Potential of a Black Walnut (Juglans nigra) Extract Product (NatureCur (R)) as a Pre- and Post-Emergence Bioherbicide

Black walnut (Juglans nigra) is known to have allelopathic effects on other plants. If extracts from black walnut can be commercially formulated as a bioherbicide, they may become an important weed-management tool for organic farming systems or areas where synthetic herbicides are not allowed. The toxicity of several concentrations of a black walnut extract-based commercial product (NatureCur (R)) was evaluated on seeds and seedlings of several weed species in the laboratory, greenhouse, and in an orchard. Petri dish experiments showed that the LD50 of NatureCur solution concentration for horseweed (Conyza canadensis) and hairy fleabane (Conyza bonariensis) seeds was 14.3 and 12.5%, respectively. However, the LD50 of the extract for common purslane (Portulaca oleraceae) and tall annual morninglory (Ipomoea purpurea) seeds was 20.5% and 20.9%, respectively. Weed seedlings grown in pots in the greenhouse were inhibited when 15 ml of the solution with a concentration of 33.3% was applied as a soil-drench. Micro-plot experiments in the orchard showed that application of 1 L of the solution with a concentration of 42.9% killed all the natural population of horseweed seedlings when applied as a soil-drench. This formulation of black walnut extract has potential as a pre- and post-emergent herbicide. The product, however, has not yet been registered as a pesticide and efficient methods of applying the material in the field need to be developed for commercial acceptance of this product as an organic herbicide.