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.     

Composition of floating weed seeds in lowland rice fields in China and the effects of irrigation frequency and previous crops

The diversity and composition of floating weed seed communities were surveyed in 27 sites across the main rice-growing regions in China with the aim of better understanding weed seed dispersal via irrigation water. Seed of 74 species, belonging to 20 families, were identified from floating matter on the water surface in lowland rice fields. Thirty-five species from three families: Poaceae (15), Asteraceae (11), and Polygonaceae (9), accounted for 47% of all species identified. Species with seed maturing in the summer accounted for 64% of the weed seed and their mean relative abundance was 0.74. Species richness, Shannon–Wiener index and Pielou evenness index were significantly different among the floating weed seed communities. The diversity of weed seed communities in the Yangtze river valley was higher than that in other sites, and some sites were dominated by only a few weed species, such as Beckmannia syzigachne , Alopecurus aequalis , A. japonicus , and Polypogon fugax. At all sites, the dominant weed seeds reflected the dominant weed species in the previous crop. The 27 sample sites of weed seed communities can be clustered into two groups on the basis of previous crop, either lowland rice or sites with previous crops of winter fallow, winter wheat or oilseed rape. Canonical correspondence analysis (CCA) revealed that irrigation frequency, previous crop, and latitude, but not soil type or longitude, significantly affected species composition. The numbers of floating weed seed species were high in lowland rice fields; composition was affected by previous crops and irrigation frequency. Filtering irrigation water and collecting and removing floating weed seeds from the water surface could be integrated into weed management practices to control weeds in lowland rice fields.     

单季晚稻稻曲病防治适期研究

通过不同时期接菌诱发试验,得出水稻破口前10～20d是稻曲病菌侵入的敏感期;在不同时期用药防治试验中得出水稻破口前8～15d防治效果最好。据此提出单季晚稻稻曲病的防治适期为水稻破口前10d左右进行。     

Concepts in weed control -- how does biocontrol fit in?

Up until now there have only been twoprincipal concepts in weed control: control at any cost, and theuse of economic thresholds. Control at any cost is characteristicof situations where no effective control methods are available.The use of economic thresholds has evolved alongside chemicalcontrol, enabling weeds to be controlled effectively and at areasonable price. A future concept may be that of ecologicalthresholds, which takes into account not only the costs but alsothe benefits of weeds. The role that weed control methods shouldfulfil in arable crops, and how biocontrol methods can meet theserequirements, is discussed     

Germination ecology of Leptochloa chinensis: a new weed in the Italian rice agro-environment

Leptochloa chinensis is a new weed that has been found with increasing frequency in Italian rice paddies. The germination ecology of L. chinensis seeds was studied in order to investigate the development mechanisms and survival strategy of this weed in rice paddies of northern Italy. Leptochloa chinensis seeds showed no dormancy and exhibited germination even in anoxic conditions. Germination was strongly influenced by temperature (minimum around 15°C; optimal 25–35°C) and light (phytochrome dependent). Temperature fluctuation caused an increase of seed germination in the dark. Seed burial also strongly inhibited germination and emergence of this species. At 5 cm seed burial only 5% of seedlings emerged in flooded conditions, while at the same depth, but with no flooding, no seedling emergence was observed. This phenomenon was not due to oxygen depletion, as germination was not inhibited by complete anoxia, as demonstrated by the fact that some seedlings did emerge in flooding conditions when water was no deeper than 6 cm. Seed burial and concomitant flooding induced an unusual germination: first coleoptile emergence and subsequently emergence of the radicle was observed. The possible exploitation of this knowledge for weed management is discussed.     

A review of non-chemical weed control on hard surfaces

Weed control research to date has mainly focused on arable land, especially regarding herbicides, but also regarding non‐chemical methods. Some of these experiences can be applied to hard surface areas. However, weeds on hard surface areas cause problems that are different from those on arable land. Additionally, crop tolerance does not need to be considered when choosing an appropriate weed control method on these areas. The aim of this review is to describe current knowledge of weeds and weed control methods on hard surface areas and reveal potential ways of advancement. One of the shortcomings of non‐chemical weed control on hard surfaces thus far, is a lack of proper definition of efficiency of the weed control methods. To obtain effective control, more frequently repeated treatments are required than chemical weed management, thereby increasing the costs of labour and fuel. One way to reduce costs can be by adjusting the level of control to the required visual street quality. Weeds are adapted to the hard surface environment and may be less susceptible to certain control methods. This review indicates that for efficient weed control on hard surfaces there is a need for combining weed control techniques, applying sensors for detecting weeds, adapting the energy dose to type of weed flora and prevention of weeds by improved construction of new surfaces.     

Reduced rates of residual and post-emergence herbicides for weed control in vineyards

In 1997 and 1998, five field studies were conducted at four Portuguese wine‐growing regions in order to evaluate the effectiveness of the chemical control of vineyard weeds under Mediterranean conditions using either reduced doses of residual herbicides or only foliar herbicides. Amitrole (3440 g a.i. ha^?1), amitrole + glyphosate mono‐ammonium salt (1720 + 900 g a.i. ha^?1), amitrole (3400 g a.i. ha^?1), amitrole + diuron (2580 + 1500 g a.i. ha^?1), amitrole + simazine (2580 + 1500 g a.i. ha^?1), amitrole + terbuthylazine (2580 + 1500 g a.i. ha^?1) and amitrole + diuron + simazine (2580 + 1300 + 1400 g a.i. ha^?1) were assayed and compared with the following reference herbicides: glyphosate isopropylamine salt (1800 g a.i. ha^?1), amitrole + diuron (2520 + 1680 g a.i. ha^?1), diuron + glyphosate + terbuthylazine (1275 + 900 + 1425 g a.i. ha^?1), amitrole + simazine (1900 + 3900 g a.i. ha^?1) and glyphosate + simazine (800 + 2200 g a.i. ha^?1). The herbicides were applied during late winter. The results indicated that good control was achieved by the application of foliar herbicides alone or of reduced rates of a mixture of residual herbicides with foliar herbicides for at least 2 months. Three months after application, the efficacy of post‐emergence herbicides and lower rates of residual herbicides decreased significantly in clay soils and under heavy rainfall conditions. Convolvulus arvensis– a weed that is becoming increasingly significant in Portuguese vineyards – was poorly controlled, even when glyphosate was used. Despite this, it can be assumed that in those regions in which the trials were conducted, it is possible to employ weed control strategies that entail the elimination or a reduction in the rate of residual herbicides.     

Non-chemical weed control on traffic islands: a comparison of the efficacy of five weed control techniques

The efficacy of five non‐chemical weed control methods for reducing weed cover on traffic islands was investigated in the growing season of 2004. Three trial sites were divided into six treatment areas which were treated with either flame, steam, hot air, hot water, brushes or left untreated. The treatments were carried out at regular intervals throughout the growing season. The percentage weed cover was measured every second week using a 75 × 75 cm quadratic frame with 100 squares. In the control areas, a rapid increase in weed cover was observed, whereas all treatments reduced weed cover. Hot water was the most effective method, although not significantly better than hot air or steam. Hot air treatment was more effective than brushing, whereas hot water was more effective than both flaming and brushing. The doses that were used were relatively high (150–355 kg ha^?1), partly because of the irregular shape of the traffic islands and the treatment intervals were quite short in comparison with those in similar studies. However, the treatments could keep down the weeds only to a certain extent. The present knowledge of the efficacy of various weed control methods, as well as an increase in our knowledge of adequate treatment intervals, supports an optimisation of hard‐surface weed control. Data and experience gained from these trials were used to develop further calibrated application studies.     

鄱阳湖区稻田杂草防控技术规程

本文根据江西滨湖地区稻田杂草群落近20年来的演替情况,提出了鄱阳湖稻区不同水稻栽培方式条件下,各类型水稻田间杂草综合配套防控技术。     

Critical periods for weed control in cotton in Turkey

Field studies were conducted over 4 years in south‐eastern Turkey in 1999–2002 to establish the critical period for weed control (CPWC). This is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. A quantitative series of treatments of both increasing duration of weed interference and of the weed‐free period were applied. The beginning and end of CPWC were based on 5% acceptable yield loss levels which were determined by fitting logistic and Gompertz equations to relative yield data representing increasing duration of weed interference and weed‐free period, estimated as growing degree days (GDD). Total weed dry weight increased with increasing time prior to weed removal. Cotton heights were reduced by prolonged delays in weed removal in all treatments in all 4 years. The beginning of CPWC ranged from 100 to 159 GDD, and the end from 1006 to 1174 GDD, depending on the weed species present and their densities. Practical implications of this study are that herbicides (pre‐emergence residual or post‐emergence), or other weed control methods should be used in Turkey to eliminate weeds from 1–2 weeks post‐crop emergence up to 11–12 weeks. Such an approach would keep yield loss levels below 5%.     

油菜茬水稻赤枯病重发原因分析及防治建议

分析海门市油菜后茬水稻田赤枯病严重发生的原因,主要与土壤缺钾、土壤中产生有毒物质和低温阴雨气候等因素有关。在此基础上,提出了合理施肥、加强田间管理和发病后及时补救措施的治理对策。     

Modelling interactions between herbicide dose and multiple weed species interference in crop–weed competition

The effects of a range of herbicide doses on crop–multiple weed competition were investigated. Competitivity of Galium aparine was approximately six times greater than that of Matricaria perforata with no herbicide treatment. Competitivities of both weeds decreased with increasing herbicide dose, being well described by the standard dose–response curve with the competitivity of M. perforata being more sensitive than that of G. aparine to a herbicide mixture, metsulfuron‐methyl and fluroxypyr. A combined model was then developed by incorporating the standard dose–response curve into the multivariate rectangular hyperbola competition model to describe the effects of multiple infestation of G. aparine and M. perforata and the herbicide mixture on crop yield. The model developed in this study was used to predict crop yield and to estimate the herbicide dose required to restrict crop yield loss caused by weeds to an acceptable level. At the acceptable yield loss of 5% and the weed combination of 120 M. perforata plants m^?2 and 20 G. aparine plants m^?2, the model recommends a mixture of 1.2 g a.i. ha^?1 of metsulfuron‐methyl and 120 g a.i. ha^?1 of fluroxypyr.     

Common reed (Phragmites australis) control is influenced by the timing of herbicide application

Herbicides are typically used as the primary method of weed control. Since common reed (Phragmites australis subsp. australis) infestations in terms of density are relatively large in the State of Nebraska, USA, determining the most appropriate timing of herbicide application is critical for developing a weed management programme. Therefore, several field studies were conducted in 2007 and 2008 at three locations along the Platte River, Nebraska, with the aim of assessing the effect of herbicide selection and timing of application on common reed control. Three herbicides (glyphosate, imazapyr, and imazamox) were applied either alone at two doses or as two-way mixtures on three growth stages of common reed, including vegetative, flowering, and seed filling stages. Both doses of imazapyr (280 and 560 g active ingredient [a] ha^?1) provided the highest level of control (≥ 92%) across all three timings, while imazamox provided the lowest level of control. For example, imazamox applied alone at 280 and 560 g a ha^?1 provided poor control (≤ 60%) across all three timings at the highest rating date. Imazapyr and glyphosate provided the highest levels of control (90%) by the end of the first growing season and into the next growing season (390 to 450 days after treatment, DAT), regardless of the herbicide application time. Imazamox and glyphosate provided the lowest level of control (< 30%) at the first application time at 450 DAT, but slightly improved control with later timings (74% and 85% control at the flowering and seed filling stages, respectively). Stem density decreased in all herbicide applications and timings except for imazamox at both doses during the vegetative growth stage, which was not significantly different than the untreated control.     

Evaluation of rice allelopathy in hydroponics

The inhibitory activity of water extracts from the shoots and roots of three rice cultivars, Taichung native 1 (TN1) and IAC165 (both allelopathic rice) and AUS196 (non-allelopathic rice), grown in hydroponics was evaluated. The release of germination inhibitors by allelopathic rice plants into hydroponic solution was also determined with freshly collected solution and XAD-4 resin desorbate. The degree of the inhibition was quantified in terms of root growth in Echinochloa colona, Echinochloa crus-galli, Echinochloa crus-galli var. oryzicola, Triantema portulacastrum and Lactuca sativa. The allelopathic activity of rice was species specific, and depended on source and concentration. Root length of all test species was inhibited by the different concentrations of shoot extract of allelopathic and non-allelopathic rice. However, of the three cultivars, TN1 showed higher inhibition than IAC165 and AUS196 in all test species. Water extracts of shoots and roots significantly inhibited root growth in E. crus-galli but the shoot extract gave a greater inhibitory effect on E. crus-galli than the root extract. Root exudate of TN1 inhibited root elongation of E. crus-galli from 2 weeks after transplanting (WAT) and the inhibition continued for 4 WAT. The results confirmed the previous finding of a laboratory bioassay that the TN1 had allelopathic activity and produced allelochemicals that inhibit growth of some weed species.     

二化螟田间为害株率与为害丛率间的关系

通过不同调查者调查相同稻田内二化螟为害的枯鞘、枯心和白穗等受害稻株,分析平均受害株率和平均受害丛率的关系。结果表明,“平均受害丛率”在不同调查者之间的误差小于“平均受害株率”。受害株率和受害丛率之间呈正相关的关系,当受害丛率小于60%时,受害株率与受害丛率的相关系数超过0.91,用受害丛率可以较准确地估计受害株率。