Herbicides groups

Phenoxyalkanoics. The phenoxyalkanoic herbicide grouping is composed of two subgroups, the phenoxyacetic acids and the phenoxypropionic acids. The phenoxyacetic acid herbicides include some of the first commercially successhil herbicides, eg, 2,4-D. They continue to be widely used for foUar control of broadleaf weeds. The more heavily functionalized phenoxypropionic acid herbicides are relatively new herbicides compared to the phenoxyacetic acids and are used primarily for selective control of grassy weeds in broadleaf crops (2,296,297). 

Triazines. Triazine herbicides are one of several herbicide groups that are heterocycHc nitrogen derivatives. Triazine herbicides include the chloro-, methylthio-, and methoxytriazines. They are used for the selective pre-emergence control and early post-emergence control of seedling grass and broadleaved weeds in cropland (299). In addition, some of the triazines, particularly atrazine, prometon [1610-18-0] and simazine [122-34-9] are used for the nonselective control of vegetation in noncropland (2). Simazine may be used for selective control of aquatic weeds (2). 

Herbicides, 11 868 13 281-345 13 524. See also Environmental fate of herbicides Growth retardants Herbicide action modes Herbicide groups... 

A number of herbicides interfere with the flow of electrons from singlet chlorophyll through the electron transport chain. The main herbicide groups and examples from these groups are shown in Table 2.1. 

Table 11.2 Occurrence of resistant weed biotypes to different herbicide groups up to 2006...

Several compounds of this herbicide group of varied structure are used for selective weed control in large quantities all over the world. 

A new active substance of the chloroacetanilide herbicide group, previously known by the code number CGA 24 705, is metolachlor, 2-chloro-6 -ethyl-N-(2-methoxy-l-methylethyl)-o-acetotoluidide (metolachlor, 18), the herbicidal properties of which have been described by Gerber el al. (1974). 

The newest member of the acetanilide herbicide group is pretilachlor, 2-chloro-2,6-diethyl-N-(2-propoxyethyl)acetanilide (22). 

The development of this selective herbicide group begun in the 1960s in the United States. Nitrofen (1) was the first member of this group, introduced by Rohm and Haas (Wilson and McRae, (1960). 

Urea herbicides form, along with phenoxy derivatives and triazines, the most important agricultural herbicide group. Since their discovery almost thirty years ago several tens of thousands of urea derivatives have been synthesised in research laboratories, and almost all of the major pesticide manufactures have marketed herbicides with a urea derivative as the active substance. 

Theoretical investigations of Domow et al. (1964) supplied the background for the discovery of this new herbicide group with asymmetric triazine skeleton. A reaction was elaborated which permitted the synthesis of l,2,4-triazin-3-ones, substituted by SR and NHj in position 3 and by NHj in position 4. 

The 3-phenoxypyridazine herbicide group was developed by Japanese workers in the mid-1960s (Tamura et al., 1956). 

Many modern herbicides act on the chloroplast, their primary target is the photosynthetic membrane (1, ). Four sites of primary herbicidal activity may be distinguished at the moment and the herbicides grouped accordingly although many compounds belong to more than one group. 

First biotypes of LoUum ri um with target-site resistance to ACCase inhibitors were identified in the early 1990s in Australia. Sdection either with an APP or a CHD herbicide resulted in target-site cross-resistance to both herbicide groups. But, regardless of whether selection was by an APP or a CHD compound, the level of resistance in these biotypes was higher to APP than to CHD herbicides. ACCase resistance factors were 30-85 for diclofop, >10-216 for haloxyfop and 1-8 for sethoxydim [31, 35, 36]. 

Amino-1,2,4-triazole has herhicidal properties. However, the substance is highly water soluble and is washed out quickly from the soil. The effectiveness can he increased hy hounding the active substance to a polymer. In this case, it is only set free slowly and acts over a prolonged period. " Polymers with pendant herbicide groups have been prepared by free radical polymerization of amino triazoles. For example, l-(4-vinylbenzo-yl)-5-amino-1,2,4-triazole, or l-(3-carbomethoxyacryloyl)-5-amino-l,2,4-... 

Polymers with pendant herbicide groups have been prepared by free radical polymerization of amino triazoles. For example, l-(4-vinylbenzoyl)-5-... 

Herbicide group Site of Action Multiple resistance... 

The research on potential inhibitors, herbicides and xenobiotics of plant lipid biosynthesis is not only a matter of general interest for agronomists and those concerned with crop protection but also for the plant biochemist, since active inhibitors represent essential tools for the characterization and better understanding of those metabolic processes and pathways which are involved in the biosynthesis of plant lipids. Theoretically all steps in plant lipid biosynthesis could be a target of inhibitors. However, only a few herbicide groups of plant lipid biosynthesis are known today. This review summarizes our present knowledge of the different types of xenobiotica and their mode of interaction with plant lipid biosynthesis. 

More studies have been conducted on the influence of the phenylurea herbicides on the soil algae in in vitro experiments that any other herbicide group, with species of Chlorella being the most frequently used. 

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