Development of herbicides for paddy rice in Japan

The history of the development of herbicides for mechanized paddy rice production in Japan can be characterized by a combination of products with several ingredients, by large availability in formulation, and by application methods for labor saving in accordance with natural and social conditions of the country, for instance, around 40% of national land located in hilly and mountainous areas, small size paddy fields consolidated in approximately 0.3 ha on average and so on. As for combination products, one‐shot herbicides that can control both annual and perennial weeds, including grasses, sedges and broadleaved weeds, mainly with sulfonylureas have been a major means of rice production since the 1980s. One‐shot herbicides have been improved by using newly developed chemicals with excellent herbicidal efficacy, such as acetolactate synthase (ALS), 4‐hydroxyphenylpyruvate dioxygenase (4‐HPPD), protoporphyrinogen oxidase (PPO) and very‐long‐chain fatty acid elongase (VLCFAE) inhibitors, and by combining ingredients that are effective against sulfonylurea‐resistant (SU‐R) biotypes of lowland weeds. The latest type of one‐shot herbicides can control noxious species such as Eleocharis kuroguwai as well as other ordinal species. Regarding herbicide formulation, “1 kg granule,” “Jumbo,” “Flowable,” “Diffusion granule” and so on have been developed to save farmers the troubles of applying herbicides. As for application methods, “at‐transplanting application,” “at‐irrigation inlet application” and utilization of radio‐controlled helicopters or boats were put into practical use as labor‐saving technology. As a result, farmers were spared the severe hand‐weeding work under blazing heat during the summer season. Japan Association for Advancement of Phyto‐Regulators (JAPR) have promoted and contributed to the development of herbicides through collaboration with agrochemical companies and research organizations since it was founded in 1964. In this paper, I explain the development progress of herbicide using materials on the mode of action, the trend of one‐shot herbicides, the feature of a labor‐saving formulation and the working hours for weed management in rice production.