Abstract
Pyrazolate [4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-pyrazolyl p-toluenesulfonate] is a wide spectrum herbicide with excellent selectivity in paddy rice. It has proved successful in controlling both annual and perennial weeds including the problem species of Cyperus, Echinochloa and Sagittaria. The Laboratories set up a research project for perennial weeds control in 1971 and started to screen compounds for several weed species. In 1973, a leading compound was found, which was then optimized through extensive derivatization and evaluation of herbicidal spectrum, selectivity to rice plants, toxicity and environmental safety, cost-performance, etc. The compound thus selected, 4-(2, 4-dichlorobenzoyl)-1, 3-dimethyl-5-hydroxypyrazole, was so soluble in water that its direct application into paddy fields gave some unfavorable results in biological performance. Accordingly, the compound was derivatizedto mask the hydroxy group aiming at chemical slow release of the herbicidal entity into paddy water. Among a lot of derivatives, pyrazolate was finally selected for its cost-performance, low toxicity to non-target organisms, low impact to the environment. Pyrazolate, with its extremely low solubility along with high hydrolyzability in water, continuously releases the herbicidal entity into paddy water. Its release rate was further optimized to attain maximum herbicidal effect by means of formulation technology such as micronizations of the crystal particles and granular formulations with which the dispersion of ultrafine particles is suppressed to a certain extent. Since the launch of the single active ingredient preparation (Sanbirde®) in 1980, combination products with many other herbicides manifesting either synergistic or complementary effects have been developed.
