Stakeholders perspective of the economic cost of managing the invasive Navua sedge in tropical Queensland, Australia

Abstract

Weeds incur up to AUD $4 billion in economic loss annually to Australian agriculture. Despite this knowledge, there are few quantitative data on yield loss and control costs caused by weeds to the industry. Reported herein is the economic cost of managing the emerging, invasive Navua sedge weed to the grazing and cropping (sugarcane) industries of northern Queensland, Australia, following its introduction into the region in the 1970’s. Between 2020-2022, through a survey questionnaire given to impacted stakeholders (farmers), information relating to control cost, yield loss, and infestation history were documented. Collated data were analyzed using mainly non-parametric statistics due to the skewed and/or qualitative nature of many of the responses. Invasion history of the weed on farming properties is relatively recent (time: 10-20 yrs), and infestation level, though majorly and currently of low-medium status (median value: 22.5%), varies appreciably amongst properties. Median cost of managing Navua sedge was AU $72.91/hectare (AU $82.06 present value). This cost nor the type of management tactics (chemical vs. integrated weed management [IWM]) did not vary between land use types; however, the labor (relative to chemical and machinery) component of the control cost was the greatest. The currently approved herbicide, halosulfuron-methyl (SempraTM), is largely ineffective in controlling the weed due to its inability to deplete below-ground tubers of the weed. Correlation analyses suggest control costs will continue to increase with increasing Navua sedge infestation over time, especially in grazing lands. Farmers show high awareness of the challenge of managing the new weed incursion. Farmers are using myriads of strategies, including willingness to impose strict biosecurity measures and IWM tactics while waiting for more effective herbicides and promising biocontrol agents to minimize the spread and impact of the weed.