Evaluation of Di-Bak® Herbicide Capsule System for Control of Chinee Apple (Ziziphus mauritiana) in North Queensland

Abstract

Chinee apple (Ziziphus mauritiana Lam.) is a significant weed in the drier tropics of northern Queensland, Western Australia, and the Northern Territory. Throughout these regions its densely formed thickets influence the structure, function, and composition of rangeland ecosystems thereby outcompeting the native pasture species. The subsequent loss of pasture cover affects the quality of services (i.e., agronomic productivity, livestock carrying capacity, mustering, ecosystem services) obtainable from this diverse, natural resource. In Australia, the management of Z. mauritiana is limited to the application of synthetic herbicides and mechanical clearing operations. Whilst their efficacy is undisputed, there are concerns regarding the suitability of synthetic herbicides in ecologically sensitive or low-value habitats. This greater appreciation for environmental stewardship has promoted significant developments in the field of woody weed management.

This study investigates the effectiveness of a novel stem-implantation system for controlling woody weed species in grassland and rangeland environments. A pair of replicated trials were established among a naturally occurring population of Z. mauritiana at Alligator Creek, North Queensland (rural locality south of Townsville). The trials differed in dosage level by adjusting the application spacing (10 cm and 15 cm) of four encapsulated synthetic herbicides. An untreated control and benchmark treatment (drill-and-fill application of Tordon® RegrowthMaster) were also assessed for performance comparison. A significant effect (p <0.05) on plant vigor was discerned for both dosage levels within eight months of trial establishment. The highest incidence of mortality was observed among the individuals treated with aminopyralid + metsulfuron-methyl (37.5 mg/capsule and 30 mg/capsule), metsulfuron-methyl (330 mg/capsule) and picloram (1000 mg/capsule), achieving a similar response to the drill-and-fill application of Tordon® RegrowthMaster (200 g/L triclopyr, 100 g/L picloram and 25 g/L aminopyralid). We predict total mortality (~100%) with these preeminent treatments by the next assessment period (15 months), as well as equally effective control under a reduced dosage (by increasing spacing from 10 cm to 15 cm).