Mesosulfuron-methyl

The objective of this Chapter is to give an overview of the sulfonylurea herbicides that either have been introduced to the market since 1995 or are currently in their later stages of development. These include flupyrsulfuron-methyl-sodium, sulfosulfuron, iodosulfuron-methyl-sodium, mesosulfuron-methyl, trito-sulfuron and monosulfuron for use in cereals ethoxysulfuron, azimsulfuron, cyclosulfamuron, flucetosulfuron, TH 547 and orthosulfamuron in rice foram-sulfuron in maize oxasulfuron in soybeans and trifloxysulfuron-sodium in sugarcane and cotton. 

Mesosulfuron-methyl (AE F130060) (Table 2.2.11) [19] was the second safened sulfonylurea herbicide for cereal crops to be commercialized. This compound was introduced in 2001 and has been commercialized by Bayer CropScience [20, 21]. Its strength is broad-spectrum post-emergence grass weed control. Mesosulfuron-methyl, at a dose rate of 4.5-15 g-a.i. ha , reliably controls 24 different grass weed species from 12 different families. Among the commercially... 

Mesosulfuron-based products Formu- lation type Mesosulfuron- methyl lodosulfuron- methyl sodium Diflu- fenican Propoxy- carbazone Mefenpyr- diethyl... 

Apera and Alopecurus, are also successfully controlled by uptake of mesosulfuron-methyl via the soil and the roots. 

Scheme 2.2.3. Metabolic pathway of mesosulfuron-methyl in soil under aerobic and anaerobic conditions (compounds labeled in bold were detected at >10% of the applied radioactivity).

The main soil degradation pathways of sulfonylurea herbicides are cleavage of the sulfonylurea bridge, O- and N-dealkylation reactions, aryl and aliphatic hydroxylation reactions, dehalogenation and ester hydrolysis. It is not within the scope of this chapter to discuss each of these in detail for all of the above-mentioned new sulfonylureas. Instead mesosulfuron-methyl is taken below as a general illustration of commonly found soil degradation pathways established within the sulfonylurea family. 

G. Borrod, R. Bmsche, Mesosulfuron-methyl - a new active ingredient for grass weed control in cereals, Proc. BCPC Conference - Weeds 43—48 (2001). 

Fig. 5.1. Post-emergence safening of wheat by mefenpyr-diethyl against mesosulfuron-methyl. (A) Untreated (B) mesosulfuron-methyl at 60 g-a.i. ha h and (C) mesosulfuron at 60 g-a.i. ha" plus mefenpyr-diethyl at 30 g-a.i. ha" .

As already pointed out, mefenpyr-diethyl is a versatile safener and it has been commercialized in combinations with several single or mixed herbicides, including fenoxaprop-P-ethyl (e.g.. Puma S ), iodosulfuron-methyl-sodium (e.g.. Hussar ) and mesosulfuron-methyl (Atlantis ). In general, the quantity of mefenpyr-diethyl required to provide adequate safening lies between 20 and 100 g-a.i. ha , and there is no set ratio between the rates of the herbicides and... 

Uptake studies were also carried out with the recently developed combinations of the safener mefenpyr-diethyl with the sulfonylurea herbicides mesosulfuron-methyl and iodosulfuron-methyl-sodium, which are used for selective postemergence weed control in wheat crop. In both combinations the safener had no influence on herbicide uptake [29]. 

As already mentioned, it is a major advantage of mefenpyr-diethyl to act as a safener also in combination with sulfonylurea herbicides in cereal species. Combinations have been developed with the sulfonylureas iodosulfuron-methyl-sodium and mesosulfuron-methyl. 

Fig. 5.2. Examples of herbicide detoxification reactions stimulated by the safener mefenpyr-diethyl. (A) Conjugation reaction of fenoxaprop with glutathione (GSH). (B) Oxidative demethylation of mesosulfuron-methyl.

XXXIII Mesosulfuron methyl H Inhibits biosynthesis of branched AA like I >5000... 

Newer selectively acting herbicides are the compounds amidosulfuron (I), mesosulfuron methyl (XXXIII) and nicosulfuron (XXXVI), which belong to the class of sulfonyl ureas. Since they are very active, the amount used is very small (compare atrazine (III) and nicosulfuron (XXXVI) in Table 9.6). As in the case of the other PPA, the biochemical mechanism of action of most of the herbicides is known (examples in Table 9.5). They frequently target a reaction site in the chloroplasts. 

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