Herbicide sites

Patzoldt, W.L., P.J. Tranel, and A.G. Hager (2005). A waterhemp (Amaranthus tuberculatus) biotype with multiple resistance across three herbicide sites of action. Weed Sci., 53 30-36. 

Item d implies that in terms of the Hansch model of Equation 1, partitioning STEP 1 is the primary rate-controlling process characterizing the herbicidal action of the 3-TFMS compounds on Wild Mustard in the presence of Tween 80. Since all the other Hansch relationships in Table XI include fairly significant pa contributions, partitioning as well as other rate processes (possibly more intimately connected with the receptor site within the plant or seed) must be involved in determining overall herbicidal activity in these latter cases. One may speculate that the anomalous observations (a-c) above are the direct consequence of (d)—the lack of Hammett a dependence. If the pa term in the Hansch equation does indeed reflect rate or equilibrium events occurring at or near the herbicidal site of action within the plant or seed (as is often assumed but not... 

Bugg al. ( ) obtained evidence that indicated the site of photosynthetic electron transport inhibition by nitrofluorfen [2-chloro-l-(4-nitrophenoxy)-4-( trif luoromethyDbenzene], was associated with the plastoquinone-Cyt f region between PS I and PS II. This is in agreement with previous research conducted on the mechanism of action of DPE s (13, 23-27). However, in view of the above data from cucumber, these results are probably not indicative of the primary herbicidal site of action. 

This approach requires more upstream tools than the other approaches but the reward can be high-quality, information-rich leads acting at defined novel target sites. Dow AgroSciences partnered with Exelixis (South San Francisco, CA) and Exehxis Plant Sciences (Portland, OR) to implement such a multidisciplinary approach to find novel herbicide sites of action. 

According to the International Survey of Herbicide Resistant Weeds (www. weedscience.org) report, there are currentiy 434 imique cases of herbicide resistant weeds globally, involving 237 species (138 dicots and 99 monocots). Herbicide resistant weeds have been reported in 82 crops in 65 coimtries. Multiple resistances also have been observed. Weeds have evolved resistance to 22 of the 25 known herbicide sites of action and to 155 different herbicides. The evolution of herbicide-resistant weeds for selected herbicides of six leading sites of actions is shown in Table 1.4. 

Other auxin-like herbicides (2,48) include the chlorobenzoic acids, eg, dicamba and chloramben, and miscellaneous compounds such as picloram, a substituted picolinic acid, and naptalam (see Table 1). Naptalam is not halogenated and is reported to function as an antiauxin, competitively blocking lAA action (199). TIBA is an antiauxin used in receptor site and other plant growth studies at the molecular level (201). Diclofop-methyl and diclofop are also potent, rapid inhibitors of auxin-stimulated response in monocots (93,94). Diclofop is reported to act as a proton ionophore, dissipating cell membrane potential and perturbing membrane functions. 

Ben2onitrile herbicides tend to possess a high leaching potential dichlohenil is an exception, due to its stronger sorption. The hen onitrile herbicides are also prone to volatilisation losses (340) and off-site deposition (341). 

P. Bitger and G. Sandmaim, eds.. Target Sites of Herbicide Mction, CRC Press, Boca Raton, Ela., 1989. 

Herbicides. An array of herbicides are registered for use in aquatic sites, but copper sulfate and diquat dibromide are of additional interest because they also have therapeutic properties (9,10). Copper sulfate has been used to control bacteria, fungi, and certain parasites, including Jchthjophthirius (ich). Diquat dibromide can control columnaris disease, but it also exhibits fungicidal properties (9,10). EPA recentiy proposed to limit the amount of diquat dibromide, endothaH, glyphosate, and simazine that can be present in drinking water therefore, the use of these compounds may be reduced if they cannot be removed from the effluent. 

Baird is the 20-acre site of a former chemical mixing and batching company. Poor waste disposal practices resulted in the contamination of groundwater, soil, the municipal water supply, and a brook adjacent to the site. Over one hundred contaminants, including chlorinated and nonchlorinated volatile organics, heavy metals, pesticides, herbicides, and dioxins, had been identified in site soil and groundwater. Remediation activities included soil excavation and incineration, and groundwater treatment (the audit focused on the soil excavation and incineration... 

Contractors at Sites B, D, G, I, and J had incomplete sampling practices and as a result were not able to evaluate PPE levels based on monitoring data. Eor example, both contractors SSAHPs at Site I lacked provisions for monitoring site hazards such as metals, pesticides, herbicides, and semi-volatile organic compounds (SVOCs) that could not be evaluated with a PID. Since worker exposures to the range of hazards on site had not been characterized, PPE was not selected based on its performance relative to the nature and level of site hazards. 

At Site I, personnel and equipment decontamination procedures were not monitored for their effectiveness in accordance with HAZ-WOPER requirements. The Site I subcontractor did not have provisions for particulate sampling, evaluating exposure to pesticides and herbicides, or evaluating the effectiveness of site zone boundaries and personnel decontamination procedures. Additionally, monitoring had not been conducted to verify that decontamination was not necessary for employees who leave the exclusion zone and enter a clean zone without undergoing decontamination. 

Inhibitors must possess chemical and physical properties that will ensure absorption by root tips or penetration by foliar surfaces, and translocation to the active site. Once there they must assume the precise spatial configuration required to complement the molecular architecture of the active center if they are to block the key reaction. A comprehension of comparative biochemistry and information on how plants differ in the architecture of the reactive sites should assist in developing truly selective herbicides. 

Glyphosate kills plants by specifically inhibiting one critical plant enzyme used in the biosynthesis of aromatic amino acids. As such, glyphosate was one of the first commercially successful herbicides to have a primary identified enzyme site of action in plants (4,5). 

Mechanism of action can be an important factor determining selectivity. In the extreme case, one group of organisms has a site of action that is not present in another group. Thus, most of the insecticides that are neurotoxic have very little phytotoxicity indeed, some of them (e.g., the OPs dimethoate, disyston, and demeton-5 -methyl) are good systemic insecticides. Most herbicides that act upon photosynthesis (e.g., triaz-ines and substituted ureas) have very low toxicity to animals (Table 2.7). The resistance of certain strains of insects to insecticides is due to their possessing a mutant form of the site of action, which is insensitive to the pesticide. Examples include certain strains of housefly with knockdown resistance (mutant form of Na+ channel that is insensitive to DDT and pyrethroids) and strains of several species of insects that are resistant to OPs because they have mutant forms of acetylcholinesterase. These... 

The enantiomerization of phenoxyalkanoic acids containing a chiral side chain has been studied in soil using (Buser and Muller 1997). It was shown that there was an equilibrium between the R- and S- enantiomers of 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) and 2-(2,4-dichlorophenoxy)propionic acid (DCPP) with an equilibrium constant favoring the herbicidally active f -enantiomer. The exchange reactions proceeded with both retention and inversion of configuration at the chiral sites. 

This was previously used as a herbicide, and attention has been directed to its degradation in storage areas or where it has been spilled. A strain of Clostridium bifermentans KMR-1 (that is protected by a U.S. patent) was unable to use dinoseb as carbon or energy source. In the presence of a starch extract, however, a low level of transformation was observed, and the products could subsequently be mineralized by aerobic bacteria (Hammill and Crawford 1996). These observations have been extended to the remediation of soil slurries from a contaminated site by adding phosphate and starch waste that achieved anaerobic conditions, and inoculation with a culture from a pilot-scale... 

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