Activity of Ailanthus altissima (Mill.) Swingle Extract as a Potential Bioherbicide for Sustainable Weed Management in Horticulture

The sustainable management of weeds is one of the main challenges in agriculture. Recent studies have demonstrated the potential of plant phytotoxins, such as ailanthone fromAilanthus altissima(Mill) Swingle, as bioherbicides. Since a complex extract may be more active than a single compound, we explored the phytotoxicity ofA. altissimaextracts obtained from the leaves, samaras, rachises, and secondary roots, and we evaluated their application potential for weed control in horticulture. The pre-emergence activity of all plant extracts was evaluated over varying concentrations on two indicator species (i.e.,Lepidium sativumL. andRaphanus sativusL.) under controlled conditions. As the leaf extract was able to be generated in sufficient quantities, it was therefore further evaluated in glasshouse experiments with seven common weed species as indicators, as well as in a nursery production system for the cultivation of three horticultural crops (i.e.,Salvia officinalisL.,S. rosmarinusSchleid., andDianthus caryophyllusL.). Following the application of the extract, the index of germination (IGe%), the index of biomass, and the density of weeds per pot were evaluated, along with the impact on crop growth and quality (i.e., plant growth index and leaf damage). Under controlled conditions, the extract from the secondary root was the most active in reducing the IGe%, with greater persistence across time in both indicator species. At 18 days following application, the lowest concentration of the leaf extract at 1.8 mg L(-1)ailanthone reduced the IGe%by up to 15% and 45% inR. sativusandL. sativum, respectively. InR. sativus, all of the extract types affected the IGe%, but extract activity was greater inL. sativum. Under glasshouse conditions, leaf extracts containing 50 and 200 mg L(-1)ailanthone showed strong inhibition (98%-99%) in the biomass of all treated indicator and weed species. Under nursery conditions, leaf extracts formulated at 100 and 200 mg L(-1)ailanthone performed similarly, and no weeds were observed in any of the treated pots ofS. officinalisandS. rosmarinusin the 60-day study period. Conversely, in theD. caryophylluspots, an increase in the percentage of weed presence per pot was observed after 40 days. A reduction in the growth index and an increase in leaf phytotoxicity were observed during the cultivation experimentation, especially inS. officinaliswhen the extract was applied post-emergence to the crop canopy. Phytotoxicity was alleviated by the