Optimisation of a Stem-Implanted Herbicide Capsule System for Effective Management of Chinee Apple (Ziziphus mauritiana)

Abstract

There has been a recent appreciation for “sustainability” and environmental stewardship within the agricultural industry driven by concerns of herbicide-resistance, unbalanced ecosystems, and food security. This has underscored the urgency for more novel solutions in weed management, with a particular focus on the reduced reliance of synthetic herbicides. In the last decade, a proprietary stem-implantation system has been developed for the encapsulated delivery of a fungal bioherbicide in parkinsonia (Parkinsonia aculeata). This technology has since expanded to the targeted, readily calibrated application of synthetic dry-formulations in several other woody weed species. More recently, a preliminary study investigated the compatibility of this technology for the management of Chinee apple (Ziziphus mauritiana Lam.) in rangeland environments. Although this research only “scratched the surface”, there were two synthetic formulations identified (330 mg/capsule metsulfuron-methyl and 1000 mg/capsule picloram) for further evaluation under field conditions. A replicated trial (n = 315) was established among a naturally-occurring population of Z. mauritiana near Mulgrave, northern Queensland to explore (i) the potential synergism of the two efficacious synthetic herbicides (i.e., combined formulation), and (ii) the placement of the capsules themselves. Each of three synthetic treatments (i.e., metsulfuron-methyl, picloram, and the combination herbicide) were applied at the very base of the stem and approximately one metre from ground-level. There was a significant effect (p <0.05) on plant vigour for all treatments relative to the untreated control within twelve months of trial establishment. The highest incidence of mortality (>90% of treated plants) was observed among the encapsulated synthetic formulations delivered at the stem base. Theoretically, these compounds are more likely to be translocated downwards to the root system of the target species under the closest placement to ground-level. There was no significant differences (p >0.05) in the performance of the three synthetic formulations themselves at this optimised height of application.