The use of wood vinegar as a non-synthetic herbicide for control of broadleaf weeds

Pruning trees in urban landscapes produces a large amount of pruning waste. Pyrolysis is a process that thermally converts lignocellulosic biomass to a number of useful products, including wood vinegar. The objectives of this research were to 1) identify the composition and property of wood vinegar resulting from the pyrolysis of elm (Ulmus spp.) tree pruning waste and 2) evaluate the efficacy of wood vinegar for control of several broadleaf weed species. Acids along with various other chemical groups including alcohols, aldehydes, carbohydrates, phenols, nitrides, and ketones were identified in wood vinegar. Water constituted the highest proportion of wood vinegar, accounted for 77 % by weight. In growth chamber experiments, wood vinegar at 4000 L ha−1 showed 95 % injury and 76 % fresh aboveground biomass reduction of perilla mint [Perilla frutescens (L.) Britt.] compared to the nontreated control at 7 d after treatment, whereas a 2000 L ha-1 application volume caused 80 % injury, with 60 % biomass reduction. The efficacy of 1000 or 2000 L ha−1 application volume were significantly lower. In field experiments, wood vinegar showed varying levels of control for perilla mint, creeping woodsorrel (Oxalis corniculata L.), and Carolina geranium (Geranium carolinianum L.). While wood vinegar at 4000 L ha-1 provided 100 % control of perilla mint and control of creeping woodsorrel and Carolina geranium were 82 % at best. Further, faster and greater control was achieved at low temperatures (10 °C) compared with high temperature conditions (20 or 30 °C). Overall, these findings suggest that wood vinegar derived from the pyrolysis of pruning waste can be used as a non-synthetic herbicide for control of broadleaf weeds.