Chlormequat

Chlormequat was discovered in the 1950s, and was the first known plant growth regulator. It can cause stem thickening, reduced stem height, additional root development, plant dwarfing, and increase chlorophyll concentration.{{cite journal |last1=Katel |first1=Shambhu |last2=Mandal |first2=Honey Raj |last3=Kattel |first3=Sujata |last4=Yadav |first4=Shubh Pravat Singh |last5=Lamshal |first5=Baibhav Sharma |title=Impacts of plant growth regulators in strawberry plant: A review |journal=Heliyon |date=December 2022 |volume=8 |issue=12 |pages=e11959 |doi=10.1016/j.heliyon.2022.e11959|doi-access=free |pmid=36466575 |pmc=9712129 }}

Chlormequat is an inhibitor of gibberellin biosynthesis, thereby causing reduced cell elongation and thicker sturdier stalks that facilitate harvesting of cereal crops.{{cite book|last1=Gowariker|first1=Vasant|author4=V. N. Krishnamurthy|author2=Kalyani Paranjape|author3=Sudha Gowariker|title=The pesticide encyclopedia|date=2013|publisher=CABI|location=Wallingford|isbn=978-1780640143|page=93}} It can also be used as an adjuvant for herbicides by retarding their oxidative disposal by plants. This is due to cytochrome P450-inhibition.

In the United States, chlormequat is classified as a low risk plant growth regulator and it is registered for use on ornamental plants grown in greenhouses, nurseries, and shadehouses.{{Cite web |title=72 FR 67296 - Chlormequat Chloride Reregistration Eligibility Decision for Low Risk Pesticide; Notice of Availability |url=https://www.govinfo.gov/app/details/FR-2007-11-28/E7-23053 |url-status=live |archive-url=https://web.archive.org/web/20220526041711/https://www.govinfo.gov/app/details/FR-2007-11-28/E7-23053 |archive-date=26 May 2022 |access-date=18 February 2024 |website=GovInfo}} The {{LD50}} (rat, oral) is approximately 670 mg/kg. Exposure to high levels of chlormequat has been linked to developmental toxicity in animal models.{{Cite web | url = http://www.fao.org/docrep/w8141e/w8141e0k.htm | title = Chlormequat | publisher = Food and Agricultural Organization of the United Nations}}{{cite journal |last1= Wang |first1=X |last2=Weidong |first2=H |title= Reproductive and developmental toxicity of plant growth regulators in humans and animals. |journal= Pesticide Biochemistry and Physiology |date=November 2023 |volume=196 |pages=129–33 |pmid= 37945238 |doi= 10.1016/j.pestbp.2023.105640}}

Chlormequat has not previously been registered for use on food crops in the United States. In April 2023, the U.S. Environmental Protection Agency proposed allowing the use of the chemical on food crops such as barley, oat, triticale, and wheat. The EPA’s human health risk assessment indicated "no dietary, residential, or aggregate (i.e., combined dietary and residential exposures) risks of concern." No risks were identified by EPA to aquatic species of invertebrates, vertebrates, and plants in addition to terrestrial plants.{{Cite web |date=2024-04-26 |title= EPA Proposes to Register New Uses of Pesticide Chlormequat Chloride |url=https://www.epa.gov/pesticides/epa-proposes-register-new-uses-pesticide-chlormequat-chloride|access-date=2024-02-16 |website=www.epa.gov |language=en|quote=Before issuing this proposed registration decision, EPA assessed whether exposures to this product would cause unreasonable adverse effects to human health and the environment, as required by the Federal Insecticide, Rodenticide, and Fungicide Act (FIFRA). Based on EPA’s human health risk assessment, there are no dietary, residential, or aggregate (i.e., combined dietary and residential exposures) risks of concern. EPA’s ecological risk assessment identified no risks of concern to non-target, non-listed aquatic vertebrates that are listed under the Endangered Species Act, aquatic invertebrates, and aquatic and terrestrial plants.}}

In July 2022, the EU published Regulation (EU) 2022/1290, which amended the maximum residue levels (MRLs) for chlormequat in or on certain products, based on the scientific assessment of EFSA and the international standards of the Codex Alimentarius Commission. The regulation lowered the MRL for chlormequat in citrus fruits from 2 mg/kg to 0.5 mg/kg, and also modified the MRLs for other products such as apples, pears, quinces, cherries, plums, apricots, and barley. The regulation also set a specific MRL of 0.01 mg/kg for Spodoptera exigua multicapsid nucleopolyhedrovirus (SeMNPV) isolate BV-0004, a biological plant protection product containing chlormequat as a co-formulant. The regulation entered into force on 14 August 2022.{{Cite web |title=Regulation - 2022/1290 - EN - EUR-Lex |url=https://eur-lex.europa.eu/eli/reg/2022/1290/oj |access-date=2024-02-25 |website=eur-lex.europa.eu |language=en}}

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