The economic cost of managing Navua sedge (Cyperus aromaticus) - a monocot weed of tropical Queensland, Australia

Abstract

Weeds incur yearly up to $4 Billion economic loss to Australia agriculture. Despite this knowledge, quantitative data on yield loss and control cost caused by weeds to the industry are few. We report herein, the economic cost of managing the invasive Navua sedge (Cyperus aromaticus) to the grazing and cropping (sugarcane) industries of northern Queensland, Australia. Navua sedge, was first documented in the wet tropical region of northern Queensland in 1970s, and now appear to be spreading fast and impacting negatively on both conservation and agricultural landscapes. Between 2020-2023, through elicitation and survey questionnaire given to impacted stakeholders (farmers), information relating to control (labour, chemical and machinery) cost, yield loss, and infestation history were documented. Invasion history is recent (mean time: 15 yrs; 95% CI range: 10-22 yrs), and infestation level varies significantly amongst properties (mean proportion of individual property infested: 30.8%; CI range: 15-46%; mean property size: 767.84 acres, range: 341-1193 acres). Cost of managing Navua sedge averaged $80 per hectare ($32.60 per acre), translating to $89/hectare ($36.02/acre) present value. This cost did not vary between land use types (grazing vs. cropping); however, the labour component (compared to chemical and machinery) of the control cost was the greatest, especially in the grazing industry. Correlation analyses suggest control cost will continue to increase with increasing levels of Navua sedge infestation over time, especially in grazing lands. Farmers show willingness to impose strict biosecurity measures and practice integrated weed management tactics while waiting for promising biocontrol agents to minimize the spread and impact of the weed.