Cereals sulfonylurea

Table 2.2.6 Cereal sulfonylurea herbicides in order of market introduction.

The first ALS-resistant weeds were reported in 1987 when prickly lettuce (Mallory-Smith, 1990 Mallory-Smith et al, 1990b) and kochia (Primiani et al, 1990) control failures occurred in Idaho and Kansas, respectively, after 5 consecutive years of chlorsulfuron use. The kochia biotype proved to be cross-resistant to six other ALS-inhibitor herbicides, including sulfonylureas and imidazolinones. Within 5 years, sulfonylurea-resistant kochia had been identified at 832 sites in 11 states of the United States and in three Canadian provinces (Saari et al, 1994). ALS inhibitor-resistant kochia and Russian thistle have become widespread problems in cereal-producing regions of northwestern United States and Canada. The mobility of these tumble weeds as plants with mature seeds or pollen carried by wind has undoubtedly contributed to the rate at which resistance has spread. 

Brown, H.M. (1990). Mode of action, crop selectivity and soil relations of the sulfonylurea herbicides. Pesticide Sci., 29 263-281. Brown, H.M., F.T. Lichtner, J.M. Hutchison, and J.A. Saladine (1995). The impact of sulfonylurea herbicides in cereal crops. Brighton Crop Prot. Conf.-Weeds,3 1143-1152. 

ALS herbicides. Two classes of ALS-inhibiting herbicides are the sulfonylurea herbicides, discussed in Sections 2.1.2.1 and 2.2.3.1, and the imidazolinone herbicides. A third class of ALS-inhibiting herbicides is the 1,2,4-triazolo [1,5-a]pyrimidine-2-sulfonanilides. The triazolopyrimidine sulfonanilides act by disrupting the biosynthesis of branched chain amino acids in plants. Representatives of this class of herbicides include florasulam (Boxer , Nikos ) [151], initially introduced in Belgium in 1999 and used for the postemergence control of broadleaf weeds in cereals and corn, and flumetsulam (Broadstrike ) [152], used alone or in combination with other herbicides for the control of broadleaf weeds in soybean and corn. 

Flucetosulfuron [188,189] is a sulfonylurea experimental postemergence herbicide for controlling grasses such as barnyard grass in rice and broadleaf weeds such as Galium aparine in cereals. It shares with previously introduced sulfonylurea herbicides a common mode of action, inhibition of the ALS enzyme, a key enzyme in the biosynthesis of branched amino acids, such as leucine, isoleucine, and valine [76],... 

Sulfonylureas, e.g. chlorsulfuron (69), are an important group of herbicides which will selectively control many broad-leaved weeds in cereals at remarkably low doses ( 20g/ha 1 lha = 104m2). Chlorsulfuron (69), can be synthesised from chlorobenzene by treatment with chlorosulfonic acid, which yields a mixture of the o-and -sulfonyl chlorides. The desired o-sulfonyl chloride (79) is separated... 

The selective toxicity of sulfonylureas to certain weeds without damage to the cereal crop arises from their rapid metabolism in the crop plant to inactive compounds, whereas in sensitive weeds the metabolism is much slower. The very high herbicidal activity suggests a specific biochemical mode of action, which is concluded to be the inhibition of plant cell division. Sulfonylureas block the enzyme acetolacetate synthase (ALS), which catalyses the biosynthesis of the essential branched chain amino acids valine, leucine and isoleucine. 

General LC/MS Conditions for Sulfonylurea Multiresidue Analysis. We have developed general thermospray LC/MS conditions for the purpose of separating and detecting six different sulfonylurea herbicides. These conditions can be used as a guide fra- a variety of LC/MS residue applications which may require the analysis of one or more of these herbicides. Our procedure includes GLEAN (chlorsulfuron), ALLY (metsulfuron methyl), HARMONY (thiameturon) and EXPRESS cereal herbicides, CLASSIC (chlorimuron ethyl) soybean herbicide and OUST (sulfometuron-methyl) noncrop land herbicide. (Structure 1)... 

The systemic morpholine fungicide Corbel with fenpropimorph as its active substance is frequently applied to cereal cropping. It is rapidly metabolized in soil to fenpropimorphic acid. For the assay of fenpropimorphic acid in soil, GC-MS coupling109 has been proposed. The GC technique was used to assure the best separation for the fenpropimorphic acid from the complex soil matrix. The MS technique is very sensitive and assures the best reliability of the analytical information. The same reliability is also achieved when the HPLC-MS tandem system is used for sulfonylurea herbicide assay in soil.110... 

Herbicides derived from urea form a large group of chemical compounds widely used in agriculture to control weeds in cereal, vegetable, and fruit tree crops. On the basis of their chemical natures, use, and mode of action, substituted urea herbicides can be divided into two main groups — phenylureas and sulfonylureas. 

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. 

Iodosulfuron-methyl-sodium was the first safened sulfonylurea herbicide on the market [17, 18] when introduced in 1999 and has been commercialized by Bayer CropScience for use both in cereals and maize. A safener such as mefen-pyr-diethyl (cf Fig. 2.2.2) is a chemical that, when applied to crop plants, reduces the injury caused by herbicides to an acceptable level. A safener ideally does not... 

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... 

A new sulfonylurea herbicide for use in cereals, rice and sugarcane, Proc. 

D. S. M. D Souza, I. A. Black, R. T. Hewson, Amidosulfuron — a new sulfonylurea for the control of Galium aparine and other broadleaf weeds in cereals, BCPC Conference — Weeds 567-72 (1993). 

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. 

The ultimate success of this discovery is demonstrated by the fact that there are fourteen commercialized and advanced candidate sulfonylurea herbicides. These compounds are useful in crops such as cereals, soybeans, rice, com, and canola as well as for noncrop use. TTieir low use rates favorable soil half-lives and low mammalian toxicity make them ideal products environmentally. These factors arc discussed in more detail by Brown and Kearney in the following chapter. 

Attempted chlorosulfonation of 3- and 4-chlorophenylureas failed, presumably as a result of a combination of unfavourable stereoelectronic factors. Sulfonylureas are an important group of highly potent herbicides which may be used for selective weed control in cereals at very low dose rates. Herbicidal (p-sulfamoyl)phenylureas were synthesized from the appropriate phenylureas by mixing them with chlorosulfonic acid at 12-15 C, followed by heating at 60 C and the resultant p-(chlorosulfonylphenyl)ureas were condensed with the amine. °... 

In 1982, DuPont introduced the sulfonylurea herbicides which are effective at remarkably low dose rates an important example is chlorsulfuron 22 used for selective control of broad-leaved weeds in cereals at rates of 10-40 gha this herbicide can be prepared from chlorobenzene 21 (Scheme 5) (see also Chapter 6, ref 33), The first stage of the synthesis, namely the reaction of chlorobenzene with chlorosulfonic acid yields a mixture of the o- and / -sulfonyl chlorides, which may be separated by fractional distillation, since the o-isomer has the lower bp (Chapter 6, ref 33). 

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