Weed management is generally viewed as a major challenge in conventional, transitional and organic cropping systems. Natural product herbicides have the potential to play an important role on organic farms by reducing reliance on tillage and cultivation and by replacing expensive hand weeding operations. On the other hand, cost effective natural products with high efficacy could replace more toxic pesticides currently in use on conventional farms. One of the current problems in today's agriculture is the development of herbicide resistance among weeds, particularly among biotypes of rice weeds such as early and late watergrass. Natural product herbicides with novel chemistries can potentially offer a solution for resistance management, particularly if their efficacy is based on new modes of action. The research proposed here is focusing on the development of efficacious natural product herbicides based on microbial metabolites and other natural products. More specifically, we are proposing the development of a microbial bioherbicide which combines a strain of actinomycetes (Streptomyces sp.) isolated from marine sources with another synergistic natural product compound. The secondary metabolite from the herbicidal Streptomyces strain, thaxtomin A, has in preliminary tests shown good herbicidal activity as well as selectivity for rice. The research proposed here will evaluate the herbicidal efficacy and phytotoxicity of microbial thaxtomin A when used in combination with other active compounds produced by microbes or derived from plant extracts against the most common rice weeds in the US. Part of this project will focus on determination of mechanism of action for novel herbicidal compounds obtained in the applicant's in-house screening program. Preliminary bioassays on some of the novel herbicidal compounds have shown good efficacy against grass weeds, which suggests that they could be used in combination with thaxtomin A to enhance its efficacy against grass weeds in rice cultivations. The results from the Phase I research will help assess the commercial potential of these new bioherbicides, especially the one selective for rice. The results indicating low toxicity, economical production, and good efficacy support the registration of these novel products as biopesticides for use in both conventional and organic farming. We expect that these new biocontrol products would first be used for organic production but due to increased demand for new herbicidal products for resistance management, they will also benefit conventional farms looking for new pesticides with low toxicity and new modes of action.
