Weeds and weed management in rice production in Japan

The area of paddy rice fields in Japan was 1.79 million ha in 1998 almost all of which was planted with young seedlings from nursery boxes by a mechanical rice transplanter. Japanese farmers controlled paddy weeds mainly by chemical herbicides, which were applied around 1.8 times in one growing season of rice by sequential treatment. The cost of herbicides was 35 320 ¥/ha on average, the main of which was ‘one‐shot’ herbicides, while weeding labor for the paddy field, including herbicide application, was 19.0 h/ha, or 29 976 ¥/ha in labor cost, in 1998. Under the Integrated Weed Management (IWM) for sustainable paddy rice production, other technologies for weed management are also recommended to paddy farmers, such as ecological or cultural, mechanical, biological methods and so on.     

Weed problems and their management in rice fields of Malaysia: An overview

The available literature on weed problems and weed control in rice fields in Malaysia is reviewed and suggestions for future research are included. The problem of weed competition with rice is of great economic importance in the country because it causes a 10–35% reduction in grain yield. About US$4.10 million is spent annually on herbicides for rice alone, and this amounts to approximately 7% of the total expenditure on herbicides. The shift in methods of rice culture from transplanting to direct seeding has magnified the weed problem. The problem of weedy rice is particularly acute in the direct-seeding rice areas. Although a number of sulfonylurea herbicides (e.g. cinosulfuron, metsulfuron, bensulfuron and pyrazosulfuron) have been found to be suitable alternatives to the old herbicide 2,4-D, an integrated weed management program must be developed in order to reduce the problem of herbicide resistance in weeds. Weed control methods that are more friendly to the environment and affordable to farmers must be sought. Weed-competitive and allelopathic rice varieties must be produced. The problem of weeds in rice calls for systematic studies on biotechnological methods of control of weedy rice. Detailed studies on the biology and ecology of notorious rice weeds, particularly Oryza sativa L. (weedy rice), Echinochloa spp., Leptochloa chinensis (L.) Nees, Fimbristylis miliacea (L.) Vahl. and Limnocharis flava (L.) Buch. need to be done in order to formulate successful weed control measures.     

Integrated pest management and weed management in the United States and Canada

There is interest in more diverse weed management tactics because of evolved herbicide resistance in important weeds in many US and Canadian crop systems. While herbicide resistance in weeds is not new, the issue has become critical because of the adoption of simple, convenient and inexpensive crop systems based on genetically engineered glyphosate‐tolerant crop cultivars. Importantly, genetic engineering has not been a factor in rice and wheat, two globally important food crops. There are many tactics that help to mitigate herbicide resistance in weeds and should be widely adopted. Evolved herbicide resistance in key weeds has influenced a limited number of growers to include a more diverse suite of tactics to supplement existing herbicidal tactics. Most growers still emphasize herbicides, often to the exclusion of alternative tactics. Application of integrated pest management for weeds is better characterized as integrated weed management, and more typically integrated herbicide management. However, adoption of diverse weed management tactics is limited. Modifying herbicide use will not solve herbicide resistance in weeds, and the relief provided by different herbicide use practices is generally short‐lived at best. More diversity of tactics for weed management must be incorporated in crop systems. © 2014 Society of Chemical Industry     

几种封闭除草剂两个时期用药效果对比及其交互作用分析

通过田间小区试验评价了前期筛选的几种适用“播喷同步”的封闭除草剂对水稻的安全性及对直播田杂草的防效, 明确了“播喷同步”技术与常规播后4 d封闭的差异, 以及施药时期×除草剂种类交互作用及对控草效果的影响, 优化水稻直播田杂草防控策略?试验结果表明, 播种当天(播喷同步)或播种后4 d(常规方法)喷施120 g/L噁草酮EC 360 g/hm2+10%苄嘧磺隆WP 30 g/hm2(有效剂量, 下同)?33%嗪吡嘧磺隆WG 74.25 g/hm2+300 g/L丙草胺EC 450 g/hm2?60%丁草胺EC 1 350 g/hm2+10%吡嘧磺隆WP 30 g/hm2?35%吡嘧·嘧草·丙OD 525 g/hm2?300 g/L丙草胺EC 450 g/hm2+10%苄嘧磺隆WP 30 g/hm2, 5组除草剂处理对直播稻均无可见药害, 各“播喷同步”处理的杂草防除效果不低于常规播后4 d用药; 同步喷施33%嗪吡嘧磺隆WG+300 g/L丙草胺EC防效最高, 药后35 d对禾本科?莎草科?阔叶草防效达到98.3%及以上; 水稻直播4 d后喷药, 水稻成苗率提高但 35 d 的禾本科杂草防效低, 33%嗪吡嘧磺隆WG+300 g/L丙草胺EC处理受喷药时间影响小; 复合双因子方差分析表明, 单一因子会对水稻安全性?杂草防效产生显著影响, 用药时期×除草剂种类交互对水稻安全性无显著影响, 对控草效果影响显著?因此, 直播田封闭除草剂宜尽早施药提高防治效果, 同时应选用安全高效的除草剂, 33%嗪吡嘧磺隆WG+300 g/L丙草胺EC处理, 可于播种当天到播种后4 d内用药, 保障直播田杂草防治效果的同时兼顾水稻安全?     

Herbicide‐resistant weed management: focus on glyphosate

This review focuses on proactive and reactive management of glyphosate‐resistant (GR) weeds. Glyphosate resistance in weeds has evolved under recurrent glyphosate usage, with little or no diversity in weed management practices. The main herbicide strategy for proactively or reactively managing GR weeds is to supplement glyphosate with herbicides of alternative modes of action and with soil‐residual activity. These herbicides can be applied in sequences or mixtures. Proactive or reactive GR weed management can be aided by crop cultivars with alternative single or stacked herbicide‐resistance traits, which will become increasingly available to growers in the future. Many growers with GR weeds continue to use glyphosate because of its economical broad‐spectrum weed control. Government farm policies, pesticide regulatory policies and industry actions should encourage growers to adopt a more proactive approach to GR weed management by providing the best information and training on management practices, information on the benefits of proactive management and voluntary incentives, as appropriate. Results from recent surveys in the United States indicate that such a change in grower attitudes may be occurring because of enhanced awareness of the benefits of proactive management and the relative cost of the reactive management of GR weeds. Copyright © 2011 Society of Chemical Industry     

Prevalence of herbicide‐resistant weed species in Malaysian rice fields: A review

The management of weeds in Malaysian rice fields is very much herbicide‐based. The heavy reliance on herbicide for weed control by many rice‐growers arguably eventually has led to the development and evolution of herbicide‐resistant biotypes in Malaysian rice fields over the years. The continuous use of synthetic auxin (phenoxy group) herbicides and acetohydroxyacid synthase‐inhibiting herbicides to control rice weeds was consequential in leading to the emergence and prevalence of resistant weed biotypes. This review discusses the history and confirmed cases and incidence of herbicide‐resistant weeds in Malaysian rice fields. It also reviews the Clearfield Production System and its impact on the evolution of herbicide resistance among rice weed species and biotypes. This review also emphasizes the strategies and management options for herbicide‐resistant rice field weeds within the framework of herbicide‐based integrated weed management. These include the use of optimum tillage practices, certified clean seeds, increased crop competition through high seeding rates, crop rotation, the application of multiple modes of action of herbicides in annual rotations, tank mixtures and sequential applications to enable a broad spectrum of weed control, increase the selective control of noxious weed species in a field and help to delay the resistance evolution by reducing the selection pressure that is forced on those weed populations by a specific herbicidal mode of action.     

Change in weed control studies of rice paddy fields in Korea

This paper was reviewed on the research status of weed control according to cultivating patterns of rice in Korea. Weed control study in a nursery bed was chiefly carried out to control the species of barnyardgrass at the times of machine transplanting. Propanil and nitrofen were applied successfully in wet-nursery beds, and chlornitrofen and pyrazolate/butachlor were also successfully applied in protected semi-irrigated rice nursery beds in the 1970s. Sequential application of herbicides in the mid-1980s has resulted in the end of hand weeding. In machine transplanting, basic research such as the selection of herbicides was conducted in the early 1970s, and its related research including crop injury, seedling age, and reaction of cultivars were done in the late 1970s to early 1980s. Effects of the continuous application of herbicides and its methods of labor saving for rice cultivation were studied in the mid to late 1980s. When the rice planting methods were newly established, such as transplanting when seedlings were 10-days-old and direct seeding from the early 1990s, weed control research relating to herbicides was carried out (e.g. herbicide registration, crop injury, water management, appropriate application time, and neighboring application with insecticide). Weed control for the dill seeding of fields in wetted and reclaimed saline land have been experimented with, particularly in terms of the physio-ecological characteristics and the control of problematic weeds, and the resistance of weeds to herbicides was also investigated systematically.     

Sulfonylurea resistance in Lindernia micrantha, an annual paddy weed in Japan

Resistance to sulfonylurea herbicides, including bensulfuron-methyl, pyrazosulfuron-ethyl, imazosulfuron and ethoxysulfuron, was discovered in naturally occurring populations of Lindernia micrantha D. Don in rice fields that had been treated with sulfonylurea-based herbicides for 3–7 consecutive years. The resistant biotype was approximately 80≈300 times more resistant than the susceptible one to the above four sulfonylurea herbicides. This is the second confirmed occurrence of herbicide resistance resulting from the use of sulfonylurea herbicides in Japan. Several herbicides with different modes of action, including pretilachlor, cafenstrole, bifenox, naproanilide, thiobencarb + simetryn + MCPB, MCPA-thioethyl + simetryn and cyhalofop-butyl + bentazone, effectively controlled the resistant biotype in pot trials.     

苗期水分管理对水稻分蘖及除草剂控草效应的影响

稻田除草剂大量及高频使用对农作物安全、土壤及水体环境构成了严重威胁,使得除草剂减量使用刻不容缓。水稻机插田药后长时间保水可显著抑制杂草,以此可减少除草剂用量,但长时间保水会导致水稻发育受限。盆栽试验表明,无论是否喷施除草剂30%苄嘧·丙草胺乳油,杂草发生随保水时长增加而减少,且喷施除草剂对杂草防除具显著效果。田间试验表明,稻田施用30%苄嘧·丙草胺乳油100 mL/667m~2后,药后保水7 d时的水稻分蘖及抑草的综合效应达到最佳。     

Our top 10 herbicide‐resistant weed management practices

Although proactive or reactive herbicide‐resistant weed management (HRWM) practices have been recommended to growers in different agroecoregions globally, there is a need to identify and prioritise those having the most impact in mitigating or managing herbicide selection pressure in the northern Great Plains of North America. Our perspective on this issue is based on collaborative research, extension activities and dialogue with growers or farming experience (cereal, oilseed and pulse crop production) during the past 30 years. We list our top 10 HRWM practices, concluding with the number 1 practice which is the foundation of the other nine practices: crop diversity. Although our top 10 HRWM practices have broad applicability across agroecoregions, their ranking may vary widely. © 2017 Society of Chemical Industry     

3种除草剂对水稻旱直播阔叶杂草防效及安全性研究

为明确不同除草剂茎叶处理对旱直播水稻田旱生阔叶杂草防除及安全性的影响,采用随机区组试验设计,选用30% 2,4-滴丁酸钠盐AS、84%氯酯磺草胺WG、480 g/L灭草松AS 3种除草剂在水稻4叶期、5叶期施用,施药后每间隔7 d测定杂草株防效、鲜重防效和水稻目测药害,同步测定水稻生长指标和抗逆酶活性。结果表明:30% 2,4-滴丁酸钠盐AS 900.0 g/hm2在水稻4叶期的杂草防效最佳,第28天杂草株防效及鲜重防效仍可达93.55%和96.42%,且对大龄鸭跖草防效显著,施药后水稻生长与人工除草相比无显著差异。叶片SOD、POD活性和MDA含量均先升后降,至施药后28 d恢复正常。30% 2,4-滴丁酸钠盐AS 900.0 g/hm2可高效防除阔叶杂草,该药剂在水稻4叶期和5叶期施用对旱直播水稻安全。     

我国杂草科学学科发展现状与展望

杂草科学是研究杂草生物学特性、生长发育规律、分类与鉴定、分布与危害、群落结构与演替、抗药性机制、防治技术的综合学科。本文重点阐述了近5年(2018年－2022年)来我国杂草科学学科在杂草生物学与生态学、杂草抗药性机理、除草剂安全剂作用机理、杂草防控技术等领域取得的系列研究进展, 并展望了今后杂草科学学科的发展方向。     

Occurrence of sulfonylurea resistance in Sagittaria trifolia,a basal monocot species,based on target‐site and non‐target‐site resistance

Sagittaria trifolia L. is one of the most serious weeds in paddy fields in Japan. Since the late 1990s, severe infestations of S. trifolia have occurred following applications of sulfonylurea herbicides in Akita prefecture. In this study, two accessions of S. trifolia, R1 and R2, were collected from paddy fields with severe infestations and their resistance profiles were determined in comparison to a susceptible accession, S1. R1 and R2 were highly resistant to bensulfuron‐methyl. R1 was also highly resistant to pyrazosulfuron‐ethyl, but R2 was susceptible. Relative to S1, R1 had an amino acid substitution at the Pro₁₉₇ residue of acetolactate synthase (ALS), a well‐known mutation that confers sulfonylurea resistance, suggesting that R1 has a target‐site‐based resistance (TSR) mechanism. The sequence of the ALS gene in R2 was identical to that in S1. A Southern blot analysis indicated that there was only one copy of the ALS gene in S1 and R2. These results suggest that R2 has a non‐target‐site‐based resistance (NTSR) mechanism. R2 was moderately resistant to imazosulfuron but susceptible to thifensulfuron‐methyl. R2 and S1 were susceptible to pretilachlor, benfuresate, MCPA‐ethyl and bentazon. The results reveal the occurrence of two sulfonylurea‐resistant biotypes of S. trifolia that show different mechanisms of cross‐resistance to sulfonylureas related to TSR in R1 and NTSR in R2.     

Development of chemical weed control and integrated weed management in China

More than 200 species of weeds are infesting main crop fields in China, among which approximately 30 species are major weeds causing great crop yield losses. About 35.8 million hectares of crop fields are heavily infested by weeds and the annual reduction of crop yields is 12.3–16.5% (weighted average). Along with rural economic development, approximately 50% of the main crop fields undergo herbicide application. Chemical weed control has changed cultural practices to save weeding labor in rice, wheat, maize, soybeans and cotton. At the same time, continuous use of the same herbicides has caused weed shift problems and weed resistance to herbicides. Consequently, integrated weed management in main crops is being developed.     

抗药性杂草与治理

抗药性杂草对农田杂草治理和农业生产构成严重威胁,成为备受全球关注的严重问题。随着长期、大量使用相对有限的化学除草剂,全球抗药性杂草发展迅猛,目前已有217种杂草对化学除草剂产生了抗药性,我国抗药性杂草发展也十分迅猛。本文在介绍杂草抗药性基本概念、抗药性杂草发展过程、抗药性杂草现状的基础上,重点描述了抗药性杂草治理策略,以期为我国抗药性杂草研究和治理提供参考。     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

Potential allelopathic rice lines for weed management in Cambodian rice production

In Cambodia, the planting of rice lines with a competitive and/or allelopathic ability would be a very useful way to supplement weed management in the rain‐fed, low‐input production systems. The present study examines a wide range of rice germplasm, mainly from Cambodia, and uses a series of bioassay techniques to identify those that might have a weed growth‐suppressing, allelopathic trait. A laboratory bioassay study that involved 359 rice lines showed that there were 15 that could significantly reduce the growth of awnless barnyard grass seedlings. In a second laboratory bioassay, involving the best 96 rice lines that were identified in the first study, 14 were shown to suppress the shoot growth of awnless barnyard grass, 11 could suppress the shoot growth of barnyard grass, six could suppress the shoot growth of small umbrella sedge, four could suppress the shoot growth of two‐leaf fimbristylis, four could suppress the shoot growth of water primrose, and three could suppress the shoot growth of gooseweed. Of the 13 rice lines that were able to suppress the growth of at least two weed species, there were three lines that could suppress the growth of three weed species, one line that could suppress the growth of four weed species, and one line that could suppress the growth of five weed species. In a third soil‐based, pot bioassay that studied the 18 best lines coming from the second laboratory bioassay, all showed a significant weed growth‐suppressive ability. A linear regression analysis showed that there was no correlation between their weed growth‐suppressive ability and their physical seedling size, supporting the idea that the growth suppression was allelopathic in nature and not a physical competition effect. In summary, the results indicate that an allelopathic trait does exist in some Cambodian rice lines and that this trait is effective in the growth suppression of a number of major rice weeds.     

Herbicidal activity on acetolactate synthase‐resistant barnyardgrass (Echinochloa crus‐galli) in Arkansas,USA

The intensive use of the acetolactate synthase (ALS)‐inhibiting herbicides, imazethapyr, penoxsulam and bispyribac‐sodium, in imidazolinone‐resistant (Clearfield) rice increases the risk of the evolution of ALS‐resistant barnyardgrass. In 2009, imazethapyr failed to control barnyardgrass that was collected from a field in Arkansas, USA, following the failure of the herbicide in 2008. A greenhouse experiment was conducted to confirm and document the level of resistance of the biotype against three ALS‐inhibiting herbicides that currently are labeled in rice. The level of control of the resistant biotype at the labeled rate of bispyribac‐sodium of 35 g ai ha^?1 was 10%, penoxsulam at 22 g ai ha^?1 was 0% and imazethapyr at 70 g ai ha^?1 was 25%. The level of mortality of the susceptible biotype was 100% with all the herbicides at the labeled rate. The dose needed to kill 50% of the resistant plants was 49 g ha^?1 of bispyribac‐sodium, 254 g ha^?1 of penoxsulam and 170 g ha^?1 of imazethapyr. For the susceptible biotype, bispyribac‐sodium at 6 g ha^?1, penoxsulam at 10 g ha^?1 and imazethapyr at 12 g ha^?1 killed 50% of the treated plants. Based on these findings, it was confirmed that a barnyardgrass population has evolved cross‐resistance to three ALS‐inhibiting herbicides in rice culture in Arkansas. Furthermore, an experiment was conducted to determine if the ALS‐resistant biotype could be controlled using other mechanisms of action. The results indicated that propanil, a photosystem II inhibitor, and quinclorac, a synthetic auxin, failed to control the resistant biotype at the labeled rates, whereas all the other evaluated herbicides provided effective control of both biotypes.