Metazachlor herbicide

The stale seedbed technique, using cultivation or a contact herbicide to kill weeds prior to drilling is frequently used. An alternative is a pre-emergence application of metazachlor herbicide. Inter-row cultivations or harrow combing are also carried out by some growers, particularly on organic farms. 

Chloroacetanilides are soil-applied herbicides used for pre- and early post-emergence control of annual grasses and broadleaf weeds in crops. Representative chloroacetanilide compounds, alachlor, acetochlor, and metolachlor, are extensively used worldwide. Other chloroacetanilides with limited usages include propachlor, bu-tachlor, metazachlor, pretilachlor, and thenylchlor. Public environmental concerns and government regulatory requirements continue to prompt the need for reliable methods to determine residues of these herbicides. There now exist a variety of analytical methods to determine residues of these compounds in crops, animal products, soil, and water. The chemical structures and major crops in which these compounds are used are summarized in Table 1. 

Hessler, D.P., V. Gorenflo, and F.H. Frimmel (1993). Degradation of aqueous atrazine and metazachlor solutions by UV and UV/H202 -Influence of pFl and herbicide concentration. Acta Hydrochim. Hydrobiol., 21 209-214. 

Chloracetanilide herbicides like alachlor, metolachlor and metazachlor can be analysed in positive-ion mode. In ESI, protonated and sodiated molecules are observed as well as the loss of methanol [16, 34, 47, 63]. The MS-MS spectmm of alachlor was stndied, nsing MS-MS and in-source CID on a orthogonal-acceleration time-of-flight mass spectrometer [63]. 

Metazachlor is a selective preemergence herbicide active on a wide range of both broad-leaved and grass weeds. It can be used selectively in Brassica spp. crops including winter oilseed rape at a rate of 1-1.8 kg active ingredient/ha. 

Butisan . [BASF AG] Metazachlor systemic herbicide controlling annual grasses, broadleaf weeds. 

Phytotoxic diloroacetamides provided a linear relationship between severe inhibition of growth and inhibition of the incorporation of [ CJoleic acid into VLCFAs in Scenedesmus acutus [7]. In higher plants, the incorporation of [ C] stearic acid or malonyl-CoA into VLCFAs was inhibited by diloroacetamides while the formation of fatty acids up to Cig was not influenced [8]. Acyl elongation with 20 0-CoA and 18 0-CoA primer substrates was inhibited by the active (S)-enantiomer of metolachlor but not by the (R)-isomer [1, 9). Inhibition of VLCFA formation was also observed in metazachlor-resistance mutant (Mz-1) cells of S. acutus [9]. Thus, the phytotoxic action of chloroacetamide herbicides is most likely by the inhibition of VLCFA synthesis. 

Xylidine can be produced by the reduction of 2,6-dimethylnitrobenzene, which is formed during nitration of m- and p-xylenes, and also by ammonolysis of 2,6-xylenol. It is used in the production of plant protection agents such as the fungicide metalaxyl Ciba Geigy) (see page 171) and the herbicide metazachlor (BASF),... 

The chloroacetamides alachlor, 2-chloro-N-(2,6-diethyl-phenyl) -N- (methoxymethyl) acetamide and metazachlor, 2-chloro-N-(2,6-dimethylphenyl)-N-(1H-pyrazol-1-ylmethyl) acetamide are selective pre-emergent or early post-emergent herbicides used to control annual grasses and many broad-leaved weeds in cotton, brassicas, maize, oilseed rape, peanuts, radish, soyabeans and sugarcane. 

In the green alga Scenedesmus acutus the uptake of 2- C) acetate, a precursor of fatty acid synthesis, is inhibited with 100 pM alachlor and 100 pM metazachlor within an incubation time of 4 h (1). There is also shown that the incorporation of the labeled acetate in acyl lipids is inhibited. After 16 h and 40 h incubation with a herbicide concentration of 5 yM the fatty acid content of the green alga changed, as shown in the table. 

In the presence of metazachlor, alachlor or dimethenamid (5 pM) fatty acid desaturation in S, acutus was strongly inhibited after 40 h. Under these conditions the relative amounts of polyunsaturated fatty acids decreased while palmitic and oleic acids accumulated (Table 1). In an in-vitro assay, desaturation of oleoyl-CoA by microsomes was also decreased by chloroacetamides, suggesting a direct influence of the herbicides on oleic acid desaturation, although 25 pM were necessary for a significant inhibition (Table 2). l C-oleic acid fed to the algae was rapidly incorporated into the lipids and further desaturated. It was also incorporated into a precipitate obtained after saponification of the cells or lipid extraction. Radioactivity in that fraction was dramatically reduced by metazachlor, a concentration between 10 nM and 100 nM was sufficient for a 50% inhibition [3]. This effect was correlated with... 

Chloroacetamides induce an accumulation of 18 1 in 5. acutus and inhibit 18 1 desaturation in vitro. Furthermore, they dramatically reduce the incorporation of 18 1 into a non-extractable fraction after lipid or fatty acid extraction. This inhibition is specific to 18 1, requires metabolically active cells, and does not occur in a metazachlor tolerant line [6]. Oleic acid metabolism could thus play a central role in the mode of action of chloroacetamides. The NEF is currently under further investigation and its analysis might lead to the primary target of the herbicides. 

Presently the tolerant cells grow in the presence of 4.8 pM metazachlor as fast as the wild line. Microscopically the tolerant cells look like cells treated with herbicide, they are round and single while those of the wild line are lens-shaped and in colonies (coenobia) of 8 cells. This cell line is also resistant against other herbicides from related classes Dimethenamid (a thiophenamide) and mefenacet (an oxy acetamide). 

Incorporation of C-oleic acid into a non-extractable fraction obtained after saponification of the cells is highly sensitive to metazachlor (I50 < 10" M) [5]. This effect could not be demonstrated in the tolerant cells even with 1000 fold higher herbicide concentrations (Figure 2), confirming a causal relation between incorporation of oleic acid into that fraction and herbicidal activity. In the tolerant line less label was recovered in the fatty acid fraction, indicating a lower uptake of oleic acid into the tolerant cells. HPLC analysis of the radioactive fatty acids showed that although... 

Couderchet M, Brozio B, Boger P. Effect and metabolism of the chloroacetamide herbicide metazachlor comparison of plant cell suspension cultures and seedlings. J Pestic Sci 1994 19 127-135. 

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