Location: Biological Control of Pests Research
2019 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. Effects of SPFG on Cyrtobagous salviniae colonies and interaction research continued in laboratory and greenhouse. Field experiments continued in a giant salvinia-infested pond near Shreveport, Louisiana. A process was developed to enable the commercial bioherbicidal fungus, Colletotrichum gloeosporioides f. sp. aeschynomene (CGA) to simultaneously control northern jointvetch, Indian jointvetch, and hemp sesbania, three of the most economically important weeds in southern U.S. rice production. In greenhouse tests, CGA spores formulated in an invert emulsion or a surfactant (Silwet L-77) controlled all three weeds 98-100%. These results suggest that the host range of CGA can be expanded though formulation modification to enable this bioherbicide to control multiple weeds, thus improving its bioherbicidal marketing potential. A stable freeze-dried formulation of CGA was developed and was stable (viable) > 9 months after production. Studies were conducted to assess possible interactions of the herbicide glyphosate with Myrothecium verrucaria (Mv), a bioherbicide that can control several economically important weeds including Palmer amaranth. Glyphosate inhibits a key enzyme responsible for the biosynthesis of aromatic amino acids and compounds involved in plant defense, but the mode of action of Mv is unknown. Previous research showed that Mv, when combined with some commercial formulations of glyphosate, resulted in synergistic interactions on weed control, but some commercial glyphosate products were toxic to Mv. Greenhouse and laboratory studies showed that high purity glyphosate (without adjuvants/surfactants) was not inhibitory to Mv growth and sporulation at concentrations up to 2.0mm. Plants of both red and green biotypes were injured by Mv and Mv plus glyphosate treatments at 20 h after application. Injury effects increased through the 6-day time course, and at 120 h after treatment the plus glyphosate treatment resulted in 100% mortality of all glyphosate-susceptible and -resistant plants. The interaction of glyphosate plus Mv was found to be synergistic for Palmer amaranth control. Data suggest that glyphosate (not formulation additives) is responsible for the synergy found when this bioherbicide is combined with some commercial formulations of glyphosate.
Accomplishments
1. Biocontrol of problematic invasive aquatic weeds. Mosquito fern (Azolla caroliniana) a member of the Salviniaceae is an aquatic floating fern native to warmer temperate areas of the U.S. Scientists at USDA-ARS in Stoneville, Mississippi, conducted experiments using an SPFG mycelial formulation and found that 100% mortality of this weed was achieved within 48 h following inoculation. This is important because in addition to being an important invasive weed pest, some Azolla spp. have recently been shown to produce the neurotoxin ß-Methylamino-L-alanine (BMAA), a non-proteinogenic amino acid, generally thought to produced mainly by cyanobacteria.
Review Publications
Hoagland, R.E., Boyette, C.D., Jordan, R.H., Stetina, K.C. 2018. Interaction of the bioherbicide Myrothecium verrucaria with technical-grade glyphosate on glyphosate-susceptible and -resistant Palmer amaranth. American Journal of Plant Sciences. 9:2306-2319.
Hoagland, R.E., Boyette, C.D., Jordan, R.H., Stetina, K.C. 2018. Interaction of glufosinate and Colletotrichum truncatum on ammonia levels and glutamine synthetase activity in Hemp sesbania. American Journal of Plant Sciences. 9:2320-2337.
Boyette, C.D., Hoagland, R.E., Stetina, K.C. 2018. Hot water treatment enhances the bioherbicidal efficacy of a fungus. American Journal of Plant Sciences. 9(10):2063-2076.
Boyette, C.D., Hoagland, R.E., Stetina, K.C. 2019. Extending the host range of the bioherbicidal fungus Colletotrichum gloeosporioides f. sp. aeschynomene. Biocontrol Science and Technology. 29(7):720-726.
