Herbicide modes

Transgenic soybean plants expressing the CTP-CP4 EPSPS display commercial levels of Roundup tolerance. These results vaUdate the importance of substrate kinetics of EPSPS in order to maintain adequate rates of aromatic biosynthesis. Furthermore, the fact that glyphosate tolerance can be obtained by expression of a glyphosate-tolerant EPSPS illustrates that the herbicidal mode of action of glyphosate is related solely to inhibition of the EPSPS reaction. 

Biorational approaches have proven useful in the development of classes of herbicides which inhibit essential metaboHc pathways common to all plants and thus are specific to plants and have low toxicity to mammalian species. Biorational herbicide development remains a high risk endeavor since promising high activities observed in the laboratory may be nullified by factors such as limitations in plant uptake and translocation, and the instabiHty or inactivity of biochemical en2yme inhibitors under the harsher environmental conditions in the field. Despite these recogni2ed drawbacks, biorational design of herbicides has shown sufficient potential to make the study of herbicide modes of action an important and growing research area. 

This herbicidal mode of action of pyraflufen-ethyl is similar to those of other peroxidizing herbicides containing a diphenyl ether moiety. Herbicidal effects of pyraflufen-ethyl are revealed as yellowing and browning in the foliar portion, and then death of the whole plant with leaf burn. 

Grossmann K, Kwiatkowski J, Evidence for a causative role of cyanide, derived from ethylene biosynthesis, in the herbicidal mode of action of quinclorac in barnyard grass, Pestic Biochem Physiol 51 150-160, 1995. 

Table 2.2 Summarised table of herbicide modes of action...

Ross, M.A. and Childs, D.J. Herbicide Mode-of-Action Summary. Purdue Cooperative Extension Service, WS-23-W, April 1996 revision (1996) http // www.ces.purdue.edu/extmedia/WS/ WS-23-W.html (last accessed 30 April... 

Research had confirmed that no parent simazine residues were found in treated com plants, and additional data on the dissipation pathway of simazine needed to be developed. Research also indicated that triazines interfered with the photosynthetic process on susceptible growing weeds, as evidenced by the appearance of chlorotic leaves. Steps were undertaken to elucidate simazine s dissipation pathway and herbicidal mode of action. In Basel, Dr. Gast (1958) showed that the accumulation of starch by common coleus (Coleus blumei Benth.) plants was inhibited from treatment with 2-chloro-4,6-bis-(alkyl-amino)-triazines due to the inhibition of sugar synthesis. At the same time, Moreland et al. (1958) found weed control activity could be reduced by supplying carbohydrates to the plants through their leaves and that simazine was a strong inhibitor of the Hill reaction in photosynthesis. Exer (1958) found that triazines inhibited the Hill reaction as strongly as urea of the CMU (monuron) type. 

Botanists, physiologists, and chemists were able to develop sensitive methods for residue analysis (Delley et al., 1967). They also developed a clear understanding of the herbicidal mode of action and the metabolic pathway of. v-triazines in plants, soil, and animals (Kniisli et al., 1969). These early investigations were supported by cooperation from universities in the United States and Europe where scientists recognized that these compounds would be very important tools for worldwide agriculture and to manage weeds in noncropland. 

Until the mid-1990s, multiple-resistance (i.e., resistance to more than one herbicide mode of action within the same biotype) had not been reported within North America. However, Foes et al. (1996) found a kochia biotype from western Illinois resistant to atrazine and several ALS-inhibiting herbicides. Lopez-Martinez et al. (1996) reported that a triazine-resistant Echinochloa species found in atrazine-treated com also showed cross-resistance to quinclorac. Clay and Underwood (1989) and Clay (1989) reported that one triazine-resistant biotype of American willowherb was also resistant to paraquat from a hop garden in the United Kingdom treated annually for 25 years with simazine and paraquat. 

Based on our knowledge of herbicide modes of action and other characteristics, we are able to predict, with some confidence, which herbicides will have a high risk for resistance. There are wide margins for error due to uncertainty about genetic variability of weeds (i.e., the relative frequency of occurrence of different resistance mutations), the lack of knowledge on the primary sites or modes of action for certain herbicides, and the lack of understanding of cross-resistance between classes of herbicides. 

Peterson DE et al., Herbicide Mode of Action, C-715, Kansas State University Agricultural Experiment Station and Cooperative Extension Service, Kansas State University, Manhattan, KS, January, 2001. 

The herbicidal mode of action of pyrazon is not yet completely known. In addition to inhibiting photosynthesis, pyrazon reduces COj-assimilation, Oj-uptake and the catalase activity in the leaves. All of these phenomena are manifested more strongly in the sensitive plants than in tolerant beet. 

Chemical Genetics, Target Site Identification, Resistant Mutants, Herbicide Mode of Action, Auxins, Arahidopsis... 

CropLife Australia, in Managing resistance, Herbicide Mode of Action Groups, http //www.croplifeaustralia. org.au, update 2005, 1-3. 

As discussed in detail in Chapter 4.2, triketones exert their herbicidal mode of action by inhibition of 4-hydroxyphenylpyruvate dioxygenase (HPPD) [6]. Triketones are not the only herbicide class that have this mode of action, and it has retrospectively been shown that apparently structurally non-related heterocyclic commercial herbicides such as isoxaflutole (7, BALANCE and MERLIN ), and the rice herbicides pyrazolate (8, SANBIRD ) and benzobicyclon (9, SHOW-ACE ) also cause these bleaching symptoms by the same mode of action. However, a common feature of these herbicides, after metabolic activation to the active metabolites (7 ) [7], (8 ) [8] and (9 ) [9] is the presence of an acidic 1,3-dicarbonyl moiety, which is also present in triketones (Fig. 4.3.2). Triketones and related her-... 

To be successful in the future a company has to develop novel solutions for weed control with superior agronomic properties properties that would alter the market-landscape or which even would create new market segments. Compounds with novel herbicidal Modes of Action (MoA) would have the potential to fulfill these requirements. They would have the potential to open new segments and to trigger above average growth of the herbicide market. 

The herbicidal mode of action of benzoxazinoids is unknown. Sanchez-Moreiras et al. [127] reviewed what was known of the mode of action of BOA up until about 2003. BOA can inhibit mitochondrial function by interfering with both electron transport and mitochondrial ATPase activity [128]. A correlation between inhibition of plasma membrane H " -ATPase activity and inhibition of growth by BOA and DIBOA [129], suggests that their effects on nutrient uptake and electrolyte leakage could be caused by this primary effect [130]. BOA reduces the number of dividing meristematic... 

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