Prairie wetlands are affected by agricultural activities, in particular herbicide contamination of wetland ecosystems. The environmental fate of herbicides in wetlands is determined by their persistence and transport. Currently, little is known about the persistence of commonly used herbicides in wetland water and sediment. The objective of this dissertation was to determine the importance of wetland sediments in influencing the fate of commonly used herbicides in prairie wetlands.<p> Sediment sorption is an important dissipation pathway for herbicides. The effects of land use on physicochemical properties of wetland sediment, and the associations between these properties and herbicide sorption characteristics for four herbicides (trifluralin, atrazine, 2,4-D and glyphosate), were examined for 17 wetlands.<p> The sorption of herbicides in sediment increased in the order of 2,4-D < atrazine < glyphosate < trifluralin. Overall, sediments from wetlands that were recently cultivated had lower total organic carbon (TOC), total inorganic carbon (TIC), electrical conductivity (EC), exchangeable cation (EXCAT), cation excheageable capacity (CEC), and sorption coefficient (Kd) values (2,4-D, trifluralin, and atrazine) than sediments from semi-permanent and riparian ephemeral wetlands. Although TOC content was correlated to the sorption of 2,4-D, trifluralin and atrazine, riparian wetland sediments despite having a lower TOC content than semi-permanent wetland sediments, had the highest herbicide sorption capacity for 2,4-D, trifluralin and atrazine.<p> To further examine the link between land use and herbicide sorption by sediment, a multi-residue analytical method was developed to quantify seven sulfonylurea herbicides commonly used in crop production (thifensulfuron-methyl, tribenuron-methyl, ethametsulfuron-methyl, metsulfuron-methyl, rimsulfuron, nicosulfuron and sulfosulfuron) in sediment from 17 wetlands. Sediment was extracted with deionized water using pressurized liquid extraction and the resultant extracts were cleaned-up using Oasis HLB solid-phase extraction cartridges. Quantification and confirmation were performed using liquid chromatography interfaced with positive ion electrospray tandem mass spectrometry, and multiple reaction monitoring. Calibration curves were linear with correlation coefficients greater than 0.994 and limits of quantification ranged from 1.0 to 2.0 µg kg-1. Ethametsulfuron-methyl, sulfosulfuron and metsulfuron-methyl, the three most environmentally persistent of the seven sulfonylurea herbicides monitored in this study, were most frequently detected in wetland sediment. The concentrations of sulfonylurea herbicides were higher in sediments from the semi-permanent wetland, which received surface runoff from a larger catchment. <p> To assess the relationship between herbicide dissipation and sorption to sediment, seven commonly used herbicides (glyphosate, dicamba, bromoxynil, 2,4-D, MCPA, mecoprop-P and dichlorprop) were applied to one half of an ephemeral (E) and a semi-permanent (SP) prairie wetland to mimic a direct overspray event, a worst-case scenario for wetland contamination. Water and sediment samples collected over a 77-d study period (early June to late August) were analyzed for herbicide concentration; aminomethylphosphonic acid (AMPA), the degradation product of glyphosate, was also monitored. Glyphosate dissipated rapidly in the water column of each wetland with DT50 values of 3.7 d for wetland E and 6.9 d for wetland SP. The mass of AMPA in each wetland increased with a concomitant decrease in the mass of glyphosate, suggesting that glyphosate degradation was occurring in the water column. In addition, glyphosate was also lost from the water column via sorption to bottom sediment, as evidenced by its detection in sediment samples up to 42-d post-treatment (39.0 224.5 µg kg-1). The DT50 of the other six acid herbicides ranged from 2.3 d (bromoxynil) to 31 d (dichlorprop). The two chiral herbicides, mecoprop-P and dichlorprop, were the most persistent acid herbicides in the water column. Sorption to sediment was also an important dissipation route for these six herbicides in water, especially in wetland E. After 77 d in the semi-permanent wetland and 56 d in the ephemeral wetland, the concentrations of bromoxynil, dicamba and 2,4-D were below the Canadian Water Quality Guidelines for the Protection of Aquatic Life. Concentrations of the more persistent herbicides (mecoprop-P and dichlorprop) remained at levels above the guidelines.<p> Use of bromide ion as a conservative tracer indicated that some of the water loss from both wetlands was via infiltration. Because there was a strong correlation between the decrease in bromide ion and herbicide mass in the water column, it is possible some herbicides were lost from the water column along with the infiltrating water. Infiltration to wetland margins during this part of the growing season would have been largely driven by the riparian vegetation surrounding both wetlands.<p> Overall, this thesis demonstrated the importance of sediment in the dissipation of currently used herbicides in wetland ecosystems. Both laboratory sorption studies and whole-wetland experiments provided insights on the sorptivity of herbicides in sediment as well as their persistence in water and sediment.

Prairie wetlands are affected by agricultural activities, in particular herbicide contamination of wetland ecosystems. The environmental fate of herbicides in wetlands is determined by their persistence and transport. Currently, little is known about the persistence of commonly used herbicides in wetland water and sediment. The objective of this dissertation was to determine the importance of wetland sediments in influencing the fate of commonly used herbicides in prairie wetlands.<p> Sediment sorption is an important dissipation pathway for herbicides. The effects of land use on physicochemical properties of wetland sediment, and the associations between these properties and herbicide sorption characteristics for four herbicides (trifluralin, atrazine, 2,4-D and glyphosate), were examined for 17 wetlands.<p> The sorption of herbicides in sediment increased in the order of 2,4-D < atrazine < glyphosate < trifluralin. Overall, sediments from wetlands that were recently cultivated had lower total organic carbon (TOC), total inorganic carbon (TIC), electrical conductivity (EC), exchangeable cation (EXCAT), cation excheageable capacity (CEC), and sorption coefficient (Kd) values (2,4-D, trifluralin, and atrazine) than sediments from semi-permanent and riparian ephemeral wetlands. Although TOC content was correlated to the sorption of 2,4-D, trifluralin and atrazine, riparian wetland sediments despite having a lower TOC content than semi-permanent wetland sediments, had the highest herbicide sorption capacity for 2,4-D, trifluralin and atrazine.<p> To further examine the link between land use and herbicide sorption by sediment, a multi-residue analytical method was developed to quantify seven sulfonylurea herbicides commonly used in crop production (thifensulfuron-methyl, tribenuron-methyl, ethametsulfuron-methyl, metsulfuron-methyl, rimsulfuron, nicosulfuron and sulfosulfuron) in sediment from 17 wetlands. Sediment was extracted with deionized water using pressurized liquid extraction and the resultant extracts were cleaned-up using Oasis HLB solid-phase extraction cartridges. Quantification and confirmation were performed using liquid chromatography interfaced with positive ion electrospray tandem mass spectrometry, and multiple reaction monitoring. Calibration curves were linear with correlation coefficients greater than 0.994 and limits of quantification ranged from 1.0 to 2.0 µg kg-1. Ethametsulfuron-methyl, sulfosulfuron and metsulfuron-methyl, the three most environmentally persistent of the seven sulfonylurea herbicides monitored in this study, were most frequently detected in wetland sediment. The concentrations of sulfonylurea herbicides were higher in sediments from the semi-permanent wetland, which received surface runoff from a larger catchment. <p> To assess the relationship between herbicide dissipation and sorption to sediment, seven commonly used herbicides (glyphosate, dicamba, bromoxynil, 2,4-D, MCPA, mecoprop-P and dichlorprop) were applied to one half of an ephemeral (E) and a semi-permanent (SP) prairie wetland to mimic a direct overspray event, a worst-case scenario for wetland contamination. Water and sediment samples collected over a 77-d study period (early June to late August) were analyzed for herbicide concentration; aminomethylphosphonic acid (AMPA), the degradation product of glyphosate, was also monitored. Glyphosate dissipated rapidly in the water column of each wetland with DT50 values of 3.7 d for wetland E and 6.9 d for wetland SP. The mass of AMPA in each wetland increased with a concomitant decrease in the mass of glyphosate, suggesting that glyphosate degradation was occurring in the water column. In addition, glyphosate was also lost from the water column via sorption to bottom sediment, as evidenced by its detection in sediment samples up to 42-d post-treatment (39.0 224.5 µg kg-1). The DT50 of the other six acid herbicides ranged from 2.3 d (bromoxynil) to 31 d (dichlorprop). The two chiral herbicides, mecoprop-P and dichlorprop, were the most persistent acid herbicides in the water column. Sorption to sediment was also an important dissipation route for these six herbicides in water, especially in wetland E. After 77 d in the semi-permanent wetland and 56 d in the ephemeral wetland, the concentrations of bromoxynil, dicamba and 2,4-D were below the Canadian Water Quality Guidelines for the Protection of Aquatic Life. Concentrations of the more persistent herbicides (mecoprop-P and dichlorprop) remained at levels above the guidelines.<p> Use of bromide ion as a conservative tracer indicated that some of the water loss from both wetlands was via infiltration. Because there was a strong correlation between the decrease in bromide ion and herbicide mass in the water column, it is possible some herbicides were lost from the water column along with the infiltrating water. Infiltration to wetland margins during this part of the growing season would have been largely driven by the riparian vegetation surrounding both wetlands.<p> Overall, this thesis demonstrated the importance of sediment in the dissipation of currently used herbicides in wetland ecosystems. Both laboratory sorption studies and whole-wetland experiments provided insights on the sorptivity of herbicides in sediment as well as their persistence in water and sediment.

Triflxysulfuron is a sulfonylurea herbicide developed for postemergence weed control in cotton, sugarcane, and turf. Greenhouse and laboratory studies were conducted at the Texas A&M University campus and at the USDA-ARS research facility in Stoneville, MS to: 1) quantify the dissipation of trifloxysulfuron in a spray tank at 0, 1, 3, 7, 14, and 21 d after mixing as influenced by pH of the spray carrier and evaluate the resulting effects on efficacy on Palmer amaranth (Amaranthus palmeri S. Wats); 2) determine the effect of spray carrier pH on absorption and translocation of radiolabeled trifloxysulfuron in Palmer amaranth and Texasweed (Caperonia palustris (L.) St. Hil.); 3) determine average edge-of-field concentrations, total mass losses, and fractional losses of trifloxysulfuron applied to cotton at the 5-leaf stage and to bare soil as influenced by simulated rainfall. The dissipation of trifloxysulfuron followed first-order kinetics. Calculated half-life values indicated that hydrolysis occurred more rapidly with the more acidic spray carriers with little or no difference between neutral and alkaline pH levels. Bioassay on Palmer amaranth showed no differences in plant dry weights due to pH level or dissipation time. The absorption of 14C-trifloxysulfuron was greater for Palmer amaranth than for Texasweed when averaged over time and pH. Altering pH did not affect the translocation of trifloxysulfuron in Palmer amaranth. In contrast, translocation of 14C-trifloxysulfuron in Texasweed increased in the order of pH 5 < pH 7 = pH 9. Cumulative trifloxysulfuron losses in runoff from cotton plots were 0.21 g ha-1 while losses from bare plots were 0.13 g ha-1. These values corresponded to fractional losses of 2.7% for cotton plots and 1.7% for bare plots of the total amount applied. These studies provide important information regarding the stability, plant uptake, and runoff potential of a commonly used sulfonylurea herbicide.

Thesis (MScAgric)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Birdsfoot Trefoil (Lotus corniculatus L. cv. Leo), is a perennial forage legume that has difficulty in establishing stands due to slow seedling growth, weed competition and herbicide sensitivity. The development of herbicide resistant cultivars would be of economic importance. Resistant lines were isolated after sequential selection at the callus, shoot and whole plant levels to the sulfonylurea (SU) herbicides Harmony (DPX-M6316, code name for methyl 3- ( ( ((4-methoxy-6-methyl-1,3,5,triazine-2-yl)amino) carbonyl) amino) sulfonyl-2-thiophenecarboxylate), or Classic (DPX-F6025, code name for 2(( (4-chloro-6-methoxypyrimidine-yl)amino carbonyl) aminosulfonyl)benzoic acid ethyl ester. In field and growth chamber tests the Harmony regenerant lines displayed an increased tolerance as compared to control plants from tissue culture, and from seed. Results of the evaluation of callus cultures of regenerated mutant lines signify stability of the resistance. Outcrossed seeds collected from field trials, and tested in vitro for herbicide resistance, indicate that the trait is heritable and that resistance may be due to reduced sensitivity of acetolactate synthase to SU inhibition. It is concluded that herbicide resistant birdsfoot trefoil cultivars can be isolated using in vitro selection.

No description available.

Field experiments were conducted at Carman, Manitoba to determine the effect of tank-mixing different contact herbicides with glyphosate and time of application of harvest aid herbicides on residue accumulation in dry bean seed and the effect of tank-mixing a contact herbicide with glyphosate on weed control. Carfentrazone-ethyl in mixture with glyphosate was the least effective harvest aid herbicide and did not fully desiccate plant parts or reduce glyphosate residues in the seed to less than 2 ppm. Saflufenacil, diquat, flumioxazin, and glufosinate in mixture with glyphosate effectively desiccated all plant and reduced glyphosate residue accumulation in the seed. Saflufenacil in mixture with glyphosate provided the most consistent efficacy on three weed species. Time of application of harvest aid herbicides influenced residue accumulation and yield; however, all harvest aids applied at or after 75% pod colour change had no negative effect on yield and significantly reduced the risk of residue accumulation.

The glutathione transferases (GSTs) of maize have been the most studied GSTs in plants, however much is still not known about these enzymes. In the course of the current study six GST subunits (Zm GSTs I, II and III, which have been reported previously, and Zm GSTs V, VI and VII, which have not been previously reported) have been identified in the dimers Zm GST I-I, I-II, I-III, V-V, V-VI and V-VII. Maize GSTs are known to be important in herbicide detoxification and the purified maize enzymes were each found to have differing activities toward a number of herbicides, and also a range of other potential GST substrates. Additionally, Zm GST I II and Zm GST V-V possessed glutathione peroxidase activity. The developmental regulation and chemical inducibility of maize GSTs were studied in maize seedlings using western blotting, with different subunits showing markedly different responses. Zm GST I was constitutively present in all plant parts and unaffected by chemical treatment, Zm GST II was only detected in young roots but was induced in roots and shoots by many different chemical treatments, and Zm GST V was present at low levels throughout maize plants, with levels enhanced greatly by treatment with the safener dichlormid but not by other chemicals tested. cDNA clones corresponding to Zm GST subunits I, III, V, VI and VII were isolated by library screening using antibody or DNA probes. The cDNA sequences for Zm GST subunits V, VI and VH were different from those of previously cloned type I (theta class) maize GSTs and were most similar to the auxin-regulated GST family (type III or tau class GSTs) previously only identified in dicotyledonous species. The cloned GSTs were expressed as recombinant proteins in E. coli, allowing further characterisation, including detailed kinetic analysis for recombinant Zm GST I-I and Zm GST V-V.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Applied and Molecular Ecology, 2000? / Bibliography: leaves 151-172.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 137-139). Also available via the Internet.