Location: Biological Control of Pests Research
2021 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
Final report, replaced by new project 6066-22000-093-000D, "Endemic Plant Pathogens for Biological Control of Invasive Aquatic and Terrestrial Weeds."
Research was conducted on the evaluation of a reduced mycotoxin formulation and mutant strains of Myrothecium verrucaria (MV) for control of kudzu and other invasive weeds. Researchers at the USDA-ARS Biological Control of Pests Research Unit, Stoneville, Mississippi, conducted controlled environment and field research on bioherbicidal control of kudzu with several concentrations of a mycelial Myrothecium verrucaria (MV) formulation combined with various rates of a glyphosate formulation (Touchdown), and found that almost complete kudzu control was achieved in field plots, conducted at two locations in Mississippi, even at combinations of the bioherbicide and the herbicide at the lowest rates tested.
Impact. This research indicates that an integrated control program involving cultural, herbicide/chemical interactions, and bioherbicide formulations may be required for successful kudzu control.
Bioherbicidal control of giant salvinia. Research was conducted for evaluation of a bioherbicidal fungus (Botryosphaeria rhodina, BR) for controlling giant salvinia in greenhouse and small field trials. Highly virulent, rapidly, and inexpensively produced mycelial formulations controlled 90-100% of weeds. Controlled-environment studies were established to determine the air temperatures for optimal infection and mortality of giant salvinia. Several surfactants were evaluated for their effect on improvement of weed control efficacy. Greenhouse experiments were conducted to determine the host range of BR. High virulence was found on giant salvinia under greenhouse and field conditions, and on common salvinia, red azolla, common duckweed, and alligator weed under greenhouse conditions. Little or no disease occurred on several common crop and plant species that occur where BR might be released for giant salvinia control. BR was also evaluated for both contact-based mortality and plant-quality mediated impact to the biological control insect agent Cyrtobagous salviniae. BR had little if any negative impact; only when mixed with a wetting agent did negative impacts occur and then these were minimal. A floating granule formulation was evaluated in greenhouse experiments. Greenhouse experiments were conducted to evaluate various inoculum concentrations of SPFG for bioherbicidal control of giant salvinia. 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. The new Project Plan will de-emphasize research on MV and will continue research on BR for controlling giant salvinia.
Accomplishments
1. Bioherbicides to control weeds. ARS researchers in 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. 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.
2. Biocontrol of problematic invasive aquatic weeds. Biocontrol of problematic invasive aquatic weeds. Common duckweed (Lemna minor) is a rapidly spreading aquatic plant that deprives ponds of oxygen and leads to the death of fish and beneficial algae in still waters. It is important to control duckweed for the health of ponds and existing aquatic life. It can be aggressive invaders of ponds and are often found mixed in with mosquito fern (Azolla caroliniana). ARS researchers in Stoneville, Mississippi, conducted experiments using an SPFG mycelial formulation and found that 95-100% mortality of these weeds was achieved within 48 hours following inoculation. These findings are important because in addition to being important invasive weed pests, some Azolla spp. have been shown to produce a neurotoxin [ß-Methylamino-L-alanine (BMAA)], a non-proteinogenic amino acid, generally thought to produced mainly by cyanobacteria.
3. Formulations to enhance bioherbicidal pathogen efficacy. Eastern black nightshade (Solanum ptycanthum) (EBN) is a problematic weed found throughout the eastern United States. ARS researchers in Stoneville, Mississippi, conducted greenhouse and field experiments to compare the effects of an invert (water - in - oil) emulsion (IE) versus a surfactant - water (water + Tween 80) spore formulations of a bioherbicidal fungus, Colletotrichum coccodes (Cc) for controlling this weed. Greenhouse tests revealed that several other economically important solanaceous weeds, including the exotic invasive weed tropical soda apple (S. viarum), were infected and killed at significantly greater levels by the fungus in the IE as compared to the surfactant formulation. Field tests revealed that >90% EBN control and dry weight reductions occurred when plants were treated with the fungus/IE formulation, while the fungus/surfactant formulation failed to control the weed. These results demonstrate that this invert emulsion formulation can promote the bioherbicidal efficacy of Cc, and also suggest its utility to improve the efficacy of other bioherbicides that may have been previously rejected for further development due to low efficacy or environmental constraints.
4. Biocontrol of invasive aquatic weeds. Giant salvinia, (Salvinia molesta) is an aquatic floating fern native to South America, but has become invasive in some areas in Africa, Asia, Australia, and in subtropical and warmer temperate areas of the United States. ARS researchers in Stoneville, Mississippi, and the U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi, conducted experiments using two species of Myrothecium (M. rodridum and M. verrucaria) to evaluate their bioherbicidal potential for control of this weed under outdoor conditions. Common duckweed (Lemna minor) is a rapidly spreading aquatic plant that deprives ponds of oxygen and leads to the death of fish and beneficial algae in still waters. It is important to control duckweed for the health of ponds and existing aquatic life. It can be aggressive invaders of ponds and are often found mixed in with mosquito fern (Azolla caroliniana). ARS researchers in Stoneville, Mississippi, conducted experiments using an SPFG mycelial formulation and found that 95-100% mortality of these weeds was achieved within 48 hours following inoculation. These findings are important because in addition to being important invasive weed pests, some Azolla spp. have been shown to produce a neurotoxin [ß-Methylamino-L-alanine (BMAA)], a non-proteinogenic amino acid, generally thought to produced mainly by cyanobacteria. The results indicated that some fungal formulations have the potential of being effective bioherbicides of giant salvinia, as they have shown to be effective in other weed systems.
