative to the control, paraquat was the most effective herbicide in terms of both initial control, as well as vegetation recovery. With the exception of Guild (at 0.5 l ha ⁻¹), the other herbicides at the rates tested either did not provide effective initial control of the vegetation or they killed the vegetation such that recovery was poor. Of all the alternative products/rates tested, Guild at 0.5 l ha ⁻¹ was the only treatment that gave reasonable initial control (59.8% relative to the control), together with excellent recovery (81.3% relative to the control). If Guild were to be considered, further testing in terms of rates and timing of application is needed to confirm these findings and to refine its potential for use.