Chlorsulfuron is an ALS (acetolactate synthase) inhibitor herbicide, and is a

sulfonylurea Sulfonylureas (UK: sulphonylurea) are a class of organic compounds used in medicine and agriculture, for example as antidiabetic drugs widely used in the management of diabetes mellitus type 2. They act by increasing insulin release from the bet ...

compound. It was discovered by

George Levitt George may refer to: People * George (given name) * George (surname) * George (singer), American-Canadian singer George Nozuka, known by the mononym George * George Washington, First President of the United States * George W. Bush, 43rd President ...

in February 1976 while working at DuPont, which was the patent assignee.

Brand names

Originally introduced in 1982 under the brand name Glean by DuPont, later also as Telar, in North America.

Chemistry

The first synthesis of chlorsulfuron was disclosed in a patent filed by DuPont in 1977. 2-Chlorobenzenesulfonyl isocyanate was condensed with 2-amino-4-methoxy-6-methyl-1,3,5-triazine to form the

product. : Chlorsulfuron synthesis

Mode of action

Chlorsulfuron is an herbicide of the acetolactate synthase inhibitor (ALS inhibitor) class, HRAC (Herbicide Resistance Action Committee) group 2 (legacy HRAC Group B).

Efficacy

Triticum aestivum Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield. Ta ...

'' is naturally resistant via aryl hydroxylation then

conjugation Conjugation or conjugate may refer to: Linguistics * Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics * Complex conjugation, the chang ...

with glucose compounds into non-herbicidal conjugates. Widespread weed resistance to chlorsulfuron has been found across North America and around the world. ''T. aestivum''s close relative ''

Lolium rigidum ''Lolium rigidum'' is a species of annual grass. Common names by which it is known include annual ryegrass, a name also given to Italian ryegrass (''Lolium multiflorum''), rigid ryegrass, stiff darnel, Swiss ryegrass and Wimmera ryegrass. It is ...

'' was found to be using the same mechanism by Christopher et al 1991 and Cotterman & Saari 1992. A North American population of '' Stellaria media'' was found by Hall and Devine 1990 to be resistant by way of an ALS target mutation rather than by improved disposal. Increased

P450 Cytochromes P450 (CYPs) are a superfamily of enzymes containing heme as a cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various compo ...

activity can also be effective, such as in '' Alopecurus myosuroides'' (found by Letouzé and Gasquez 2003), and ''L. rigidum'' (by Tardif and Powles 1999). Another such mechanism - the

acetolactate synthase The acetolactate synthase (ALS) enzyme (also known as acetohydroxy acid or acetohydroxyacid synthase, abbr. AHAS) is a protein found in plants and micro-organisms. ALS catalyzes the first step in the synthesis of the branched-chain amino acids ( ...

target-site mutation Pro-197–Ser - was found by Roux et al 2004 to be accompanied by a 37% recessive fitness cost in a model ('' Arabidopsis thaliana'').

Use in genetic engineering

Genes conveying resistance to chlorsulfuron are used as

selectable marker A selectable marker is a gene introduced into a cell, especially a bacterium or to cells in culture, that confers a trait suitable for artificial selection. They are a type of reporter gene used in laboratory microbiology, molecular biology, a ...

s when attempting transformation with other genes, for example in ''

Dianthus caryophyllus ''Dianthus caryophyllus'' (), commonly known as the carnation or clove pink, is a species of '' Dianthus''. It is likely native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years.M ...

'' and ''

Marchantia polymorpha ''Marchantia polymorpha'' is a species of large thalloid liverwort in the class Marchantiopsida. ''M. polymorpha'' is highly variable in appearance and contains several subspecies. This species is dioicous, having separate male and female plants ...

''. Crops have also been deliberately made resistant, for example in maize/corn by McCabe et al 1988 using bombardment with the relevant gene attached to tungsten particles.

Applications

Chlorsulfuron has a broad spectrum of activity on commercially important broadleaf weeds and grasses but at the recommended use rate it is safe to important crops such as wheat. Its properties mean that it can be applied to soil so emerging weeds take it up and are controlled. Alternatively, spraying after weeds are already present in the crop will also lead to control. The product is used at application rates of . The estimated use in US agriculture is mapped by the US Geological Service and shows that from 1992 to 2017, the latest date for which figures are available, up to were applied each year. The compound is used mainly in wheat but also in pasture. Chlorsulfuron is recommended alone or with aminocyclopyrachlor for control of ''

Centaurea solstitialis ''Centaurea solstitialis'', the yellow star-thistle, is a species of thorny plant in the genus '' Centaurea'', which is part of the family Asteraceae. A winter annual, it is native to the Mediterranean Basin region and invasive in many other ...

'', ''

Centaurea calcitrapa ''Centaurea calcitrapa'' is a species of flowering plant known by several common names, including red star-thistle and purple star thistle. It is native to Europe but is rarely found there, it is known across the globe as an introduced species an ...

'', and ''

Centaurea iberica ''Centaurea iberica'', the Iberian knapweed or Iberian star-thistle, is a species of ''Centaurea''. It is native to southeastern Europe and southwestern Asia. It is known elsewhere as an introduced species and a noxious weed. Control Aminocycl ...

'' in the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Tho ...

of North America.

References

{{herbicides Sulfonylureas Sulfonylurea herbicides Chloroarenes Triazines Methoxy compounds