Diquat

Diquat is an organic dication used as a contact herbicide that produces desiccation and defoliation. It is no longer approved for use in the European Union, but its registration remains valid in many other countries, including the USA.

Synthesis

Diquat is synthesized by oxidatively coupling pyridine to form 2,2'-bipyridine over a heated Raney nickel catalyst, followed by the reaction with 1,2-dibromoethane to form the ethylene bridge.

History

Diquat's herbicidal properties were first recognized in 1955 at Imperial Chemical Industries (ICI) laboratories in England. It was initially used to control broadleaved annual weeds, but its use was later extended to pre-harvest desiccation of oilseed crops.

Use

Diquat is often applied directly to mature crops to cause desiccation, making harvesting easier. It is also used to control invasive species in aquatic environments[2]. The estimated annual use of diquat in US agriculture is around 300,000 pounds, primarily in fruit and vegetable crops.

Human Safety

Diquat dibromide is moderately toxic and may be harmful if swallowed, inhaled, or absorbed through the skin in large quantities. The World Health Organization (WHO) and Food and Agriculture Organization (FAO) have set an acceptable daily intake for diquat.

Mode of Action

Diquat inhibits photosynthesis in plants, causing desiccation and defoliation. It is a fast-acting, non-residual solution that controls weeds in various aquatic environments and is also used in landscapes and other terrestrial applications[3].

Citations:

[1] https://en.wikipedia.org/wiki/Diquat

[2] https://www.lakerestoration.com/product/diquat/

[3] https://alligare.com/product/diquat/

[4] https://aquaplant.tamu.edu/files/2023/08/Diquat.pdf

[5] https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/fs_PC-032201_1-May-02.pdf