Submitted to: Journal of Toxicology Toxins Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 6, 2007
Publication Date: November 30, 2007
Citation: Hoagland, R.E., Boyette, C.D., Weaver, M.A., Abbas, H.K. 2007. Bioherbicides: Research and Risks. Journal of Toxicology Toxins Reviews. 26:313-342. Interpretive Summary: Weeds are one of the most costly and limiting factors in crop production. Over the past four decades, synthetic herbicides have dominated weed management strategies, and have accounted for nearly 60% of the total agricultural pesticides used in the U. S. The high costs involved in developing and registering herbicides, plus recent trends in environmental awareness concerning pesticides, have prompted investigations for alternative systems of weed control, such as biological control with bioherbicides. Some advantages of bioherbicides over traditional chemical herbicides are: specificity for the target weed, absence of adverse effects on humans, wildlife or domestic animals, rapid degradation, and low risk of residues in surface or ground water, crops, soil or food chains. However in some instances, there may be concerns or disadvantages regarding the development and use of bioherbicides. Certain bioherbicidal organisms produce secondary metabolites that exhibit deleterious effects towards mammalian systems and the environment. This could be of major concern when such microbes are used in an augmentative manner. There are several intrinsic limitations common to nearly all biological agents, that must be overcome before these agents become widely acceptable. This chapter presents an overview of bioherbicides with emphasis on factors related to risk, registration, and potential commercialization. Special emphasis is placed on a potential bioherbicide, Myrothecium verrucaria, its associated risks, and an outline of our future research that may reduce or eliminate the risk factors (mycotoxin production) of this fungal pathogen.
Technical Abstract: Riparian buffer zones are highly productive ecotones, critical in protecting downstream systems from upstream sources of nutrients, pesticides, and sediments. Soil properties, enzyme activities, microbial fatty acid profiles and plant species composition were assessed at four transects in a forested riparian zone between cropland and Beasley Lake, in Sunflower County, Mississippi. This riparian corridor spans several gradients: from a heavily wooded, typical bottomland hardwood forest above the channel, to an open-area assemblage of annual and perennial, facultative hydrophytic vegetation lower in the system. The soils in this system form a gradient with more sand and less clay (mean = 18% sand, 39% clay) on the forested banks compared to the channel (mean = 7% sand, 59% clay). Coinciding with differences in vegetation, hydrology and soil type exhibited significant differences in microbial community structure and activity. Fluorescein diacetate hydrolysis and triphenyl tetrazolium chloride dehydrogenase activities were positively associated with each other and with clay content, but did not vary with stream or slope position. The microbial community, as assessed by Fatty Acid Methyl Esters (FAME), responded significantly to slope position, sampling date and soil textural components, but not to stream position (upstream vs. downstream). The interactions between vegetation, soil properties and the microbial community are being studied to better understand their cumulative roles in contaminant removal by riparian zones.