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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Improvement of Bioherbicide Strategies for Invasive Weeds in Southern Cropping Systems

Location: Biological Control of Pests Research Unit

2011 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).


3.Progress Report
A fungus (Fusarium oxysporum sp.) was isolated from the invasive tree mimosa that is highly effective against troublesome weedy tree species. This fungus does not apparently produce undesireable mycotoxins and was also found to be effective against kudzu in greenhouse experiments. The fungus can be easily produced on several inexpensive solid and liquid media, and may provide residual control against weedy species as well as other weedy leguminous weeds. Research continued on developing and evaluating a reduced mycotoxin Myrothecium (M.) verrucaria mycelial formulation. This formulation is efficacious against target weeds (kudzu, redvine, trumpetcreeper, hemp sesbania) when co-applied with a surfactant. Research has been focused on the surfactant Silwet L-77, but it is possible that more widely-available and less-toxic surfactants might be used instead. Five commercial products and 1 family of experimental compounds have been identified by ARS researchers at Stoneville, MS, that improve the activity of this fungus. In greenhouse trials, some of these products achieved the same bioherbicidal activity as Silwet L-77 even when applied with only 20% as much of the bioherbicide.

Field plot research on herbicidal control of kudzu has been evaluated at two locations for three years. Two classes of herbicides have constantly produced excellent control of kudzu. In the fourth year of the study treatments transitioned from broadcast applications to spot treatments to achieve eradication. Observations revealed that mowing kudzu can provide greater than 50% suppression, even in the year after treatment. Subsequent work has demonstrated greater than 90% control with a combination of mowing, bioherbicide and herbicide application. This work has fostered collaboration with the Mississippi Department of Transportation, private landowners and the Holly Springs National Forest. A new experimental herbicide is under evaluation in replicated field trials.

Work was completed in field experiments in which trumpetcreeper and redvine were successfully controlled by two applications (fall and spring) of M. verrucara mycelium combined with a compatible herbicide glyphosate commercial formulation (Touchdown). A single application of either Touchdown alone, the fungus alone, or the fungus in combination with glyphosate did not control either weed species. The fact that the fungus is capable of controlling several different weeds in addition to kudzu improves the utility and potential marketability of this bioherbicide.


4.Accomplishments
1. New bioherbicide formulations. Although herbicides are usually effective in controlling most weeds, there are weeds, such as mimosa, that are not effectively controlled by herbicides. Bioherbicides may offer an effective alternative control strategy, but must be properly formulated in order to maximize effectiveness. Researchers at the USDA-ARS Biological Control of Pests Research Unit, Stoneville, MS, isolated a fungus (Fusarium oxysporum sp.) from the invasive tree mimosa that is highly effective against this troublesome weedy tree species. This fungus apparently does not produce undesireable mycotoxins, and was found to be effective against kudzu in greenhouse experiments. The fungus can be readily produced on several inexpensive solid and liquid media, and may provide residual control against these weedy species, as well as other weedy leguminous weeds. Research continues on developing and evaluating a reduced mycotoxin Myreothecium (M.) verrucaria mycelial formulation. This formulation is efficacious against target weeds (kudzu, redvine, trumpetcreeper, hemp sesbania) when co-applied with a surfactant. Research has been focused on the surfactant Silwet L-77, but it is possible that more widely-available and less-toxic surfactants might be used instead. Five commercial products and 1 family of experimental compounds have been identified by ARS researchers at Stoneville, MS, that improve the activity of this fungus. In greenhouse trials, some of these products achieved the same bioherbicidal activity as Silwet L-77 even when applied with only 20% as much of the bioherbicide. The newly discovered pathogen Fusarium sp. may prove to be a valuable tool for controlling several invasive woody species. The further demonstration that toxin production by this fungus can be greatly reduced using appropriate culturing and growth media modification has enabled large scale, off-site field testing, and interest by EPA and commercial entities.

2. Kudzu control. 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 herbicidal control of kudzu, which has been evaluated at two locations for three years. Two classes of herbicides have constantly produced excellent control of kudzu. In the fourth year of the study we are transitioning from broadcast applications to spot treatments to achieve eradication. Observations revealed that mowing kudzu can provide greater than 50% suppression, even in the year after treatment. Subsequent work has demonstrated greater than 90% control with a combination of mowing, bioherbicide and herbicide application. This work has fostered collaboration with the Mississippi Department of Transportation, private landowners and the Holly Springs National Forest. A new experimental herbicide is under evaluation in replicated field trials.

3. Redvine and trumpetcreeper control. Redvine and trumpetcreeper are invasive weedy vines and are highly tolerant to many commercial herbicides, such as glyphosate. Because they are not effectively controlled by herbicides, they are becoming more widespread in many 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, completed three-year field experiments in which they found that trumpetcreeper and redvine were successfully controlled by two applications (fall and spring) of Myrothecium (M.) verrucara mycelium combined with a compatible herbicide glyphosate commercial formulation (Touchdown). A single application of either Touchdown alone, the fungus alone, or the fungus in combination with glyphosate did not control either weed species. The fact that the fungus is capable of controlling several different weeds in addition to kudzu improves the utility and potential marketability of this bioherbicide.


Review Publications
Hoagland, R.E., Mccallister, T.S., Boyette, C.D., Weaver, M.A., Beecham, R.V. 2011. Effects of Myrothecium verrucaria on morning-glory (Ipomoea) species. Allelopathy Journal. 27(2):151-162.

Boyette, C.D., Hoagland, R.E. 2010. Biological control of hemp sesbania (Sebania exaltata) and sicklepod (Senna obtusifolia) in soybean with anthracnose pathogen mixtures). Weed Technology. 24:551-556.

Bowling, A.J., Vaughn, K.C., Hoagland, R.E., Stetina, K.C., Boyette, C.D. 2010. Immunohistochemical investigation of the necrotropic phase of the Fungus colletotrichum geoeosporioides in the biocontrol of Hemp sesbania (Sesbania exaltata; Papilionaceae). American Journal of Botany. 97(12):1-12.

Last Modified: 8/21/2014
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