Pelargonic acid for the management of firebreak tracer-lines: results from four trials implemented in South Africa

Abstract

Most South African planted forests occur in high wildfire risk regions, with firebreaks used to minimise the risk of run-away fires. Desiccant herbicides together with burning are used for firebreak preparation in a stepwise manner. In late summer, 1–2 m wide tracer-lines are sprayed on either side of the proposed firebreak. Once desiccated, the vegetation in the tracer-lines is burned, with the green vegetation remaining between the tracer-lines and outside of the firebreak preventing the spread of fire. In autumn, following the seasonally induced die-back of vegetation (due to frosts and reduced rainfall), the vegetation remaining between these tracer-lines is burned, thus creating a larger buffer (firebreak), free from combustible material for the management of unplanned fires. To test the efficacy of pelargonic acid as a replacement for paraquat (highly hazardous due to acute toxicity and high bioaccumulation), four trials were implemented. In addition to a no-spray control and the use of paraquat (current standard), different rates of pelargonic acid (6/8/10%) with, or without ammonium sulfate were tested to determine the most robust treatment across different vegetation types. Glufosinate-ammonium was included for comparative purposes. Paraquat resulted in the highest degree of desiccation 7–8 days after application, with glufosinate-ammonium being the least effective. Desiccation was further increased at higher rates of pelargonic acid application (10 > 8 > 6%), with glufosinate-ammonium improving desiccation further. Pelargonic acid applied at 10% with the addition of ammonium-sulphate was most similar to that of paraquat.