Tri-allate
Tri-allate or triallate is a selective preëmergent thiocarbamate herbicide, used to control wild oats and sundry grasses and broadleaf weeds, often co-applied with trifluralin, which is much weaker against wild oats than tri-allate. Residual control can be expected for 6 to 8 weeks. It is used in Australia, and the United States. It was first registered in 1961.
In 2001, US agriculture used annually.
Tri-allate is a mitosis-inhibitor; its HRAC classification is Group J, Group K3, Group 15. Affected weeds are prevented from germinating, or their shoots will be swollen and bright green.
Environmental behaviour
Under very dry conditions, tri-allate can persist in soil for several months, and can damage field oats and sorghum. Degradation is dependent on soil microörganisms and moisture levels. Tri-allate is nontoxic to birds and bees, though it is very toxic to aquatic life. It doesn't bioaccumulate in plants, and has low mobility in soil. The aquatic toxicity is most potent against invertebrates and algae. The EPA says "the overall ecological risk associated with the use of triallate is low".The average soil half life is 82 days in "typical" conditions; it is also measured at 46 days, under "field" conditions. Similar half-life is seen in water sediment and in acidic solution.
Properties
Triallate is synthesised from diisopropylamine, phosgene and 2,3,4-trichloro-phenyl-1-thiol. Its surface tension is 0.049 N/m, as a 90% solution at 20 °C. Monsanto manufactured it in the 1960s by the reaction of diisopropylthiocarbamate salt with 1,1,1,3-tetrachloro-propene. It is soluble in acetone, ether, ethyl alcohol, heptane, benzene, ethyl acetate and most organic solvents.Diallate is almost identical, but missing one of triallate's 3 chlorine atoms. Unlike triallate, it has cis- and trans- isomers.
Health
Exposure to large amounts of tri-allate may harm the liver, spleen and kidneys. The EPA considers tri-allate to be a possible carcinogen, the result being "borderline" statistically significant in a trial on mice, though their rough estimate is that the chance of cancer from dietary triallate is one in 14 million. This trial only showed an increased incidence of tumors in one measured category, in a sample size of 15. Diallate, a very similar herbicide, was carcinogenic, possibly prompting the concern for triallate.In tests on rabbits, no fetotoxic or teratogenic effects were observed, although a small decrease of birth weight was strongly evidenced.
Regulatory status
Tri-allate is limited to the US states of California, Colorado, Idaho, Kansas, Minnesota, Montana, Nebraska, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming, as of 2023. In Australia, all states allow it to control wild oats and most allow its broader use in combination with trifluralin. It is used in the United Kingdom, Morocco and the EU states of Belgium, France, Ireland and the Netherlands.Application
It is incorporated to soil pre-sowing or incorporated by sowing, and is applied immediately before or up to 3 weeks before sowing. It is recommended to incorporate it 2–4 cm deep, and within 6 hours if the soil is moist, or 24 hours if dry, to minimise volatilisation. Proper incorporation is essential for efficacy, and two-pass incorporation is needed for maximum efficacy. Efficacy can also be reduced if the top 2 cm of soil is very dry.Tri-allate is applied at 0.8-1.0 kg/Ha in Australia, with a spraywater volume of 30 to 100 L/Ha. Triallate is sold as an emulsifiable concentrate of 500 g/L active ingredient.