Weed Biology and Management 18, 75–91 (2018) REVIEW PAPER Development of herbicides for paddy rice in Japan KENSHIRO HAMAMURA* 1Japan Association for Advancement of Phyto-Regulators (JAPR), Tokyo, 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 availabil- ity 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 herbi- cides have been improved by using newly developed chemicals with excellent herbicidal effi- cacy, 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 for- mulation, “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 pro- moted and contributed to the development of herbicides through collaboration with agro- chemical 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. Keywords: application methods, development of herbicides, labor-saving technology, one-shot herbicide, weeding hours. INTRODUCTION Jomon era, c.a. 2500 years ago (Watanabe 2011), although a certain word indicating weeding in rice was In Japan, it is believed that “weeding” came into prac- used in a Tanka, a Japanese traditional short poem, tice in rice cultivation along with conversion to trans- around the year 1200 (during the Kamakura period in planting from direct sowing (broadcasting) several Japanese history) (Yabuno & Yamaguchi 2001). Hand centuries after adopting rice cropping, at the end of weeding was carried out manually. As more systematic management practices were developed, weeding was *Correspondence to: Kenshiro Hamamura, Research Institute, Japan Association for Advancement of Phyto-Regulators (JAPR), established as an essential process for every season in 860, Kashiwada, Ushiku, Ibaraki 300-1211, Japan. growing rice crops. In later years, weeding tools, such Email: [email protected] as the “Gandsume” and “rotary paddy weeders” (Fig. 1), were invented, at around 1700 and 1892, respectively, Communicated by H. Kobayashi to improve work efficiency and became a common Received 6 March 2018; accepted 17 May 2018 means for weed control. Although farmers took doi:10.1111/wbm.12147 © 2018 Weed Science Society of Japan 76 K. Hamamura Fig. 1. Rotary paddy weeder (left) and weeding practice with it (right). [Color figure can be viewed at wileyonlinelibrary.com] advantage of such weeding tools in addition to weeding regions and provides approximately 40% of the culti- by hands, it was still very laborious to weed in paddy vated area (STAT 2016). In these regions, because most fields, especially because the work often had to be car- of the cultivable land is naturally sloped, what we ried out under the scorching sun in midsummer. The observe is many small paddy fields. According to the hardship must have been beyond description. survey carried out in 2015 as part of the Paddy Field In 1941, the herbicide 2,4-dichlorophenoxyacetic Improvement Project by the Japanese Ministry of Agri- acid (2,4-D) was discovered and synthesized in the culture, Forestry and Fisheries (MAFF), a field size of USA and was introduced in Japan in 1947. The wide- 0.3 ha can be regarded as the standard, and a field size spread domestic use of the herbicide started in 1950 of 1 ha or larger is considered very large. The 1981 sur- and drastically changed weed control methods in rice vey shows that the average paddy field size was 0.063 (Watanabe 2011). Based on 2,4-D and some other che- ha, and each farmer was, on average, responsible for 8.4 micals, the practice established in the 1970s was the fields (≈0.5 ha). In the 2014 survey, almost 60% of sequential application of herbicides in which multiple paddy fields had been redesigned/laid out so that each types of herbicides, such as early season herbicides (soil- field measured 0.3 ha or larger, of which only 9% were applied), middle season herbicides (foliar- and soil- as large as or larger than 1 ha (MAFF 2016). Because applied) and late season herbicides (foliar-applied), are the average paddy field size was still small, labor-saving used in combination. In the 1980s, many farmers used formulations, which were developed through joint such sequential applications, substantially increasing the research between agrochemical companies and the quantities of herbicides used. To reduce the application Japan Association for Advancement of Phyto- times of herbicides and total amounts of herbicides Regulators (JAPR), were introduced to realize easy used, one-shot herbicides were developed and later manual treatment without using machinery for the became the most commonly used herbicides in paddy application of herbicide. As a result, the time required fields (Takeshita 2004). for weeding in paddy fields was reduced significantly. The development of one-shot herbicides was fol- This report discusses paddy herbicides that have lowed by the introduction of labor-saving formulation been developed in Japan. The topics include changes types, such as “Jumbo” and “Flowable (or suspension in herbicides (chemical compounds) registered to concentrate, SC),” which overtook the preceding types MAFF according to the mode of action, in their prac- of formulations, such as granule (GR), wettable powder tical use over time along with the development of (WP) and emulsifiable concentrate (EC). It has been one-shot herbicides, in the total application area by considered that the availability of various formulation treatment method along with herbicide formulation types might be related to the geographical characteris- types, in the total application area by type of formula- tics and average paddy field size in Japan. Of the total tion and in weeding hours after the development of land area, 70% is classified as hilly and mountainous herbicides. © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 77 16 A B C1 C2 B C3 E F2 F3 Fig. 2. Number of paddy rice 14 K1 K3 L M herbicides based on the year of N O registration in Japan. Classified by 12 HRAC:A,ACCaseinhibitors;B, 10 ALS inhibitors; C1-3, photochem- Z, K3 istry system II inhibitors; E, PPO 8 inhibitors; F2, 4-HPPD inhibitors; O F2 F3,others;K1,microtubuleassem- 6 bly inhibitors; K3, VLCFAE compounds of Chemical E,N inhibitors;L,cellwallinhibitors; 4 C1 M, uncoupling, membrane rup- Number A 2 ture; N, lipid synthesis inhibitors C2 C3,K1 (non-ACCase inhibitors); O, syn- F3 L C2,F3,L,M thetic auxins; Z, unknown com- 0 1987 1967 1975 2003 2007 1959 1981 1983 1985 1993 1995 1997 2013 2017 1965 1969 1971 1973 2005 2009 1945 1947 1949 1953 1955 1957 1977 1989 1991 1999 2001 2015 1961 1963 2011 pounds. [Color figure can be 1951 1979 viewed at wileyonlinelibrary.com] Year DEVELOPMENT OF HERBICIDES AND retracted by 2007. After the introduction of nitrofen in THE AMOUNT OF ACTIVE Group E (PPO inhibitors) in 1963, other Group E com- INGREDIENTS USED pounds, such as chlornitrofen (CNP), fluoronitrofen, oxadiazon and chlomethoxyfen, were also put to practi- Development of paddy herbicides according to cal use. Despite their extensive use as early-season soil- fi the mode-of-action classi cation applied herbicides, they were cancelled one after another Fig. 2 shows the registered number of paddy herbicides because of the problems related to dioxin and dioxin-like based on the year of registration in Japan, and the her- compounds (Masunaga 2000). However, use of other bicides are arranged by the mode of action. The chemi- compounds (pentoxazone and pyraclonil) commenced in cal compounds of herbicides are limited to those used 1998 or afterward, and their effectiveness on broadleaved during the cultivation period of paddy rice and are clas- weeds of sulfonylurea-resistant (SU-R) biotypes of Lin- sified according to the Herbicide Resistance Action dernia procumbens (Krock.) Borbas were well recognized. Committee Group (HRAC 2017). Currently, in Group E, four types of compounds are In 1950, a synthetic auxin, 2,4-D (categorized as widely used. In 1963, prometryn in Group C1 (photo- HRAC Group O), was put to practical use, which was chemistry system II inhibitors) was released commer- followed by the successive release of products with other cially, which was followed by the introduction of other chemical compounds in Group O, such as 2,4-D-trietha- compounds of the same group, such as simetryn and nolamine, 4-chloro-2-methylphenoxyacetic acid-sodium dimethametryn. These are ingredients of middle-season, (MCPA-sodium), 2,4-D-ethyl ester, MCP-ethyl ester foliar- and soil-applied herbicides.