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United States Department of Agriculture

Agricultural Research Service

2007 Annual Report

1a.Objectives (from AD-416)
Discover, develop, and improve augmentative bioherbicides, as viable weed biocontrol products through innovative field application, formulation, and mass-production strategies. Develop methodologies to eliminate, reduce or regulate undesirable secondary metabolites from biocontrol pathogens. Discover disease-promoting or weed defense-inhibiting chemicals that synergize bioherbicide. Identify or create biocontrol pathogens with novel traits. Develop molecular markers for bioherbicide strain identification, post-release monitoring, and environmental risk assessment. Discover novel information on genetic determinants and regulation mechanisms of pathogenicity, e.g., virulence, stability, host range and phytotoxin production.

1b.Approach (from AD-416)
Assess biocontrol potential of several pathogens for control of various weeds: Myrothecium verrucaria for kudzu, redvine, and trumpetcreeper, Colletotrichum truncatum for hemp sesbania, and C. gloeosprioides cassiae for sicklepod. Assess formulations, interactions with agrochemicals, and application timing under field conditions. Assess combinations of host-specific bioherbicides to broaden the weed control spectrum. Develop methodologies for mass production and formulation to improve stability and virulence of bioherbicides. Reduce or eliminate undesirable secondary metabolites (e.g. trichothecenes) from M. verrucaria through mutagenesis, fermentation modifications, growth media alterations, strain selection, use of metabolic regulators, purification, and filtration of pathogen cultures. Inhibitors and other methods to metabolically inactivate trichothecene synthesis in M. verrucaria will be examined. Monitor toxin production via HPLC, ELISA, and HPLC-MS. Assay plant tissues from laboratory, greenhouse and field tests to determine enzyme and secondary plant constituent levels related to weed defense mechanisms against pathogens. Implement biochemical analyses of biomarker defense enzymes and plant constituents to ascertain mechanism of action of the pathogen and the synergistic action of combination of herbicides and other compounds with pathogens. Develop molecular methods for strain identification and post-release monitoring during field testing. Assess the ecological competence of biocontrol agents and the influence of environmental and weed host factors in field and controlled model systems.

3.Progress Report

We have discovered an isolate of Myrothecium verrucaria (MV) that is very efficacious against kudzu and other invasive weeds, and this pathogen is the primary focus of our biological control of weeds research efforts. This strain of M. verrucaria produces a group of mycotoxins that may limit its practical usage. Several industrial entities have expressed interest in developing this pathogen commercially if mycotoxin content can be reduced to levels acceptable by Environmental Protection Agency (EPA). We have developed methodologies to reduce MV mycotoxin content to a level of EPA. acceptability for registration.

The fungus Colletotrichum gloeosporioides, originally isolated from the weed species, coffee senna, can effectively control a related weed, sicklepod, when fungal spores are formulated in either unrefined corn oil or an invert emulsion. Control of hemp sesbania is also enhanced when fungal spores are applied to weeds in an unrefined corn oil emulsion. We are also currently evaluating MV formulations with reduced trichothecene content that we have developed, and have demonstrated that these formulations retain high weed control efficacy.

Redvine and trumpetcreeper are increasingly problematic in no-till and low-till soybeans in the Mississippi Delta, and are highly tolerant to recommended glyphosate usage rates. We have found that sequential applications of a glyphosate product, followed by an application of MV, will effectively control these weeds. Control of kudzu and other highly invasive weeds may require a combination of management practices. Identifying the ability to co-apply MV with newer herbicides provides greater ability for use of the bioherbicide. We have also discovered a synergistic interaction occurs between certain glyphosate products and Colleototrichum truncatum for improved biological control of hemp sesbania.

Laboratory studies have assessed the compatibility of MV with three herbicides currently being used for control of kudzu: aminopyralid (Milestone), metsulfuron (Escort) and flouoroxypyr (Vista). A good degree of survival of spores was found in tank mix concentrations of Milestone and Escort and was capable of growth in the presence of commercial formulation of these herbicides. Field trials are evaluating efficacy of combinations of the biocontrol fungus with these herbicides for integrated kudzu control.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of non-peer reviewed presentations and proceedings6
Number of newspaper articles and other presentations for non-science audiences7

Review Publications
Boyette, C.D., Jackson, M.A., Bryson, C.T., Hoagland, R.E., Connick Jr, W.J., Daigle, D.J. 2006. Sesbania exaltata biocontrol with Colletotrichum truncatum microsclerotia formulated in ‘Pesta’ granules. Biocontrol. DOI 10.1007/s10526-006-9031-7.

Boyette, C.D., Hoagland, R.E., Weaver, M.A. 2007. Biocontrol efficacy of Colletotrichum truncatum for hemp sesbania (Sesbania exaltata) is enhanced with unrefined corn oil and surfactant. Weed Biology and Management. 7:70-76. doi:10.1111/j.1445-6664.2006.00230.x.

Hoagland, R.E., Weaver, M.A., Boyette, C.D. 2007. Myrothecium verrucaria fungus: A Bioherbicide and Strategies to Reduce Its Non-Target Risks. Allelopathy Journal 19(1): 179-192.

Williams, R.D., Hoagland, R.E. 2007. Phytotoxicity of mimosine and albizziine on seed germination and seedling growth of crops and weeds. Allelopathy Journal. 19(2):423-430.

Boyette, C.D., Reddy, K.N., Hoagland, R.E. 2006. Glyphosate and bioherbicide interaction for controlling kudzu (Pueraria lobata), redvine (Brunnichia ovata), and trumpetcreeper (Campsis radicans). Biocontrol Science and Technology. 16(10):1067-1077. DOI: 10.1080/09583150600828742.

Boyette, C.D., Hoagland, R.E., Abbas, H.K. 2007. Evaluation of the bioherbicide Myrothecium verrucaria for weed control in tomato (Lycopersicon esculentum). Biocontrol Science and Technology. 17(2):171-178. DOI: 10.1080/09583150600937451.

Lovelace, M.L., Talbert, R.E., Scherder, E.F., Hoagland, R.E. 2007. Effects of multiple applications of simulated quinclorac drift rates on tomato. Weed Science 55:167-169.

Weaver, M.A., Lyn, M.E. 2007. Compatability of a Biological Control Agent with Herbicides for Control of Invasive Plant Species. Natural Areas Journal 26:264-268.

Last Modified: 11/27/2015
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