Mesotrione is the
ISO
ISO is the most common abbreviation for the International Organization for Standardization.
ISO or Iso may also refer to: Business and finance
* Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007
* Iso ...
common name for an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...
that is used as a
selective herbicide
Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
, especially in
maize
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
.
A synthetic inspired by the natural substance
leptospermone, it inhibits the enzyme
4-hydroxyphenylpyruvate dioxygenase
4-Hydroxyphenylpyruvate dioxygenase (HPPD), also known as α-ketoisocaproate dioxygenase (KIC dioxygenase), is an Fe(II)-containing non-heme oxygenase that catalyzes the second reaction in the catabolism of tyrosine - the conversion of 4-hydro ...
(HPPD)
and is sold under brand names including Callisto and Tenacity. It was first marketed by
Syngenta in 2001.
History
The invention of the triketone class of herbicides had its beginnings in an observation in 1977 of
allelopathic weed control near a bottlebrush tree, ''
Callistemon citrinus''. Chemists at the
Stauffer Chemical
Stauffer Chemical Company was an American chemical company which manufactured herbicides and pesticides for various agricultural crops. It was acquired by Imperial Chemical Industries from Chesebrough-Pond's Inc. in 1987. In 1987, Stauffer's head ...
Company identified the compound responsible as
leptospermone, a known
natural product which had not previously been reported as having biological activity.
![Leptospermone](https://upload.wikimedia.org/wikipedia/commons/b/bf/Leptospermone.svg)
Extensive work on analogues led to the discovery and development of
sulcotrione and mesotrione.
![Chemical structure of sulcotrione](https://upload.wikimedia.org/wikipedia/commons/2/24/Chemical_structure_of_sulcotrione.png)
The triketone herbicides were found to be effective on a wide range of commercially-important weed species and to have both pre- and post-emergence activity. Mesotrione was chosen for development (by
Zeneca
Zeneca (officially Zeneca Group PLC) was a British multinational pharmaceutical company headquartered in London, United Kingdom. It was formed in June 1993 by the demerger of the pharmaceuticals and agrochemicals businesses of Imperial Che ...
Agrochemicals under the code number ZA1296) because it controls a wide range of broad-leaved weeds that compete with maize and can also suppress some annual grass weeds that may be present in the crop. It achieves this selectivity and lack of damage to the crop owing to its greater potency on the target enzyme found in
dicotyledons than
monocotyledon
Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...
s
and because maize can metabolise the compound in the dione-containing ring.
Synthesis
The synthesis of mesotrione
was first disclosed in patents filed by
ICI, who had acquired Stauffer in 1987.
1,3-Cyclohexanedione is first reacted with the acid chloride of 4-(methylsulfonyl)-2-nitrobenzoic acid under conditions in which the
enol
In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene ( olefin) with a hydroxyl group attached to one end of the alkene double bond (). The t ...
ic hydroxyl group of the diketone reacts to form the
benzoylated derivative. In a separate step, this is rearranged to mesotrione using a catalytic amount of cyanide ion derived from acetone cyanohydrin.
:
Mechanism of action
Mesotrione inhibits the enzyme
4-hydroxyphenylpyruvate dioxygenase
4-Hydroxyphenylpyruvate dioxygenase (HPPD), also known as α-ketoisocaproate dioxygenase (KIC dioxygenase), is an Fe(II)-containing non-heme oxygenase that catalyzes the second reaction in the catabolism of tyrosine - the conversion of 4-hydro ...
(HPPD).
It is an extremely potent inhibitor of HPPD in laboratory tests using the plant ''
Arabidopsis thaliana'', with a K
i value of about 10 pM.
In plants, HPPD is necessary for the
biosynthesis of
tocopherol
Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rat ...
s and of
plastoquinone
Plastoquinone (PQ) is an isoprenoid quinone molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4-benzoquinone m ...
, which is essential to
carotenoid production. Inhibiton of the pathway ultimately leads to bleaching of leaves as
chlorophyll is degraded, followed by plant death.
Formulations
Mesotrione is made available to end-users only in
formulated products. These use non-powdery material with reduced or no use of hazardous solvents, for example suspension concentrates. The herbicide is compatible with other compounds that may be mixed by the farmer to extend control to the grass weeds which mesotrione itself does not kill.
Usage
Mesotrione is a systemic pre- and post-emergence herbicide for the selective contact and residual control of broadleaf weeds in field corn, seed corn, yellow popcorn and sweet corn.
All pesticides are required to seek
registration
Register or registration may refer to:
Arts entertainment, and media Music
* Register (music), the relative "height" or range of a note, melody, part, instrument, etc.
* ''Register'', a 2017 album by Travis Miller
* Registration (organ), th ...
from appropriate authorities in the country in which they will be used.
In the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...
, the
Environmental Protection Agency (EPA) is responsible for regulating pesticides under the
Federal Insecticide, Fungicide, and Rodenticide Act
The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) is a United States federal law that set up the basic U.S. system of pesticide regulation to protect applicators, consumers, and the environment. It is administered and regulated by th ...
(FIFRA) and the
Food Quality Protection Act
The Food Quality Protection Act (FQPA), or H.R.1627, was passed unanimously by Congress in 1996 and was signed into law by President Bill Clinton on August 3, 1996. The FQPA standardized the way the Environmental Protection Agency (EPA) would man ...
(FQPA).
A pesticide can only be used legally according to the directions on the label that is included at the time of the sale of the pesticide. The purpose of the label is "to provide clear directions for effective product performance while minimizing risks to human health and the environment". A label is a legally binding document that mandates how the pesticide can and must be used and failure to follow the label as written when using the pesticide is a federal offence.
Within the European Union, a 2-tiered approach is used for the
approval and authorisation of pesticides. Firstly, before a formulated product can be developed for market, the active substance must be approved for the European Union. After this has been achieved, authorisation for the specific product must be sought from every Member State that the applicant wants to sell it to. Afterwards, there is a monitoring programme to make sure the pesticide residues in food are below the limits set by the
European Food Safety Authority
The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...
.
Agricultural use
![Mesotrione use USA](https://upload.wikimedia.org/wikipedia/commons/3/30/Mesotrione_use_USA.png)
Mesotrione possesses a broad spectrum of activity on commercially important broadleaf weeds including ''
Abutilon theophrasti
''Abutilon theophrasti'' (velvetleaf, velvet plant, velvetweed, Chinese jute, China jute, crown weed, buttonweed, lantern mallow, butterprint, pie-marker, or Indian mallow) is an annual plant in the family Malvaceae, native to southern Asia.
It ...
'', ''
Amaranthus powellii'', ''
Amaranthus retroflexus
''Amaranthus retroflexus'' is a species of flowering plant in the family Amaranthaceae with several common names, including red-root amaranth, redroot pigweed, red-rooted pigweed, common amaranth, pigweed amaranth, and common tumbleweed. page 4 ...
'', ''
Chenopodium album
''Chenopodium album'' is a fast-growing weedy annual plant in the genus ''Chenopodium''. Though cultivated in some regions, the plant is elsewhere considered a weed. Common names include lamb's quarters, melde, goosefoot, wild spinach and fat-h ...
'', ''
Datura stramonium
''Datura stramonium'', known by the common names thorn apple, jimsonweed (jimson weed), devil's snare, or devil's trumpet, is a poisonous flowering plant of the nightshade family Solanaceae. It is a species belonging to the ''Datura'' genus a ...
'', ''
Digitaria sanguinalis
''Digitaria sanguinalis'' is a species of Poaceae, grass known by several common names, including hairy crabgrass, hairy finger-grass, large crabgrass, crab finger grass, purple crabgrass. It is one of the better-known species of the genus ''Digi ...
'', ''
Lamium purpureum
''Lamium purpureum'', known as red dead-nettle, purple dead-nettle, or purple archangel, is an annual herbaceous flowering plant native to Europe and Asia.
Varieties:
* ''Lamium purpureum'' var. ''hybridum'' (Vill.) Vill. (synonym: ''Lamium hybr ...
'', ''
Polygonum persicaria'', ''
Rumex crispus'', ''
Senecio vulgaris
''Senecio vulgaris'', often known by the common names groundsel and old-man-in-the-spring, is a flowering plant in the family Asteraceae. It is an annual herb, native to Europe and widely naturalised as a ruderal species in suitable disturbed ha ...
'', ''
Solanum nigrum'', ''
Stellaria media'' and ''
Xanthium strumarium
''Xanthium strumarium'' (rough cocklebur, clotbur, common cocklebur, large cocklebur, woolgarie bur) is a species of annual plants of the family Asteraceae. Some sources claim it originates in southern Europe and Asia, but has been extensively na ...
''. In addition, 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.
This combination of properties has meant that mesotrione achieved widespread use very quickly and reached annual sales of more than $400 million by 2011.
The product is used at application rates of 75-150 g/ha.
The estimated annual use of mesotrione in US agriculture is mapped by the US Geological Service and shows an increasing trend from its introduction in 2001 to 2018, the latest date for which figures are available and now reaching . As would be expected for a compound used almost exclusively in maize, the heaviest use is in the
corn belt
The Corn Belt is a region of the Midwestern United States that, since the 1850s, has dominated corn production in the United States. In the United States, ''corn'' is the common word for maize. More generally, the concept of the Corn Belt con ...
.
Human safety
The
LD50 of mesotrione is over 5000 mg/kg (rats, oral),
which means that it is practically non-toxic by oral ingestion, but it can cause serious eye irritation. First aid information is included with the label.
The
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...
(WHO) and
Food and Agriculture Organization
The Food and Agriculture Organization of the United Nations (FAO)french: link=no, Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is an intern ...
(FAO) joint meeting on pesticide residues has determined that the
acceptable daily intake for mesotrione is 0-0.5 mg/kg bodyweight.
The
Codex Alimentarius database maintained by the FAO lists the maximum residue limits for mesotrione in various food products, most of which are set at its 0.01 mg/kg limit of detection.
Effects on the environment
Mesotrione is very toxic to aquatic life with long lasting effects.
Its
ecotoxicology
Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, which integrates toxicology and ecology ...
is summarised in the Pesticide Properties database.
Resistance Management
Reports of individual weed species, for example ''
Amaranthus tuberculatus
''Amaranthus tuberculatus'', commonly known as roughfruit amaranth, rough-fruited water-hemp, tall waterhemp, or common waterhemp, is a species of flowering plant. It is a summer annual broadleaf with a germination period that lasts several mont ...
'', becoming resistant to mesotrione are monitored by manufacturers, regulatory bodies such as the EPA and the Herbicides Resistance Action Committee (HRAC). In some cases, the risks of resistance developing can be reduced by using a mixture of two or more herbicides which each have activity on relevant weeds but with unrelated mechanisms of action. HRAC assigns active ingredients into classes so as to facilitate this.
Brands
By international convention and in many countries the law, pesticide labels are required to include the common name of the active ingredients. These names are not the exclusive property of the holder of any patent or
trademark
A trademark (also written trade mark or trade-mark) is a type of intellectual property consisting of a recognizable sign, design, or expression that identifies products or services from a particular source and distinguishes them from othe ...
and as such they are the easiest way for non-experts to refer to individual chemicals. Companies selling pesticides normally do so using a brand name or
wordmark
__notoc__
A wordmark, word mark, or logotype, is usually a distinct text-only typographic treatment of the name of a company, institution, or product name used for purposes of identification and branding. Examples can be found in the graphic iden ...
which allows them to distinguish their product from competitor products having the same active ingredient. In many cases, this branding is country and formulation-specific so there can be multiple brand names for a given active ingredient. Mesotrione may be pre-mixed with other herbicides to provide more complete weed control. For example, Acuron is the name used by
Syngenta for a mixture containing bicyclopyrone,
atrazine
Atrazine is a chlorinated herbicide of the triazine class. It is used to prevent pre-emergence broadleaf weeds in crops such as maize (corn), soybean and sugarcane and on turf, such as golf courses and residential lawns. Atrazine's primary manu ...
and
S-metolachlor in addition to mesotrione.
Brand names for mesotrione include Callisto, Instigate, Meristo, Resicore and Tenacity. Suppliers and brand names in the United States are listed in the National Pesticide Information Retrieval System.
See also
*
Nitisinone (orfadin)
References
Further reading
*
*
External links
*
{{herbicides
Herbicides
Benzosulfones
Nitrobenzenes
Triketones
Cyclohexanes
Aromatic ketones