Development of Herbicides for Paddy Rice in Japan

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 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 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 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.

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. In 1966, bensulide in and 2-methyl-4-chlprophenoxyaceto-0-chloroanilide Group N (lipid synthesis inhibitors, non-acetyl- (MCPCA). In 1969, the number of Group-O com- coenzyme A carboxylase (non-ACCase) inhibitors) pounds in use peaked at 14. Of these, six compounds became available, and two other compounds of the same were removed from the list by 1985. Currently, seven group (thiobencarb and molinate) were added to the list are still available. In 1960, pentachlorophenol-calcium in 1969 or afterward. Currently, four compounds are (PCP-Ca) in Group M (uncoupling, membrane rupture) used as ingredients of middle-season, foliar and soil- became commercially available and was widely used applied herbicides, which are mostly for the control of because of its effectiveness on Echinochloa spp. The addi- Echinochloa spp. In Group K3 (VLCFAE inhibitors), start- tion of another compound, PCP-hydrazine, in 1966 ing with the practical application of butachlor in 1973, increased the number of Group M compounds on the list other compounds such as piperophos, naproanilide, pre- to two. However, because they were toxic to fish, both tilachlor, mefenacet, anilofos and fentrazamide were also were invalidated by 1976 (Yoshizawa 1995). In 1961, made available commercially. Currently, eight com- propanil in Group C2 (photochemistry system II inhibi- pounds are used as ingredients of one-shot herbicides to tors) was allowed for practical application, and in 1976, mainly control Echinochloa spp. In 1975, bentazone in fluothiuron, of the same group, was added. Both were Group C3 (photochemistry system II inhibitors) was © 2018 Weed Science Society of Japan 78 K. Hamamura

60 B Z K3 O F2 E N C1 ⇐ A : ACCase inhibitors A C3 K1 C2 F3 L M ⇐ C1 : Photochemistry systemϩinhibitors 50 ⇐ N : Lipid synthesis inhibitors (non-ACCase inhibitors) ⇐ E: PPO inhibitors 40 ⇐ F2: 4-HPPD inhibitors

⇐ O: Synthetic auxins 30 ⇐ K3: VLCFAE inhibitors

20 ⇐ Z : Unknown compounds Number of Chemical compounds 10 ⇐ B : ALS inhibitors

0 1950 1960 1970 1980 1990 2000 2010 2015 Year Fig. 3. Number of paddy rice herbicides based on the year of registration in Japan. [Color figure can be viewed at wileyonlinelibrary.com] allowed for commercial use, and 10 years later, Group B, other compounds, such as pyrazosulfuron-ethyl, bentazone-sodium was also included. imazosulfuron, halosulfuron-methyl, cyclosulfamuron, Although these are the only two compounds available azimsulfuron, pyriminobac-methyl, bispyribac-sodium, in Group C3, they are very effective on large perennial pyriftalid, penoxsulam, propyrisulfuron, pyrimisulfan, weeds (excluding Echinochloa spp.) and are, therefore, metazosulfuron and triafamone, were added to the list widely used as the main ingredients of late-season foliar- afterward. Currently, a total of 15 compounds are in use, applied herbicides. With regard to Group F2 (4-HPPD which exceeds the number of compounds available in any inhibitors), pyrazolate became practically applicable in other groups (FAMIC 2017). Each compound of Group 1980. At that time, a widespread infestation of Sagittaria B is able to control specific weeds, so mixing with com- pygmaea Miq. occurred. Because of its high efficacy pounds of other groups creates distinctive herbicides. As a against this species, pyrazolate was introduced as an compound of Group A (ACCase inhibitors), cyhalofop- ingredient in the first products of one-shot herbicides butyl was introduced in 1996. Since then, it has remained (JAPR 1995; Yoshizawa 1995). The other Group-F2 the only compound available in this group. The com- compounds added in the following years included pyra- pound acts specifically on Echinochloa spp. and is effective zoxyfen, benzofenap, benzobicyclon, mesotrione and when applied as foliar treatment. Therefore, it is often tefuryltrione. Eight compounds of Group F2 are cur- used as an herbicide for late-season application, but it is rently in use. All of these exhibit an excellent herbicidal also sold as a combination product to extend the treatment activity against broadleaved weeds such as Monochoria period of one-shot herbicides. Since the introduction of vaginalis var. plantaginea (Burm. f.) Kunth and Lindernia this compound, no more groups have been added to procumbens (Krock.) Borbas. Because some of these com- the list in Japan (Takeshita 2004, Food and Agricultural pounds are also effective on Scirpus juncoides Roxb. var. MaterialsInspectionCenter(FAMIC)2017).Fig.3isa ohwianus T. Koyama, they are used in one-shot herbi- stacked bar chart based on the same data as Fig. 2. In cides to control SU-R biotypes of lowland weeds. In 2015, the ALS inhibitor had the largest number of regis- 1987, bensulfuron-methyl in Group B (ALS inhibitors) trations. The other groups are, in decreasing order in was made available commercially. Having a superior the number of compounds belonging to the group, residual activity in addition to the effectiveness on a unknown compounds of mode of action, VLCFAE inhib- variety of weed species, it soon became widely used itors, synthetic auxins, 4-HPPD inhibitors and PPO as an important ingredient of one-shot herbicides. In inhibitors. © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 79

12000

10000

8000 Total amounts of active ingredients

6000 (× 1,000ha)

䠽䡎䡁䠽㻌 4000

Rice cropping area

Fig. 4. Change in the total amount 2000 of active ingredients used for paddy Rice cropping amounts of active ingredients (×1,000kg a.i./) Total herbicides and rice cropping area in 0 Japan. [Color ﬁgure can be viewed at 1983 1986 1989 1992 1995 1998 2001 2004 2007 2010 2013 wileyonlinelibrary.com]

Amounts of active ingredients used according the total paddy area in Japan. However, with the use of to the mode of action mechanical rice transplanters, the timing of seedling transplanting shifted from the 4–6 leaf stage (grown As of December 2017, a total of 61 compounds in seedlings) to the 2–3 leaf stage (young seedlings), caus- 11 groups, including Group Z, are used as ingredients of ing a critical problem in weed control, namely, an paddy herbicides in Japan (FAMIC 2017). Fig. 4 shows extended period of weed control that arose from the the chronological change in the amounts of these ingredi- delay in the creation of shade from standing rice plants ents used in paddy fields; it was compiled by JAPR as part to stunt weed growth (Watanabe 2011). Another issue of the “survey on herbicide shipments” using the data was the prevalence of perennial weeds in many regions, annually provided by agrochemical companies. The graph partly resulting from the insufficient efficacy of the used peaks in 1984. At that time, as the total area cultivated for herbicides. Another factor was the lack of tillage in paddy rice amounted to nearly 2,300,000 ha, the approxi- autumn, failing to cause the natural death of vegetative mated quantity of ingredients used per hectare was 5 kg. organs. An increasing number of perennial weeds led In 1987, the development of ALS inhibitors (Group B), many farmers to adopt sequential herbicide applications. which are very active in small quantities against paddy As sequential applications involved a combined use of weeds, promptly reduced the amounts of active ingredi- multiple types of herbicides (e.g., soil-applied, soil- and ents used in the following 10 years. After that, the reduc- foliar-applied and foliar-applied), the number of herbi- tion became less prominent, but the amount of active − cide treatments increased to the extent that the esti- ingredients used in 2015 was almost as low as 2 kg ha 1, mated total application area of herbicides was nearly which is approximately 40% that of 1984. ALS inhibitors twice as large as the actual rice cropping area. The orig- have been a preferable choice and are expected to remain inal purpose of weed control is to prevent weeds dam- so in the coming years (Takeshita 2004). aging crops. If the focus is placed on maintaining a certain level of rice production, there should be no problems with the presence of some weeds that cause DEVELOPMENT OF ONE-SHOT no harm in terms of crop yields and quality. However, HERBICIDES AND CHANGE IN TOTAL this was not the only issue farmers had to take care APPLICATION AREA BASED ON of. From their experience, they knew that once they TREATMENT METHOD allowed weeds to grow (no matter how small the amount it might be), future weed management would Development of one-shot herbicides be extremely difficult. To wipe out weeds, they were Basic research on one-shot herbicides was commenced willing to weed by hand despite the arduousness by JAPR in 1975 (JAPR 1984; Yoshizawa 1995), involved. Against such a backdrop of the raising levels which coincided with the rapid spread of mechanical of chemicals in the environment because of the rice transplanters, which were used in almost 60% of increased number of herbicide applications, JAPR © 2018 Weed Science Society of Japan 80 K. Hamamura

7000 Middle or Late stage herbicides (Foliar and Soil-applied or Foliar-applied)

Early stage herbicides (Soil-applied) 6000 One-shot herbicides

Rice cropping area 5000

4000

3000

Rice cropping area (1,000ha) 2000 Total application area (1,000ha)

1000 Fig. 5. Change in the total appli- 0 cation area by treatment method 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 in Japan. [Color figure can be Year viewed at wileyonlinelibrary.com] sought to establish a method that could bring the herbi- with an extended treatment period (which remains cide overdose to an end and minimize the environmen- applicable until the four leaf stage of Echinochloa spp. tal impact. In other words, our goal was to find a such as Echinochloa oryzicola Vasing.), those with longer methodology for the effective application with mini- lasting effects, those acting on common perennial weeds mized doses of herbicides. Thus, new herbicides with (excluding Cyperus serotinus Rottb. and Sagittaria pyg- improved systematic treatment were developed and maea Miq.) and those that can kill SU-R biotypes of made widely available under the name of “one-shot lowland weeds (Hamamura 2011; Watanabe 2011). For herbicides” (JAPR 1984; Yoshizawa 1995). efficient use of one-shot herbicides, it is important to The first one-shot herbicides were launched in 1982. understand their characteristics prior to use and select They were premixed herbicides of naproanilide and the type suitable for the conditions of a given field. butachlor GRs, pyrazolate and butachlor GRs or pyra- Generally, even with the latest one-shot herbicides, sta- zolate and thiobencarb GRs. New compounds were ble control of weeds is difficult to achieve in fields with developed later one after another, including those a high water reaching down, extremely overgrown highly effective on Echinochloa spp. and ALS inhibitors weeds or long-established stands of weeds. If this is the (e.g., bensulfuron-methyl), which can wither/kill a case, one-shot herbicides should be used in combina- variety of weed species through small doses. Many new tion with early-, middle- or late-season herbicides in types of one-shot herbicides containing these new com- conventional sequential applications (Hamamura pounds were released, and prompt spread of their use 2015a). was achieved (Fig. 5). Recent trend of one-shot herbicides Use of one-shot herbicides Over the years, problematic weed species have varied One-shot herbicides are required to be effective against with the history of applied herbicides, usage and crop- annual weeds and two or more species of perennial ping system. Table 1 summarizes the recent weed infes- weeds, with the residual effectiveness of 40–50 days or tations based on the results of the nationwide JAPR the effects lasting until midseason drainage. The efficacy 2009 questionnaire survey on weeds. Some of the weed of one-shot herbicides is assessed based on this criterion. species listed in the table can be completely controlled The one-shot herbicides released in recent years can if sufficient care is given to cropping conditions through provide various extra advantages in addition to the appropriate water management in conjunction with requirements mentioned above. For example, some can herbicides. Retrospective examination of the results of be applied on rice paddies immediately after transplant- past questionnaires indicates a gradual increase of infes- ing (at-transplanting application) because of their high tation levels among difficult-to-control perennial safety levels (Hamamura 2015e). Others include those weeds, such as Sagittaria trifolia L., Eleocharis kuroguwai © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 81

§ Table 1. Problematic weed species based on the results of the JAPR 2009 questionnarie

Category Species

Echinochloa spp. Echinochloa oryzicola Vasing., Echinochloa crus-galli (L.) P.Beauv. var. crus-galli, Echinochloa crus-galli (L.) P.Beauv. var. formosensis Ohwi. Weeds entering from paddy levees Murdannia keisak (Hassk.) Hand.-Mazz., Paspalum distichum L., Leersia japonica (Honda) Makino ex Honda., Leersia oryzoides (L.) Sw. Leptochloa chinensis (L.) Nees. Large weeds growing in shallow water depth Aeschynomene indica L., Bidens frondosa L., Bidens tripartita L. Difﬁcult-to-control perennial weeds Sagittaria trifolia L., Eleocharis kuroguwai Ohwi., Scirpus maritimus L., Scirpus nipponicus Makino. † ‡ SU-resistant weeds Lindernia spp. , Scirpus spp. , Monochoria vaginalis (Burm. f.) Presl var. plantaginea (Roxb.) Solms-Laub., Monochoria korsakowii Regel et Maack, Sagittaria trifolia L. Alisma canaliculatum A. Br. et Bouche, etc.

† Lindernia procumbens (Krock) Borbas), Lindernia dubia var. major Pennell, Lindernia dubia var. dubia Pennell, etc. ‡ Scirpus juncoides Roxb. var. ohwianus T. Koyama, Scirpus wallichii Nees in Wight. § This investigation is aimed at paddy ﬁelds where herbicides are used.

Ohwi., Scirpus maritimus L. and Scirpus nipponicus outcome in 40–50 days after transplanting in the case of Makino (Hamamura 2015a). Although many of the Scirpus juncoides Roxb. var. ohwianus T. Koyama, registered one-shot herbicides are intended to target Cyperus serotinus Rottb., Sagittaria pygmaea Miq. and these species, their efficacy is approved on the condition annual weeds such as Echinochloa spp., and in that they are used in combination with early-, middle- 70–80 days after transplanting in the case of difficult- or late-season herbicides. Their product labels also indi- to-control perennial weeds. Table 2 lists the herbicides cate this requirement for use. The increase of these approved for practical use in 2014. They are expected weed species is considered to be caused by strict restric- to greatly contribute to the better control of difficult- tions on the number of herbicide applications used to to-control perennial weeds (Hamamura 2015a). realize a cropping system with minimal use of pesticides. Application area of one-shot herbicides Recently developed one-shot herbicides are highly active because of the improved herbicidal activity of Fig. 5 shows the chronological change in the total ingredients, effective combination products and application area of paddy herbicides by treatment advanced technologies for herbicide preparation. More- method from 1950, which was the starting year of over, new ingredients that are extremely active against 2,4-D use. Starting from approximately 3,000,000 ha, difficult-to-control perennial weeds (mainly ALS inhib- the total area of rice cropping grounds reached a peak itors such as propyrisulfuron and triafamone) have been of nearly 3,170,000 ha in 1969, with a 100% self- discovered. Targeting weed species with increasing sufficiency rate in rice. However, when it came to the populations, such as Sagittaria trifolia L., Eleocharis kurogu- annual consumption of rice, it was gradually declining, wai Ohwi., Scirpus maritimus L. and Scirpus nipponicus with more bread being introduced to daily meals. Makino., JAPR developed “one-shot herbicides for Under such circumstances, the rice production levels difficult-to-control perennial weeds” with an expected started to be regulated in 1969, and accordingly, less efficacy as high as sequential applications. Since 2013, and less land was cultivated for rice (as shown in Fig. 5, demonstration testing has been under way (JAPR approximately 2,400,000 ha in 1980, approximately 2014). The requirements for one-shot herbicides for 2,100,000 ha in 1990 and approximately 1,600,000 ha difficult-to-control perennial weeds are: (i) targeting in 2015). Next, the change in the total application area one or more species of difficult-to-control perennial over time will be examined based on the treatment weeds, (ii) proven efficacy through testing in a field method in the chronological order of herbicide devel- with naturally grown weeds and (iii) satisfactory opment. Foliar-applied herbicides, which first became © 2018 Weed Science Society of Japan 82 08We cec oit fJapan of Society Science Weed 2018 ©

Table 2. List of herbicides approved for practical use for difﬁcult-to-control perennial weeds in 2014 .Hamamura K. † ‡ Chemical compounds Application Application timing Growing stage of difﬁcult-to-control perennial weeds and content rate (/0.1 ha) Sagittaria Eleocharis Scirpus trifolia L. kuroguwai Ohwi. maritimus L.

Pyraclonil: 5% + propyrisulfuron: 40 g × 3 days after transplanting – Pre- and 2.25% + bromobutide: 22.5% 10packs 3 Leaf stage of Echinochloa spp. postemergence Jumbo Pyraclonil: 3.7% + propyrisulfuron: 500 mL 3 days after transplanting – Pre- and 1.7% + bromobutide: 16.8% 3 Leaf stage of Echinochloa spp. postemergence Flowable Pyraclonil: 2% + propyrisulfuron: 1 kg Just after rice transplanting – Pre- and 0.9% + bromobutide: 9% 3 Leaf stage of Echinochloa spp. postemergence 1-kg granule Triafamone: 0.5% + tefuryltrione: 3.0% 1 kg 5 days after rice transplanting – Pre-emergence – Pre-emergence – Postemergence – 1 kg granule 3.5 Leaf stage of Echinochloa spp. middle stage middle stage middle stage (spatula-like (plant height (plant height leaf stage) of 10 cm) of 30 cm) Triafamone: 0.97% + tefuryltrione: 5.8% 500 mL 5 days after rice transplanting – Pre-emergence – Pre-emergence – Postemergence – Flowable 3.5 Leaf stage of Echinochloa spp. middle stage middle stage middle stage (spatula-like (plant height (plant height leaf stage) of 10 cm) of 30 cm) Triafamone: 1.6% + tefuryltrione: 10% 30 g × 5 days after transplanting – Pre-emergence – Pre- and Postemergence – Jumbo 10 packs 3 Leaf stage of Echinochloa spp. juvenile stage postemergence middle stage (2 leaf stage) (plant height of 25 cm) Propyrisulfuron: 3% + bromobutide: 30 g × 3 days after transplanting – Pre- and 30% + pentoxazone: 6.67% 10 packs 3 Leaf stage of Echinochloa spp. postemergence Jumbo Propyrisulfuron: 1.7% + bromobutide: 500 mL 3 days after transplanting – Pre- and 16.8% + pentoxazone: 3.7% 3 Leaf stage of Echinochloa spp. postemergence Flowable Propyrisulfuron: 0.9% + bromobutide: 1 kg Just after rice transplanting – Pre- and 9% + pentoxazone: 2% 3 Leaf stage of Echinochloa spp. postemergence 1 kg granule Table 2. Continued † ‡ Chemical compounds Application Application timing Growing stage of difﬁcult-to-control perennial weeds and content rate (/0.1 ha) Sagittaria Eleocharis Scirpus trifolia L. kuroguwai Ohwi. maritimus L.

Propyrisulfuron: 4.5% + 20 g × 3 days after transplanting – Pre- and pentoxazone: 10% 10 packs 3 Leaf stage of Echinochloa spp. postemergence Jumbo Propyrisulfuron: 1.7% + 500 mL 3 days after transplanting – Pre- and pentoxazone: 3.9% 3 Leaf stage of Echinochloa spp. postemergence Flowable Propyrisulfuron: 0.9% + pentoxazone: 2% 1 kg Just after rice transplanting – Pre-emergence – 1 kg granule 3 Leaf stage of Echinochloa spp. middle stage (plant height of 10cm) Cyclopyrimorate: 3% + pyrazolate: 1 kg Just after rice transplanting – Pre- and Pre- and 6% + propyrisulfuron: 0.9% 3 Leaf stage of Echinochloa spp. postemergence postemergence

1 kg granule Japan in herbicides paddy of Development Cyclopyrimorate: 5.5% + pyrazolate: 500 mL 5 days after transplanting – pre-emergence – Pre- and 08We cec oit fJapan of Society Science Weed 2018 © 11% + propyrisulfuron: 1.65% 3 Leaf stage of Echinochloa spp. juvenile stage postemergence Flowable (2 leaf stage) Cyclopyrimorate: 8.6% + pyrazolate: 35g × 10 packs 5 days after transplanting – Pre- and Pre- and 17.1% + propyrisulfuron: 2.57% 3 Leaf stage of Echinochloa spp. postemergence postemergence Jumbo

† Application timing mentions the biggest width and does not mention soil character and cultivation time. ‡ Growing stage indicates effective timing to be controlled, and blank column indicates non-consideration. 83 84 K. Hamamura available in 1950, continued to increase the total appli- coincided with the introduction of at-transplanting cation area until 1975, with a peak of approximately application practices, which resulted in frequent use of 1,000,000 ha. The subsequent moderate decline led to one-shot herbicides as an alternative to conventional the lowest level in 1993, after which the total applica- soil-applied herbicides. The total application area of tion area gradually recovered to approximately one-shot herbicides in 2015 was 1,742,000 ha, account- 450,000 ha in 2015 (data omitted). The possible reasons ing for approximately 60% of the total application area for this recovery include an incident of SU-R biotype of all paddy herbicides (2,964,000 ha) (Hamamura weeds in 1997, which was followed by a series of simi- 2015a). lar incidents across the country and common practices of at-transplanting herbicide applications (Hamamura 2015a). HERBICIDE FORMULATIONS AND THE On the other hand, soil-applied herbicides showed a APPLICATION AREA marked increase in the total application area after their The first paddy herbicides were mainly available in fi rst release in 1958, reaching a total application area as either a formulation type of WP or GRs (3kg-GR). fi large as the total hectarage of all paddy elds in 1970. Since 1990, however, a variety of labor-saving formula- After the peak of approximately 3,000,000 ha in 1974, tions have been introduced, including suspension con- the total application area decreased in accordance with centrate (SC or Flowable), 1 kg-granule (1kg-GR), fi the decreasing hectarage of paddy elds (Takeshita water-dispersible granule (WDG), diffusion GRs and 2004). The decline in the total application area became Jumbo (Takeshita & Noritake 2001). Described below prominent especially after 1982, when one-shot herbi- are the characteristics and usage of major types of labor- cides were launched, and produced the lowest value in saving formulations. All the numeric values in this 1997. However, sequential applications of herbicides report were estimated based on the JAPR’s “survey on regained attention as a measure against SU-R biotype herbicide shipments” among agrochemical companies. weeds, which spurred the use of soil incorporation her- As a paddy field of 0.1 ha is considered the standard bicides. Combined with soil incorporation herbicides unit of area in Japan, each product package contains the released after 1972, the total application area amounted quantity of herbicides to be applied to a field of 0.1 ha. to approximately 600,000 ha in 2015. For foliar- and soil-applied herbicides, the total application area rose Jumbo immediately after their launch in 1968, reaching a peak Background information on the development of Jumbo and of approximately 2,000,000 ha in 1977 (data omitted). its practical use Despite the reduction of rice paddy hectarage, this increase in their total application area was made possible “Jumbo” is a type of formulation that JAPR developed by the establishment of their sequential application in to realize the ultimate labor-saving performance and combination with soil-applied herbicides, which indi- cost effectiveness in herbicides (Takahashi et al. 1996). cates the effective utilization of herbicides to improve In September 1990, many agrochemical companies rice production techniques. However, the total applica- were engaged in developing such easy-to-use herbicides tion area started to drop from 1981 and, with less under the name of “throw-in type herbicides.” In change after 1998, became approximately 174,000 ha 1992, demonstration tests were carried out in JAPR’s in 2015 (data omitted). That is, the total application research institute and experimental stations as well as area of middle- or late-stage herbicides (total with other research organizations, which led to the registra- foliar-applied) is approximately 600,000 ha, which is tion of two types of Jumbo formulations (daimuron + almost the same as early stage herbicides (soil-applied) pyributicarb + bensulfuron-methyl Jumbo and quino- in 2015. The major cause for this reduction was the clamine Jumbo) (Koura et al. 1994a,b) on 28 September release of one-shot herbicides in 1982. They took the 1994. Their total application area reached nearly place of soil-applied or foliar and soil-applied herbi- 250,000 ha in 5 years after the launch and 300,000 ha cides, expanding the total application area up to a peak in 10 years. With a rate of increase of almost 20,000 ha of approximately 2,400,000 ha in 1995, which per year after the 10th year, it amounted to 400,000 ha exceeded the total hectarage of all paddy fields. In the in 15 years after the launch and 500,000 ha in 20 years. subsequent 3 years, however, the total application area The progress was steady, but not rapid (Fig. 6). Of the decreased by more than 20%. After maintaining the total application area in 2014, when sorting it out based total application area nearly equal to the total hectarage on the type of herbicides, Jumbo accounted only for of all paddy fields for a few years, it has gradually 4% and 2% in early-season herbicides and middle-to- exceeded the total paddy fields area from 2001. This late-season herbicides, respectively. However, in the © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 85

Fig. 6. Change in the total application area by formulation type. [Color figure can be viewed at wileyonlinelibrary.com] category of one-shot herbicides, Jumbo accounts for 24%, which is the second highest after 1kg-GR of 43%. Fig. 7. The type of Jumbo. [Color figure can be viewed Flowables come third (22%). Regionally speaking, at wileyonlinelibrary.com] approximately half of the paddy fields in Tokai, Kinki and Shikoku are treated with Jumbo. In Hokuriku, of dispersion, herbicides can be submerged after being Chugoku and Kyushu, the number falls to nearly 30%. dispersed and come up onto the surface to float or keep The national average is approximately 30% (Hamamura floating without such initial submergence (Takahashi 2015b). et al. 1996). At this point, all the registered massive types of Jumbo are subjected to submergence, whereas a choice of dispersion process can be made for the Characteristics packed types of Jumbo. As in the other types of formulations for paddy rice, Jumbo can be applied as any Among many advantageous characteristics of Jumbo, soil-applied herbicides, one-shot herbicides, foliar- and especially beneficial are as follows: (i) no need to use soil-applied herbicides or foliar-applied herbicides. sprayers – Jumbo can be easily thrown by hand (with gloves on) from paddy levees, requiring no extra time Usage other than walking along the levees, and lack of a need for knapsack power sprayer use means no time needed During treatment with Jumbo, the depth of flooded to check the engine and adjust the degree of shutter water should be set at 5–6 cm. Care should be given to opening, which is favorable as well; (ii) no need to make sure that the paddies are sufficiently covered with worry about wind drift spreading herbicides to the water without any exposed footprints. Otherwise, neighboring crops; (iii) applicability whenever needed, Jumbo left on the ground might cause not only dis- despite climatic conditions, as application can be carried turbed dispersion but also phytotoxic damage due to out with some contrivance to keep Jumbo dry when locally elevated concentrations of active ingredients. drizzling, and no problems are caused by windiness; Despite the various features included to realize high (iv) easy to work out how many pouches of Jumbo are levels of dispersion, Jumbo has not yet overcome the needed according to the size of a paddy field, enabling physical disturbance of dispersion. Insufficient dispersion the appropriate amount of herbicide to be applied even might occur in the case of peeled surface soil or infesta- in irregularly shaped paddy fields; and (v) low distribu- tion of free-floating algae (e.g., Euglenophyceae), other tion costs such as transportation and storage because a types of algae (e.g., Spirogyra arcla Kutz. and Hydrodict- product package of Jumbo containing herbicides yon reticulatum Lagerth.) and free-floating weeds required for the standard unit of area is smaller than that (e.g., Spirodela polyrhiza (L.) Schleid.). Trapped in of the conventional 3 kg-GR. (In Jumbo, each pouch infested areas, Jumbo cannot disperse properly, resulting weighs approximately 50 g, and 10 pouches are gener- in poor control of weeds in the entire field as well as ally necessary for a paddy field of 0.1 ha) posing a risk of phytotoxic damage to paddy rice in the (Yoshizawa 1995). proximity of the trapped herbicide. For any species of Jumbo is mainly available as either a solid massive algae, if the infestation area is limited to 20–30% of the type or a packed type in which special GRs are total water surface (either distributed across the field or wrapped in a water-soluble film (Fig. 7). In the process cornered by wind), application in the unaffected area © 2018 Weed Science Society of Japan 86 K. Hamamura can produce sufficient levels of dispersion. Regardless of the degree of infestation, it is most effective to apply before or at the incipient stage of algae infestation, that is, as soon as possible after transplantation. After wheat harvest, as scattered straw remains can impede dispersion, the field should be carefully tilled or plowed to ensure no straw remains afloat on the water surface (JAPR 1995; Hamamura 2015b). In the case of a paddy field of 0.3 ha (30 m x 100 m) or smaller, Jumbo should be dispersed evenly while walking around the field, and this should take only 5 min or so. If the shorter side of a paddy field exceeds 30 m, the farmer should walk across the middle of the paddy and throw Jumbo to both the right and left side “ ” of him/herself. When applying during drizzle, some Fig. 8. Size of diffusion granule Mametsubu in com- fi measures should be taken to keep either type of Jumbo parison with 1-kg and 3-kg granules. [Color gure can be dry. Touching with wet hands will induce the disinte- viewed at wileyonlinelibrary.com] gration of massive type, whereas for the packed type, the water-soluble film will be broken, causing the as 1kg-GR, Flowables and Jumbo had already been enclosed GRs to spill out. Jumbo is usable even on used widely. Furthermore, the use of these products windy days. Although wind might cause the floating was promoted exclusively by Kumiai Chemical. The herbicides to fly in the same direction, it will likely ade- total application area of diffusion GRs has therefore quately agitate the water surface, which tends to work increased only slightly and accounts for just 2% of all ’ favorably in terms of dispersion of active ingredients. paddy rice herbicides according to the JAPR s survey However, it is advisable to remember that application is on shipments at the end of September 2014 (Fig. 6). At not recommended if the wind is too strong (JAPR the end of June 2015, a total of 13 Mametsubu formula- 1995, Hamamura 2015b). tions were commercially available, including various types of herbicides such as early-season applications, Diffusion GRs: “Mametsubu” one-shot herbicides and middle- to late-season applications (Hamamura 2015c). Development of “Mametsubu” and its use in cropping practices Characteristics and usage “Mametsubu” is a type of labor-saving formulation pro- prietarily developed by Kumiai Chemical Co., LTD The granular size of Mametsubu formulations ranges (Kumiai Chem.). The research started in 1995, which is from 3 to 8 mm, just like grains of red beans (Kumiai the year following that of the first Jumbo herbicide reg- Chem. 2014). The size of Mametsubu GRs is large, istration. It consists of GRs each the size of red beans especially when comparing it with that of 1 kg-GR and is therefore called Mametsubu (literally translated as (approximately 1 mm) (Fig. 8). As with Jumbo, Mamet- grains of beans). In 2000, the first Mametsubu herbicide subu floats on the water surface after being dispersed (i.e., 250g granules of azimsulfuron + oxaziclomefone and gradually breaks down into very small particles. + pyriminobac-methyl + bensulfuron-methyl) was reg- The particles will then spread over the water surface, istered (Kumiai Chem. 2014). This type of formulation releasing active ingredients to disperse throughout the is categorized as a diffusion GR in the assessment of paddy field. Therefore, Mametsubu can be characterized efficacy and phytotoxicity and is subject to a variety of by the same postapplication floating dispersion as tests, such as applicability tests (carried out by public Jumbo. Some formulations of Mametsubu are wrapped research organizations), small-scale tests on basic disper- with a water-soluble film and are sold as Jumbo sion properties and medium-scale field trials to show (Hamamura 2015c). sufficient levels of dispersion and practicability. Twenty The application instructions for Mametsubu (e.g., the types of Mametsubu formulations have been registered as depth of flooded water and algae infestation at the time paddy herbicides, in addition to other types of pesti- of application and postapplication water management) cides, including fungicides, insecticides and insecticide– are the same as Jumbo. In addition to manual scattering fungicide combinations. When Mametsubu was intro- similar to feeding koi (carp, freshwater fish) in a pond, duced, other preceding labor-saving formulations such Mametsubu can also be applied by throwing the © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 87 herbicide packet with an opening in it or scooping the research enabled the dosage per standard unit of area to contents out with a special ladle and scattering it over be reduced to 500 mL, and improvements on herbicide the paddy field. As with Jumbo, it is thus very easy to preparation and so on were made to extend the scale of apply. Use of knapsack power sprayers or radio- an applicable paddy field to 30 m (JAPR 1995). More- controlled helicopters is also possible. over, “at-irrigation inlet application” was introduced as However, a recommendation is made to consult the a further labor-saving technique, which is applicable to labels of individual products for the suitability of appli- paddy fields meeting certain conditions such as the inlet cation by radio-controlled helicopter. According to water flow rate. Kumiai Chemical, application testing by radio- The total application area of Flowables steadily controlled boat is under way, and the results have been increased as more and more herbicides were registered. favorable so far. When using machines, the application According to the JAPR’s survey on shipments, the total rate should be carefully determined. For example, as application area reached nearly 500,000 ha in 1995 only 250 g of herbicide is required for a paddy field of (Fig. 6). Since then, it has remained more or less the same. 0.1 ha, continuous application at the fully opened shut- As of June 2015, the most common types of Flowable ter setting by a knapsack power sprayer (as in the case herbicides were one-shot herbicides (90 formulations), of 1 kg granule) will cause an herbicide shortage before followed by early-season herbicides (20 formulations). At completion of the entire field. Therefore, for treatment present, no middle-season herbicides are available. with Mametsubu, it is required to adjust the lever to a Regionally speaking, 90% of the rice cropping fields in setting of approximately 25 g per discharge and apply Hokkaido are treated with Flowables, followed by 51% in intermittently while lifting the lever up and down reg- Kanto and 35% in Tohoku. The areas where this is least ularly to repeat the opening/closing of the shutter. This practiced are Tokai (12%), followed by Shikoku (17%) application method is especially recommended for a and Kyushu (18%) (Hamamura 2015d). large paddy field of more than 1 ha. When using radio- controlled helicopters or boats, the herbicide should be Characteristics applied in accordance with the instructed method (Kumiai Chem. 2014). Detailed instructions are given Flowables is a liquid formulation in which active ingre- in the technical documents by the proprietary compa- dients are suspended in water. The product can be nies or sales agencies. directly applied to paddy fields without dilution. Because of this, formulations are prepared in such a Flowables (or suspension concentrate) way that the herbicides sprinkled on rice leaves and stalks can quickly run down. Flowables also have an Development of Flowables and their use in cropping excellent dispersion property in water. Upon applica- practices tion in a paddy field with a width of 30 m, splashing The testing on Flowables for pesticide registration the herbicide from both sides of the paddy field (i.e., 30 started in 1986. The first Flowable formulation for her- m apart from each other) enables the active ingredient bicide was registered in 1990. It was a premix herbicide to disperse and reach the middle of the field. of pyributicarb, benzofenap and bromobutide Flowable. Therefore, uniform application as in the case of GRs The initial dosage was 1 L per standard unit of area is unnecessary, allowing all registered herbicides to be (0.1 ha). Unlike the current common practice of manu- sprinkled manually from levees. Some herbicides can be ally sprinkling over a paddy field from levees, the scattered by radio-controlled helicopters or are suitable farmer had to walk around inside a paddy field to man- for at-transplanting or at-irrigation inlet applications. In ually scatter the herbicide throughout the field. Still, a Hokkaido, as the size of each paddy field is large, radio- substantial labor-saving effect was expected relative to controlled boats are commonly used for application the uniform application of GRs. After the rapid and (Kusume 2015). Flowables are advantageously charac- superior dispersion property of Flowables in water was terized by the lack of necessity of uniform application indicated by numerous tests, a tentative suggestion was across a paddy field, causing no risk of excessive treat- made, as an efficient application method, to shake the ment with herbicides in irregular paddies. Each com- bottle and sprinkle the contents over a paddy field pany has featured bottle designs to provide a good grip while walking along a levee. The field trials confirmed for manual application to a paddy field from the levee that this application method was effective for a paddy (Fig. 9). To achieve prompt dispersion of active ingre- field of up to 20 m in length on the shorter side. In dients after application, the preparation method for 1990, the product was thus promoted with the new each herbicide is unique, and the color and viscosity of method of manual application from levees. Further herbicides widely vary from product to product. As the © 2018 Weed Science Society of Japan 88 K. Hamamura

Fig. 9. Bottle design of the Flowable. [Color ﬁgure can be viewed at wileyonlinelibrary.com] Fig. 11. At-irrigation inlet application. [Color ﬁgure can be viewed at wileyonlinelibrary.com]

herbicide adhering to rice plants. As each bottle has openings that suit a given Flowable product, replacing it with a commercially available pressurized sprayer might cause serious phytotoxic damage (Hamamura 2015d). When applying Flowables, it is desirable to keep the depth of flooded water at approximately 5 cm to achieve a sufficient level of dispersion after application. If the size of a paddy field is 0.3 ha (W 30 m × L 100 m) or smaller, the herbicide can be scattered from a levee while walking along the perimeter of the field. In such cases, the herbicide should be scattered every 3–4 m, and 25–30 applications can empty a single 500 mL bottle. The herbicide user should be careful not to be showered with Fig. 10. Size and number of holes at the inner lid of the contents, keeping the bottle below the waist at the fi the Flowable bottles. [Color gure can be viewed at time of application. On windy days, the herbicide user wileyonlinelibrary.com] should make sure that the content is scattered downwind while walking along the windward side of a paddy field viscosity affects the quantity of discharge and reachable or wading across the field parallel to it (JAPR 1995). distance when scattering, each bottle is equipped with When the water surface is covered with algae, impeded the suitable size and number of holes at the inner lid dispersion of active ingredients might cause variable effi- (Fig. 10). When WDGs are applied using a special con- cacy or locally observed phytotoxic damage. It is there- tainer after dilution in a prescribed amount of water, fore advisable to wade around a paddy field for the the method is, in principle, the same as Flowables uniform application of herbicide throughout the field. If (Hamamura 2015d). the width of a paddy field exceeds 30 m, it is recommended that the herbicide user him/herself walk across Usage in the middle of the paddy field to scatter the herbicide toward both the right and left sides. For even wider It is important to shake the bottle immediately before paddy fields, the number of lines to wade across should use to homogenize the content. However, care is be determined based on the fact that Flowables can dis- needed because shaking too vigorously up and down perse in a distance of up to 15 m (Hamamura 2015d). results in foaming, which consequently causes a variable quantity of discharge. Flowables were prepared to achieve a sufficient level of dispersion through direct At-irrigation inlet application application while avoiding adhesion of herbicide to rice plants. Diluted application might result in poor efficacy The “at-irrigation inlet application” is a method in or severe phytotoxic damage to rice owing to the which the total quantity of herbicide for a given field is © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 89

600

1949(Hand weeding) 500

400

1955 300 1960

200 1965 Weeding hours ( man-hrs / ha )

1970

100 1980 1975 1985 1990 1995 Fig. 12. Change in weeding hours 2000 2005 2010 and the times of herbicide 0 2015 applications. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 collectively poured in at the water inlet when irrigating amount of herbicide should be allocated to each inlet. the field (Fig. 11). Although the time required for After application, the irrigating water should be allowed application is extremely short and is therefore labor sav- to flow out until the desired depth of flooded water is ing, the applicability depends on the flow rate of irri- achieved, at which point the inlet should be closed gating water. In principle, it has to be high enough to promptly and securely. Otherwise, the delayed timing flood a single paddy field to a water depth of approxi- of closing the inlet can let water overflow from the mately 5 cm in 5–6 h. A larger paddy field might have outlet. It is also advisable to fill crayfish holes and so several water inlets; for that reason, this method can be on, if there are any, on the levees beforehand used if the aforementioned condition is satisfied. The (Hamamura 2015d). smaller flow rate causes insufficient dispersion of active ingredients in a paddy field, which might result in vari- Total application area by formulation types able efficacy or even serious phytotoxic damage in herbicide-stagnant areas. For this type of application, In Japan, the first formulation of 2,4-D was the irrigation can be carried out by either of the two fol- WP. However, after that, 3 kg-GR became the most lowing ways: (i) supply water to the puddled field (with common formulation type. In 1985, 3 kgGR a water depth of 0–1 cm) until the flooded water depth accounted for approximately 86% of the total applica- reaches 3–5 cm or (ii) supply water to the flooded field tion area of all formulation types. In the following (with a water depth of approximately 2 cm) until the years, new types of formulations were developed flooded water depth reaches 5 cm or thereabouts. In (e.g., Flowables in 1990 and 1 kg-GR and Jumbo in both cases, all the prescribed amount of herbicide is 1994). Use of these new types of formulations spread poured into the flowing water from the inlet in one rapidly. Within a few years, the order of the total appli- go. With multiple water inlets, an appropriately divided cation area among formulation types was rearranged © 2018 Weed Science Society of Japan 90 K. Hamamura from the highest as follows: 1 kg-GR, Flowables, 3 kg- hours in 2010 and 15 (3%) hours in 2015 (Fig. 12) GR and Jumbo. Of the total application area (JAPR 2014). (2,966,400 ha) in 2015, the proportion of 1 kg-GR, Flowables, Jumbo, 3 kg-GR and diffusion GR was 42, 18, 15, 8 and 2%, respectively. In addition to the CONCLUSION considerable labor-saving effect by the reduced weight In addition to their high level of safety, recently devel- of commonly used granules from 3 to 1 kg, the new oped paddy herbicides with low levels of active ingredi- types of labor-saving formulations, such as Flowables ents can exhibit excellent efficacy against a variety of and Jumbo, expanded their shares in the market (Fig. 6; weed species. With the introduction of various types of Hamamura 2015b). formulations with high labor-saving levels, including one-shot herbicides, the established weed control system has significantly reduced weeding hours. However, there are still many issues to be addressed, including REDUCTION OF WEEDING HOURS DUE herbicide-resistant weeds, difficult-to-control weeds TO DEVELOPMENT OF HERBICIDES such as Sagittaria trifolia L., Eleocharis kuroguwai Ohwi In 1949, before the introduction of herbicides, the main and Scirpus maritimus L., change in the prevalent weed means of weeding was by hand (hand weeding), and species owing to global warming, prolonged weed con- the time required for weeding was 506 h per ha trol periods due to the introduction of direct seeded (regarded as 100%). In 1950, a synthesized auxin, rice cultivation and weedy rice. When supporting agro- 2,4-D, was registered, and with increasing use of herbi- chemical companies for their continuing studies into fi cides, the time required for weeding decreased substan- the development of herbicides with improved ef cacy, tially and fell to 311 h in 1954 (61%) and 268 h in we look to research organizations for the establishment fi 1960 (50%). In 1965, PCP-Ca, which is effective of more ef cient weed control systems that fully utilize against Echinochloa spp., was developed and became herbicides and cropping technologies. commonly used. The weeding hours were lowered to 174 (34%). In 1970, it became as low as 130 h (26%), resulting from the widespread use of soil-applied herbi- ACKNOWLEDGEMENTS cides after the registration of chlornitrofen (CNP) GRs. The author thank all the agrochemical companies that Besides soil-applied herbicides, foliar and soil-applied provided the herbicide shipment data, particularly herbicides were developed, and in 1975, sequential Kumiai Chemical Industry Co., LTD that provided applications of herbicides were established, thus reduc- materials related to the “Mametsubu” formulation, and ing weeding hours to 90 (18%). Sequential applications Mr. Takafumi Takeshita (Technical Adviser, JAPR) were practiced most commonly until the launch of who provided the valuable summary data. The author one-shot herbicides, and in 1980, the weeding hours also thank Dr. Hirohiko Morita (Technical Adviser, decreased to 59 (12%). When one-shot herbicides were JAPR) for his great encouragement during the course released in 1985, the time required for weeding was of writing this paper. reduced to 43 h (8%), successfully cutting it to less than 10% of the hours required before herbicides. In 1990, when ALS inhibitors were introduced to one-shot her- DISCLOSURE STATEMENT bicides, the weeding hours declined to 24 (5%). The required hours became 20 (4%) in 1995, when 1 kg- The author declares no conflict of interest. GR and Flowables were released commercially. Further addition of new labor-saving formulations, such as REFERENCES Jumbo and diffusion GR, enabled the weeding hours to be as low as 18 (3%) in 2000 (Takeshita 2004). In Food and Agricultural Materials Inspection Center (FAMIC). 2017. the following years, against a backdrop of increasing Registered Pesticide Information service. Accessed 21 June 2018. SU-R lowland–weed biotypes across the country, one- Available from URL: http://www.acis.famic.go.jp/searchF/ vtllm000.html shot herbicides especially effective against these weeds Hamamura K. 2011. Trends in herbicide development for rice in paddy or those with a long-residual activity were made avail- fields. J. Weed Sci. Technol. 56, 39 (in Japanese). able. Such one-shot herbicides with distinctive charac- Hamamura K. 2015a. Development of one-shot herbicides for paddy teristics were developed one after another. The time rice. J. Agric. Ext. 52,57–60 Tokyo, (in Japanese). Hamamura K. 2015b. Features and usage of jumbo formulations. J. Agric. required for weeding gradually declined to 14 (3%) Ext. 52,60–62 Tokyo, (in Japanese). © 2018 Weed Science Society of Japan Development of paddy herbicides in Japan 91

Hamamura K. 2015c. Features and usage of Mametsubu formulation. Kusume S. 2015. Spraying technology of Flowable formulation using a J. Agric. Ext. 52,62–63 Tokyo, (in Japanese). radio-controlled boat in paddy field. J. Agricu. Ext. 52, 72 Tokyo Hamamura K. 2015d. Features and usage of Flowable formulations. (in Japanese). J. Agric. Ext. 52,64–66 Tokyo, (in Japanese). Masunaga S. 2000. The origin of and change in, dioxin pollution in Hamamura K. 2015e. Technology for ‘at-transplanting application’ and Japan -the contribution of dioxins in herbicides. Japan Society Mater. ‘at-direct-seedling application’ in rice production. J. Agric. Ext. 52, Cycles Waste Manag. 11, 173–181 (in Japanese with English summary). 67–69 Tokyo, (in Japanese). Ministry of Agriculture, Forestry and Fisheries (MAFF) Minister’sOffice. Herbicide Resistance Action Committee (HRAC) 2017. Available from 2016. Statistics of Agriculture, Forestry and Fisheries, Tokyo (in Japanese). URL: http://hracglobal.com/tools/classification-lookup Statistics Bureau, Ministry of Internal Affairs and Communications Japan Association for Advancement of Phyto-Regulators (JAPR) 1984. (STAT). 2016. Available from: URL: http://www.stat.go.jp/english/ The 20 Year History of JAPR, Tokyo (in Japanese). data/handbook/pdf/2016all.pdf. Accessed 21 June 2018. Statistical Japan Association for Advancement of Phyto-Regulators (JAPR) 1995. Handbook of Japan, Tokyo. The 30 Year History of JAPR, Tokyo (in Japanese). Takahashi H., Takeshita T. and Noritake K. 1996. Development of New Japan Association for Advancement of Phyto-Regulators (JAPR) 2004. Formulation of Herbicide for Paddy Fields With Special Reference to Throw-in The 40 Year History of JAPR, Tokyo (in Japanese). Type Herbicides. In: The First Northeast Asian Area Weed Science Japan Association for Advancement of Phyto-Regulators (JAPR). 2014. Symposium of China, Japan and Korea, Northeast Agricultural The 50 Year History of JAPR, Tokyo (in Japanese). University, Harbin 206–210. Koura S., Ogasawara C., Ueda S., Kondo H., Taniguchi E., Kamoi M. Takeshita T. 2004. Transition of herbicides use in Japan, 1. Paddy et al. 1994a. Diffusion form of Quinoclamine (ACN) giant foaming herbicides. J. Weed Sci. Technol. 49, 220–230. tablet in paddy field water. J. Weed Sci. Technol. 39,91–95 (in Japanese Takeshita T. and Noritake K. 2001. Development and promotion of with English summary). laborsaving application technology for paddy herbicides in Japan. Weed Koura S., Ogasawara C., Ueda S., Takahashi Y., Seki Y., Kamoi M. et al. Biol. Manag. 1,61–70. 1994b. Effect of Quinoclamine (ACN) giant foaming tablets on the Watanabe H. 2011. Development of lowland weed management and control of surface soil separation and green algae. J. Weed Sci. Technol. weed succession in Japan. Weed Biol. Manag. 11, 175–189. 39,96–101 (in Japanese with English summary). Yabuno T., H. Yamaguchi 2001. The Echinochlor spp., Tokyo Kumiai Chemical Industry Co., LTD 2014. Revolution of Labor-Saving (in Japanese). Formulation Zenkoku Noson Kyoiku Kyokai Co., Ltd., Tokyo Yoshizawa N 1995. The recollection of herbicides development, Tokyo (in Japanese). (in Japanese).

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