Location: Biological Control of Pests Research
2017 Annual Report
Objectives
Objective 1. Improve the efficacy, environmental safety, and stability of two bioherbicides currently in development, SPFG and Myrothecium verrucaria (Mv), for the management of salvinia and kudzu, respectively.
Sub-objective 1.1. Develop safe, efficacious and stable formulations of the bioherbicide SPFG, and determine how interactions with insect herbivores can affect efficacy.
Sub-objective 1.2. Reduce or eliminate Mv mycotoxin levels while maintaining high product efficacy.
Approach
The research plan has two goals. The first will focus on evaluating and developing a fungal pathogen (referred to as ‘SPFG’ for proprietary purposes) for managing the exotic, invasive aquatic weed, giant salvinia (Salvinia molesta). The second deals with further developing and testing the fungus Myrothecium verrucaria (Mv) for controlling kudzu (Pueraria lobata var. montana) and other invasive weeds. Because Mv spores produce trichothecene mycotoxins, EPA registration has been hindered. A mycelial formulation devoid of, or with extremely low levels of mycotoxins should result in more likelihood for EPA registration. The development of effective bioherbicide formulations will be guided by the ecology of the pest target and an understanding of biotic and abiotic factors that influence the effectiveness of the bioherbicide. Formulations will be developed to compliment the surface chemistry of the pest host and bioherbicide for better attachment and infectivity, as well as to mitigate deleterious environmental factors that reduce or inhibit host-plant infection. The development of commercially-viable microbial pesticides for weeds could provide growers, land managers and homeowners with safe, cost-effective, non-chemical control tools for use in agriculture, chemically-sensitive environments, and natural ecosystems.
Progress Report
Research continued for evaluation of a bioherbicidal fungus (called SPFG in this report) for controlling giant salvinia in greenhouse and small field trials. Controlled-environment studies continued to define the air temperatures for optimal infection and mortality of giant salvinia. Various surfactants and surfactant concentrations were evaluated for their effect on improvement of giant salvinia control efficacy. A floating popcorn granular formulation was evaluated in greenhouse experiments. Greenhouse experiments were completed to determine the host range of SPFG and to evaluate various inoculum concentrations of SPFG for bioherbicidal control of giant salvinia. Highly virulent, rapidly and inexpensively produced mycelial formulations controlled 90-100% of weeds. Viable freeze-dried formulations of SPFG and Myrothecium verrucaria (Mv) mycelium were mass-produced and stored, demonstrating shelf-life of at least 6 months for SPFG and 9 years for Mv. Research continued on the evaluation of a reduced mycotoxin formulation and mutant strains of Mv for control of kudzu and other invasive weeds. Comparative studies were conducted on mycelial preparations of Mv and a recently discovered sector (Mv-Sector BSH) of this fungus. The whitish sector was discovered, isolated, grown in pure culture on PDA (Potato Dextrose Agar) and found to be a stable, non-spore producing mutant when cultured over several months under conditions that cause circadian sporulation during growth of its Mv parent. Application of Mv and the Mv sector mycelial preparations to intact plants (hemp sesbania and sicklepod) and leaf discs (kudzu and glyphosate-resistant Palmer amaranth) showed that the sector efficacy was generally equal to, or slightly lower than Mv.
Accomplishments
1. Efficacy improvement of bioherbicides via formulation. Bioherbicides can offer an effective alternative control strategy to chemical herbicides, but must be properly formulated in order to maximize effectiveness. USDA-ARS researchers in Stoneville, Mississippi, demonstrated that a strain of the fungus Colletotrichum (C.) coccodes isolated from eastern black nightshade was effective in controlling this weed under sub-optimal free-moisture (dew) conditions when fungal spores were formulated in an invert emulsion. These results demonstrate that formulating C. coccodes spores in an invert emulsion greatly improves the bioherbicidal potential of this fungus. Furthermore, results suggest that this formulation may render pathogens previously rejected for development as bioherbicides due to restrictive dew requirements more efficacious for use in controlling their target weeds.
2. Bioherbicides to control weeds. ARS scientists at Stoneville, Mississippi, evaluated phytopathogenic fungi as bioherbicides. Research continued on the evaluation of a reduced mycotoxin formulation of Myrothecium verrucaria (Mv) and mutant strains of Mv for control of kudzu and other invasive weeds. Comparative studies on mycelial preparations of Mv and a recently discovered sector (Mv-Sector BSH) of this fungus were carried out. The whitish sector was isolated and grown in pure culture on potato dextrose agar and found to be a stable, non-spore producing mutant when cultured over several months under conditions that cause circadian sporulation during growth of its Mv parent. Application of Mv and Mv-Sector BSH mycelial preparations to intact weed seedlings (hemp sesbania and sicklepod) and leaf discs of weeds (kudzu and glyphosate-resistant Palmer amaranth) showed that the sector efficacy was generally equal to, or slightly lower than Mv. Results indicate that certain bioherbicides have utility in controlling herbicide-resistant and recalcitrant weeds.
Review Publications
Boyette, C.D., Hoagland, R.E., Stetina, K.C. 2016. Efficacy improvement of a bioherbicidal fungus using a formulation-based approach. American Journal of Plant Sciences. 7:2349-2358.
Hoagland, R.E., Boyette, C.D., Stetina, K.C., Jordan, R.H. 2016. Bioherbicidal efficacy of a Myrothecium verrucaria-sector on several plant species. American Journal of Plant Sciences. 7:2376-2389.
Hoagland, R.E., Boyette, C.D. 2016. Controlling herbicide-susceptible, -tolerant and -resistant weeds with microbial bioherbicides. Outlooks on Pest Management. 27:256-266.
