Trifluralin is a commonly used pre-emergence herbicide. With about 14e6lb used in the United States in 2001,[1] and NaNe6lb in 2012,[2] it is one of the most widely used herbicides. Introduced in 1964, Trifluralin was the first organofluorine compound used as an agrochemical.
Trifluralin is generally applied to the soil to control annual grass and broadleaf weed species. It inhibits root development by interrupting mitosis and thus can control weeds as they germinate.[3] Trifluralin is also used in Australia, to be applied at 0.8-3.0 L/ha (for a 480 g/L formulation).[4]
Selective herbicides were unavailable in the 1950s to protect soybean and cotton (2,4-DNP could have been used but had to be exactingly applied lest it destroy the crops), so Lilly Research Laboratories screened ~2000 compounds from 1958 to 1980 blindly looking for a result. Trifluralin was initially thought a failure, yet the plots stayed free of weeds weeks later.[5] Application by incorporation into the top soil instead was eight times more potent.[6] Pre-plant soil incorporation was a new technique at the time. It is unclear why trifluralin's exotic 4-trifluoromethyl was tested so early (1960), before more common candidates such as fluoro, bromo, or iodo.[5]
Trifluralin has been banned in the European Union since 20 March 2008, primarily due to high toxicity to aquatic life.[7]
Trifluralin is on the United States Environmental Protection Agency list of Hazardous Air Pollutants as a regulated substance under the Clean Air Act.[8]
Trifluralin breaks down into many products as it degrades, ultimately being incorporated into soil-bound residues or converted to carbon dioxide (mineralized). Among the more unusual behaviors of trifluralin is inactivation in wet soils. This has been linked to transformation of the herbicide by reduced soil minerals, which in turn had been previously reduced by soil microorganisms using them as electron acceptors in the absence of oxygen. This environmental degradation process has been reported for many structurally related herbicides (dinitroanilines) as well as a variety of explosives such as TNT and picric acid.[9]
Trifluralin has a long half-life in soil of ~180 days, but it is accepted at high application rates because of its low soil mobility and high volatility.[5] It is safe for mammals and chickens, even in large amounts.[10]