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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "absorption"

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    ItemOpen Access
    Herbicide absorption and translocation by Eurasian watermilfoil and hydrilla
    (Colorado State University. Libraries, 2012) Vassios, Joseph D., author; Nissen, Scott, advisor; Westra, Philip, committee member; Shaner, Dale, committee member; Meiman, Paul, committee member
    Hydrilla and Eurasian watermilfoil are submersed invasive species that occur commonly across the US. These species are aggressive competitors, and form dense, monotypic stands. Dense stands of these species form mats on the surface, and impact water flow, as well as the economic and ecological value of water bodies. With the severe impact of these species, many control methods have been implemented to restore value to infested areas. The systemic herbicides fluridone, penoxsulam, and triclopyr are registered for aquatic use. While all three herbicides can be used for Eurasian watermilfoil control, only fluridone and penoxsulam can be used for hydrilla. The rates and selectivity for these herbicides have been documented, but little work has been completed to characterize their absorption and translocation in submersed aquatic species. The goals of this research were to (1) evaluate herbicide absorption and translocation following shoot exposure, (2) evaluate herbicide absorption and translocation following root exposure, and (3) evaluate triclopyr absorption and translocation in Eurasian watermilfoil following liquid and granular treatments. Previous work established linear relationships between herbicide lipophilicity (as determined by log KOW) and bioaccumulation in both terrestrial and aquatic species. Based on the differences in lipophilicity among the three herbicides tested (fluridone>>penoxsulam>triclopyr) we expected fluridone to accumulate the most in these species, with significantly lower accumulation of penoxsulam and triclopyr. Bioaccumulation following root exposure followed this trend, with significantly greater fluridone accumulation than penoxsulam or triclopyr; however, following shoot exposure, triclopyr accumulation was greatest in both species 192 HAT, followed by fluridone and penoxsulam. Overall accumulation was similar for both species following root exposure, but accumulation following shoot exposure was approximately three times greater for Eurasian watermilfoil. Translocation was limited following both root and shoot exposures. The translocation following root treatment was greater than shoot treatment in nearly all cases, with up to 27% of absorbed herbicide present in shoots 192 HAT. Translocation following shoot treatment showed a maximum of 12.5% of absorbed herbicide present in roots 192 HAT. These findings are consistent with previous work that indicated there was more acropetal than basipetal translocation in submersed species. There were no significant differences in overall absorption by Eurasian watermilfoil following liquid and granular triclopyr treatments; however, differences were observed between plant parts. Apical meristems accumulated the most triclopyr following liquid treatment, and root accumulation was greatest following granular treatment. Distribution at the whole plant level resulted in 11 times more herbicide in roots following granular treatment when compared to the liquid treatment. These results indicate that granular formulations may provide better control of Eurasian watermilfoil roots, compared to an equal rate of a liquid formulation.
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    ItemOpen Access
    Understanding aminocyclopyrachlor behavior in soil and plants
    (Colorado State University. Libraries, 2012) Lindenmayer, Richard Bradley, author; Westra, Philip, advisor; Nissen, Scott, committee member; Shaner, Dale, committee member; Hansen, Neil, committee member
    Many noxious and invasive weeds are perennial species that are inherently difficult to control. Canada thistle (Cirsium arvense) and field bindweed (Convolvulus arevensis) are two species of particular interest as they are capable of spreading quite rapidly through creeping underground reproductive structures and are able to continually regenerate from carbohydrate reserves stored in the roots. These weed species infest both cropland and non-cropland, including rangeland, pasture, natural areas, and rights-of-way, causing yield loss in crops from competition for soil resources and by harboring crop insect and disease pests as well as reducing ecosystem diversity in natural areas by displacing desirable or native vegetation with monocultures. Based on long-term weed control observed in the field with aminocyclopyrachlor (Lindenmayer et al. 2009), a better understanding of the herbicide's behavior in soil as well as within the plants was necessary. The objectives of this research were to (1) compare soil and foliar activity of aminocyclopyrachlor on Canada thistle to that of aminopyralid; (2) determine the dissipation rates of aminocyclopyrachlor, aminopyralid, and clopyralid under field conditions as well as evaluate their adsorption in six North American soils; and (3) evaluate aminocyclopyrachlor absorption, translocation, and metabolism in field bindweed. Results of the first study indicated that aminocyclopyrachlor was just as effective when applied to the soil as it was when applied to Canada thistle foliage and was similar to aminocyclopyrachlor for up to one year after treatment. The study also revealed that Canada thistle biomass was reduced to a far greater extent when either aminocyclopyrachlor or aminopyralid was absorbed via root tissue than by emerging shoot tissue. Overall, these results suggest that Canada thistle control can be achieved even through dormant season applications, reversing the tradition of spring or fall applied herbicides to actively growing foliage and that xylem mobility throughout Canada thistle plants from root absorption may contribute to more effective weed control. Results of the second study revealed that aminocyclopyrachlor, aminopyralid, and clopyralid all had similar dissipation rates under field conditions with soil half-lives of 32.5, 28.9, and 26.6 d, respectively. Mobility of aminocyclopyrachlor and aminopyralid was limited for the first 14 d with some downward movement after 28 d, while clopyralid had more significant leaching by 14 d. Adsorption in the six soils tested was greatest with aminocyclopyrachlor, followed by aminopyralid, and clopyralid had the least soil adsorption with average Kd values across the six soils of 0.503, 0.378, and 0.236 mL g-1, respectively. Adsorption was generally correlated with soil organic matter or texture, but not with pH. These results agreed with previously published information about aminopyralid and clopyralid and shed new light on aminocyclopyrachlor soil behavior. Results of the third study showed that aminocyclopyrachlor absorption in field bindweed was maximized at 48.3% of the applied radioactivity by 48 hours after treatment (HAT). A translocation pattern of movement out of the treated leaf into the other plant tissues was revealed, with nearly equivalent aminocyclopyrachlor distribution between the treated leaf, above-ground tissue, and below-ground tissue at 192 HAT. Over the 192 h, no soluble metabolites were observed, but an increasing portion of the radioactivity was found in the fraction bound to the plant tissue. These results indicate that aminocyclopyrachlor has greater translocation to below-ground tissue in field bindweed compared with other herbicides and other weed species and aminocyclopyrachlor is not rapidly metabolized in any field bindweed plant tissue.