Thinning Jarrah with Hormone Herbicides

Abstract

SUMMARY Experiments to test the effect of herbicides, and methods of application, on jarrah (Eucalyptus marginata Sm.) poles are described. The treatment ‘plots’ in the experiments consisted of sets of individual stems selected at random from the study area. The translocation of herbicides via naturally-fused root systems was found to be of little significance in field operations provided care is taken to regulate the dosage rate of herbicide. The relative efficiency of a wide range of herbicides is discussed, picloram proving the most efficient of those tested to date. The reaction of jarrah to herbicide injections includes the formation of epicormic shoots due to rapid kill of the crown, and the promotion of leaf abscission by sub-lethal doses of picloram and 2,4,5-T. Effective herbicide dosage rates appear to lead to the inhibition of leaf abscission. The experiments have led to the adoption of hormones in non-commercial thinnings. Current practice in thinning jarrah is to inject 2.5ml of a 1 to 4 dilu...