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

Abstract

Weeds causes up to $4 M economic loss to Australian agriculture alone. Despite this knowledge, there are only few quantitative analysis on industry economic losses caused by weeds. We report, the economic cost of the invasive Navua sedge (Cyperus aromaticus) to the agriculture industry. It is a monocot weed of the wet tropics of northern Queensland, Australia that was first documented in in the region in 1970s. In Northern QLD, numerous grazing and cropping (mainly sugar cane) sites, covering both coastal and upland landscapes are infested with Navua sedge. Through elicitation and survey questionnaire given to impacted stakeholders we obtained information relating to yield loss, control cost and infestation history. Data gathered between 2020-2024 suggested that Navua sedge incursion and observed impact on agriculture in the region is relatively recent (mean time: 15 yrs; range: 10-17 yrs), but infestation level varies significantly (P < 0.05) amongst sites (mean proportion of property infested: 34%; range: 20%-48%; and the mean property size: 162 hectares). Control cost averaged $75.37 per hectare; this cost did not vary between land use type. The current control cost per year per stakeholder is in the order: labour (mean: $6,800, range $1,500-$12,000); chemical usage (mean: $6,000, range $800-$11,000); machinery costs (mean: $4,300, range $1,600- $7,000). Correlation analyses suggest that farmers are willing to manage the weed infestation up to a threshold of 60%, above which many simply give up due to excessive control cost. The implication of size and time since infestation for optimal management of the weed at the farm and landscape levels are also discussed.