2012 Annual Report
1a.Objectives (from AD-416):
The objective of the proposed research is to improve the methods of production, formulation and delivery of indigenous pathogens to safely and effectively control invasive weeds. Kudzu (Pueraria lobata var. montana) and old-world climbing fern (Lygodium microphyllum) are not well controlled by chemical herbicides and are often present in sensitive areas where herbicides may be inappropriate. Other aggressive weeds, such as marestail (Conyza canadensis) and pigweeds (Amaranthus spp.) are commonly found to be resistant to the popular herbicide, glyphosate. This research plan is designed to develop safe, affordable, and practical control strategies for these weeds using the fungal plant pathogen, Myrothecium verrucaria and combinations of M. verrucaria, other weed pathogens and compatible chemical herbicides and adjuvants.
The overall objective of this project is to develop and improve biological weed control with plant pathogens (bioherbicides). Our research will focus on the following objectives:
Objective 1: Develop safe and effective formulation, mass-production, and application technology techniques and systems to improve the bioherbicidal potential and utility of bioherbicides for controlling exotic, invasive or glyphosate-resistant weeds.
Objective 2: Bioherbicidal and integrated control of kudzu.
1b.Approach (from AD-416):
The research plan comprehensively addresses bioherbicide development from cost-effective production methods to exclude unwanted byproducts and; to optimize formulations of bioherbicides with respect to spore and leaf-surface hydrophobicity and maintenance of free-moisture; to deliver bioherbicides with maximum spray coverage; and post-release monitoring of the agroecosystem documenting the persistence and spread of biocontrol agents. Production methods will be monitored by liquid chromatography to detect unwanted byproducts. Plant bioassays with visual and digital disease ratings will assess the effectiveness of bioherbicide formulations. Field tests will be performed in mature, naturally-occurring kudzu stands to validate bioherbicide efficacy alongside benchmark herbicides. DNA-based species-specific markers will be identified to enable post-release monitoring of bioherbicides. A strain of the bacterial pathogen Xanthomonas campestris and reduced mycotoxin formulations for biological control of glyphosate-resistant weeds such as marestail (Conyza campestris) and pigweeds (Amaranthus spp).
A strain of the bacterium Xanthomonas campestris was shown to be effective in controlling common cocklebur, monosodiummethylarsenate (MSMA)-resistant cocklebur, and glyphosate-resistant marestail in greenhouse experiments. A fungus (Fusarium oxysporum f. sp. perniciosum) (FSP) isolated from mimosa was found to be highly efficacious against this troublesome invasive weedy tree. FSP does not produce undesirable mycotoxins, and was also found to be effective against kudzu in greenhouse experiments, and it can be readily mass-produced on several inexpensive solid and liquid media. FSP may provide residual control against these weedy species as well as other weedy leguminous weeds. Research continued on developing and evaluating a reduced mycotoxin Myrothecium verrucaria (MV) mycelial formulation. This formulation is efficacious against several target weeds (kudzu, redvine, trumpetcreeper, hemp sesbania and sicklepod), as well as glyphosate-resistant pigweeds and marestail in corn, when co-applied with a surfactant as a directed spray. Field plot research continued on bioherbicidal control of kudzu with MV at two locations over four years. Granular formulations (‘Pesta’) of MV suppressed kudzu and hemp sesbania significantly. Several morningglory spp. were controlled efficaciously by MV in greenhouse experiments, while trumpetcreeper and redvine were successfully controlled by two applications (fall and spring) of MV mycelium combined with a compatible glyphosate herbicide commercial formulation (Touchdown). A single application of either Touchdown alone, or the fungus alone, did not control either weed species.
Biological control of weedy trees. Weedy tree species are becoming increasingly problematic in highway rights-of-ways and natural areas. A fungus (Fusarium oxysporum f. sp. perniciosum), isolated from the invasive tree mimosa by researchers at the USDA-ARS Biocontrol of Pests Research Unit, Stoneville, MS, was shown to be highly effective against this troublesome weedy tree species. This fungus does not produce undesirable mycotoxins, and is also effective against kudzu in greenhouse experiments.
Improvement of bioherbicide formulations. Undesirable secondary metabolites that are produced by many fungi may hinder their commercialization potential. Research continued on developing and evaluating a reduced mycotoxin Myrothecium verrucaria (MV) mycelial formulation. This formulation is efficacious against kudzu, redvine, trumpetcreeper, hemp sesbania, and glyphosate-resistant pigweeds and marestail. The further demonstration that toxin production by this fungus can be mitigated using appropriate culturing and growth media modification has enabled large scale, off-site field testing, and interest by Evironmental Protection Agency (EPA) and commercial entities has resulted. This research may yield insight resulting in methodology to eliminate these mycotoxins, thus making MV and similar organisms more feasible for commercialization.
Biological control of kudzu. Kudzu continues to be a serious, rapidly spreading invasive weed threat. Effective control measures are needed, such as improved chemical, biological, and chemical-biological interactions for optimal weed control. Researchers at the USDA-ARS Biological Control of Pests Research Unit, Stoneville, MS, conducted field plot research on bioherbicidal control of kudzu with Myrothecium verrucaria (MV) formulations, at two locations for four years, and have demonstrated greater than 90% control of kudzu is achieved through a combination of mowing, bioherbicide and herbicide application. Granular formulations (such as ‘Pesta’ or other novel formulations) of Myrothecium verrucaria also effectively suppressed kudzu growth and spread. This research indicates that an integrated control program involving cultural, bioherbicide/chemical interactions, and bioherbicide formulations may be required for successful kudzu control.
Biological control of weedy vines. Weedy vines are becoming increasingly problematic in southern U.S. row crop production. Redvine, trumpetcreeper, and morningglories are invasive weedy vines, and are tolerant to many commercial herbicides, such as glyphosate. Because these weeds are not effectively controlled by herbicides, they are becoming more widespread in many genetically modified organisms (GMO) crops, such as Roundup-ready soybeans; clearly, more effective control measures are required for these weeds. Researchers at the USDA-ARS Biological Control of Pests Research Unit, Stoneville, MS, found that trumpetcreeper and redvine were successfully controlled by two applications (fall and spring) of Myrothecium verrucaria (MV) mycelium combined with a compatible herbicide glyphosate commercial formulation (Touchdown). A single application of either the herbicide alone, MV alone, or MV in combination with glyphosate did not control either weed species. MV also controlled several morningglory species in greenhouse experiments. The fact that MV is capable of controlling several different weeds in addition to kudzu, improves the utility and potential marketability of this bioherbicide.
Biological control of glyphosate-resistant weeds. Although herbicides are usually effective in controlling most weeds, there are weeds that are either not effectively controlled by herbicides, or have developed resistance to certain classes of herbicides. Bioherbicides may offer an effective alternative control strategy, but must be properly formulated in order to maximize effectiveness. A strain of the bacterium Xanthomonas campestris, isolated from cocklebur by researchers at the USDA-ARS Biological Control of Pests Research Unit, Stoneville, MS, was shown to be effective in controlling common cocklebur and glyphosate resistant marestail in greenhouse experiments. This pathogen can be readily produced on several inexpensive solid and liquid media, and may provide effective control against these weedy species as well as other related weeds.
Boyette, C.D., Hoagland, R.E., Weaver, M.A., Stetina, K.C. 2012. Biological control potential of Colletotrichum gloeosporioides for coffee senna (Cassia occidentalis). American Journal of Plant Sciences. 3:430-436.
Boyette, C.D., Gealy, D.R., Hoagland, R.E., Vaughn, K.C., Bowling, A.J. 2012. Hemp Sesbania (Sesbania exaltata) control in rice (Oryza sativa) with the bioherbicidal fungus Colletotrichum gloeosporioides f. sp. aeschynomene formulated in an invert emulsion. Biocontrol Science and Technology. 21 (12):1399-1407.
Boyette, C.D., Bryson, C.T., Hoagland, R.E., Weaver, M.A. 2012. Effects of simulated rainfall on disease development and weed control of the bioherbicidal fungi Alternaria cassiae and Colletotrichum truncatum. Weed Technology. 26:117-121. DOI: 10.1614/WT-D-10-00127.1.
Boyette, C.D., and Hoagland, R.E. 2012. Interactions of chemical additives, pH, and temperature on Conidia germination and virulence of Colletotrichum truncatum, a bioherbicide of Sesbania exaltata. Allelopathy Journal. 30:103-116.
Weaver, M.A., Boyette, C.D., Hoagland, R.E. 2012. Bioherbicidal activity from washed spores of Mycrothecium verrucaria. World Journal of Microbiology and Biotechnology. 28:1941-1946.