ASHS 2025 Conference

Specialty and organic crop weed management strategies are challenging due to limited chemical control products with good efficacy that are cost effective. The need for new bioherbicide modes of action has become increasingly urgent in modern agriculture as most bioherbicides have nonspecific modes of action with no systemic activity. Introducing new bioherbicides that are also registered as organic is essential to diversify weed control strategies. By fostering innovations in bioherbicide development agricultural systems can be more environmentally friendly by preserving ecosystems while maintaining the ability to feed a growing global population. Manuka oil is derived from the leaves and branches of the Manuka tree (Leptospermum scoparium) and contains β-triketones. The β-triketone rich fraction contains leptospermone that inhibits a key enzyme, p-hydroxyphenylpyruvate dioxygenase (HPPD). This process directly inhibits carotenoid biosynthesis, upstream in the biochemical pathway, which causes damage to the photosynthetic apparatus and leads to bleaching of the leaf tissue which eventually kills the plant. There were three studies that examined the efficacy of β-triketone extract against Lolium multiflorum, Amaranthus retroflexus, and Abutilon theophrasti. The studies were 1) pre-emergence β-triketone extract ranging from 0 to 2.5 mg ml-1, 2) post-emergence β-triketone extract ranging from 0 to 6%, and 3) post-emergence β-triketone extract at 0.5 and 2.0% with five different organic adjuvants. In the pre-emergence study, there were significant differences between the β-triketone extract treatments and 100% weed control down to 0.625 mg ml-1. In the post-emergence study, there was significant decreases in weed height and fresh and dry mass when compared to the control treatment. However, the adjuvants did not have any effect on weed height and fresh and dry mass. Thus, there is significant evidence that commercializing a water soluble β-triketones enriched extract of Manuka oil can be an effective weed control, especially as a pre-emergent bioherbicide for specialty and organic crop production.