Invasive plants and agri-food waste extracts as sustainable alternatives for the pre-emergence urban weed control in Portugal Central Region

ABSTRACT The continued use of synthetic herbicides to control weeds leads to environmental pollution and health issues. Consequently, chemical formulations have been increasingly banned. However, sustainable solutions are lacking in the market. Alternatively, valorisation of phytotoxic waste to reduce the herbicides use promotes sustainability, meeting circular economy. We aimed at assessing the herbicidal potential of aqueous extracts of waste from the management of invasive plants (Acacia dealbata bark, Oxalis pes-caprae biomass) and agri-food (spent coffee grounds) on common urban weeds (Achillea ageratum, Conyza canadensis and Dittrichia viscosa) in Portugal. In vitro (paper and soil) and pot assays (soil) were conducted to test the pre-emergence (germination and seedlings) and post-emergence (well-stablished plants) effect of waste extracts on these weeds. Extracts reduced pre-emergence performance of weeds, but marginally affected post-emergence parameters. Germination was inhibited up to 83% by O. pes-caprae in A. ageratum, up to 88% and 87% by A. dealbata and O. pes-caprae in C. canadensis, and up to 70% by concentration in D. viscosa. A. dealbata and O. pes-caprae extracts also drastically reduced radicle length (30% and 55% in A. ageratum, 77% and 81% in C. canadensis, 90% and 92% in D. viscosa, respectively). However, soil neutralized the inhibitory pre-emergence effect. The main findings highlight that the use of A. dealbata and O. pes-caprae extracts as bioherbicides may require an additional synthetic herbicides application, as extracts alone cannot fully control urban weeds in areas without soil. Combining bioherbicides and commercial formulations still reduces the application of toxic chemicals, promoting sustainability.