The use of glyphosate for the management of secondary coppice regrowth in a Eucalyptus grandis × E. urophylla coppice stand in Zululand, South Africa

Abstract

In South Africa, commercial eucalypt stands may be regenerated through the stepwise reduction of coppice shoots following felling. The development of secondary coppice regrowth following these reduction operations results in competition with the remaining stems, possibly resulting in a reduction in growth. Currently, secondary coppice regrowth is controlled manually, or through spraying with glyphosate at 0.6% when ca. 0.75 m in height. No research has been conducted to determine whether alternative rates and/or timing of application are possible or cost-effective. In 2006 a trial was implemented in Zululand, South Africa on a recently coppiced stand of Eucalyptus grandis × Eucalyptus urophylla so as to optimise rates of glyphosate application (0.6%, 1.2% and 1.8%) for the control of secondary coppice regrowth at various heights (0.5, 1.0 and 1.5 m). Tree and secondary coppice regrowth variates were measured annually until rotation-end (9 years, 3 months). The volume of herbicide used, the number of occasions each treatment was sprayed and associated costs were combined to provide an indication of the most cost-effective treatment. Although there were no significant differences in final coppice yield for the various rates of glyphosate and timing of application (as assessed by the size of the secondary coppice regrowth) tested, treatment efficacy in terms of treating secondary coppice regrowth increased with an increase in the rate of glypho- sate applied (0% < 0.6% < 1.2% < 1.8%), especially when treated at either 1.0 or 1.5 m in height. The use of glypho- sate, irrespective of rate and/or timing of application (as assessed by secondary coppice regrowth height), proved to be more cost-effective compared with manual control or the spraying of the secondary coppice regrowth at 0.75 m height with 0.6% glyphosate. The most cost-effective treatment was 1.2% glyphosate applied when the secondary coppice regrowth was 1.5 m. If reduced herbicide use is a major criterion within a company portfolio, then the secondary coppice regrowth can be manually removed when 1.5 m.