Weeds that can do both tricks: vegetative versus generative regeneration of the short-lived root-sprouting herbs Rorippa palustris and Barbarea vulgaris

Weeds of arable land have two strategies for coping with severe disturbance: they have either a very short life cycle and survive disturbance events (ploughing) as seeds or they rely on an underground bud bank and a large regeneration capacity from fragmented roots or stems. Representatives of the respective strategies differ in their investments: annual weeds invest in generative structures and production of easily dispersible or durable seeds, whereas perennial weeds invest preferentially to underground storage organs bearing buds which serve for vegetative propagation. Even when perennial weeds may also produce seeds under favourable conditions, these may serve for further field infestation and spreading. However, the ability of some short‐lived annual weeds to regenerate from roots is often overlooked in studies on mechanisms for disturbance survival. Here, we show that short‐lived weeds capable of adventitious sprouting from roots may be very successful in vegetative regeneration from root fragments. Using a pot experiment, short‐lived root sprouters were found to have higher (Rorippa palustris) or the same (Barbarea vulgaris) fitness when regenerating from root fragments as when regenerating from seed. Even though this finding needs to be tested on other species and in different experimental settings, the results indicate the potential importance of adventitious sprouting from roots in short‐lived plants. Better knowledge of this phenomenon is crucial for understanding both the population dynamics of short‐lived root‐sprouters in disturbed habitats and the ruderal strategy of plants generally.     

Impact of crop management on weed species diversity and community composition of winter wheat fields in Iran

The aim of this study was to assess the effects of crop management practices on the diversity, structure, and composition of weed communities. A total of 30 fields (15 fields each) in low‐input and conventional farming systems were surveyed in north‐eastern Iran. In the conventional cropping system, both mineral fertilizers and herbicides were applied, while in the low‐input cropping system, the fertilizer was mainly manure and herbicides were avoided. The results showed that the pool of species, species richness, number of unique species, and Shannon's diversity index were greater in the low‐input system than in the conventional system. Both cropping systems had more broad‐leaved species than grasses and more annual species than perennial species. All the multivariate methods of analysis that were applied revealed that the weed community composition was significantly different between the two management types. The low‐input cropping favored herbicide‐susceptible broad‐leaved weeds, legumes, and weeds with biodiversity value, whereas a high proportion of herbicide‐tolerant grasses was found in the conventional fields. The results suggest that low‐input cropping can sustain high weed diversity and abundance.     

Development of herbicides for paddy rice in Japan

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

Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens

Brandsæter LO, Fogelfors H, Fykse H, Graglia E, Jensen RK, Melander B, Salonen J & Vanhala P (2010). Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens. Weed Research 50 , 102–109.

Summary

The success of weed management aimed at depleting the regenerative structures of perennial weeds depends largely on the sprouting activity of rhizome and root buds. Seasonal variation in sprouting of these buds on Cirsium arvense, Sonchus arvensis and Elymus repens was studied for plants collected from Denmark, Finland, Norway and Sweden. At 2‐week intervals from July to October, 5‐cm fragments of roots or rhizomes were cut from plants grown in buckets and planted into soil in pots, half of which were placed immediately into growth chambers at 18°C for 4 weeks. The other half of the pots were initially placed in a dark room at 2°C for 4 weeks before being transferred to the same growth chamber, also for 4 weeks. During the growth chamber period, the numbers of emerged shoots in each pot were counted weekly. The sprouting activity of C. arvense and E. repens was relatively uniform during this period and bud dormancy was not apparent. In all ecotypes of S. arvensis, innate bud dormancy developed during the latter part of the growing season. For all three species, differences in sprouting readiness were found among ecotypes. The results imply that C. arvense and E. repens are more likely to be controlled by mechanical measures in autumn than S. arvensis.     

The implications of spatially variable pre‐emergence herbicide efficacy for weed management

BACKGROUND

The efficacy of pre‐emergence herbicides within fields is spatially variable as a consequence of soil heterogeneity. We quantified the effect of soil organic matter on the efficacy of two pre‐emergence herbicides, flufenacet and pendimethalin, against Alopecurus myosuroides and investigated the implications of variation in organic matter for weed management using a crop–weed competition model.

RESULTS

Soil organic matter played a critical role in determining the level of control achieved. The high organic matter soil had more surviving weeds with higher biomass than the low organic matter soil. In the absence of competition, surviving plants recovered to produce the same amount of seed as if no herbicide had been applied. The competition model predicted that weeds surviving pre‐emergence herbicides could compensate for sublethal effects even when competing with the crop. The ED50 (median effective dose) was higher for weed seed production than seedling mortality or biomass. This difference was greatest on high organic matter soil.

CONCLUSION

These results show that the application rate of herbicides should be adjusted to account for within‐field variation in soil organic matter. The results from the modelling emphasised the importance of crop competition in limiting the capacity of weeds surviving pre‐emergence herbicides to compensate and replenish the seedbank. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Weed Control in Wheat and Barley in the Middle East

Abstract

Wheat and barley constitute the bulk of agricultural production in the Middle East. Unfortunately, these crops are grown on marginal soils which are infested with annual and perennial weeds. The principal weed species include Avena sterilis L., Convolvulus arvensis L., and Sinapis arvensis L. and it has been estimated that yield losses due to weeds are between 20 and 30%. Control is mostly by hand pulling, hoeing or mechanical tillage, the use of herbicides being limited to about 2–5%, of the cereal area. The chemical used is usually 2,4-D but there are a few applications of barban. With the increase in wages, and unavailability of agricultural labour it is suggested that herbicide application should be widely used in the Middle East. Mixtures with benzonitriles and dicamba should be used in addition to the economical phenoxy herbicides to widen the spectrum of control of broadleaved weeds. Glyphosate may also be used after grain harvest for the control of perennial weeds and tri-allate, chlortoluron and other chemicals for the control of wild oats and other grasses. Plant breeders should study the genetic response of newly developed varieties to the most widely used herbicides.     

Perspective: root exudation of herbicides as a novel mode of herbicide resistance in weeds

The evolution of resistance to herbicides in weeds has become a great challenge for global agricultural production. Weeds have evolved resistance to herbicides through many different physiological mechanisms. Some weed species are known to secrete herbicide molecules from roots into the rhizosphere upon being treated. However, root exudation of herbicides as a mechanism of resistance has only recently been identified in two weed species. Root exudation pathways have been investigated in Arabidopsis, and this work suggested that ATP‐binding cassette (ABC) and multidrug and toxic compound extrusion (MATE) transporters play a role in the secretion of primary and secondary plant products from roots. We hypothesize that the mechanisms involved in root exudation of herbicides that result in resistance are mediated by overactive or overexpressed transporters, probably similar to those found for the exudation of primary and secondary compounds from roots. Elucidating the molecular and physiological basis of root exudation in herbicide‐resistant weeds would improve our understanding of the pathways involved in herbicide root secretion mediated by transporters in plants. © 2020 Society of Chemical Industry     

Weed management in conservation crop production systems

Information on weed management in conservation crop production systems is needed as adoption of practices such as reduced tillage and cover crops becomes more widespread. This review summarizes recent research on weed management aspects in these systems. Changes in patterns of tillage, planting systems, and other management strategies can alter the soil environment and lead to shifts in weed populations. Weed patterns and populations are not always consistent and vary with locale, crop, and herbicide use. However, in many long-term conservation management studies, a general increase in perennial weeds and grass species has been observed. The development of low-dose herbicides, selective postemergence herbicides, and transgenic crops has greatly improved the flexibility of producers who use conservation systems where opportunities for tillage are limited. With a higher level of management inputs, producers can successfully implement conservation management practices.     

湖南省棉田杂草调查

对湖南省棉花主产区棉田杂草的种类、发生规律及化学除草情况进行了调查。结果发现, 湖南省棉田常见杂草包括12科, 28种, 其中禾本科杂草占25.00%, 阔叶杂草占67.86%, 莎草科占7.14%; 一年生杂草占78.57%, 多年生杂草占21.43%。相对多度10%以上的杂草有7种, 其中马唐、牛筋草、千金子、铁苋菜、小飞蓬5种杂草为湖南省棉田杂草的优势种, 相对多度分别为37.79%、33.64%、29.15%、26.23%、23.83%。杂草发生呈现3个高峰期, 分别为5月下旬, 6月中下旬, 7月下旬至8月初, 杂草防除主要采用苗前土壤处理和苗后茎叶处理相结合的化学防除方法。     

The impacts of traditional and novel herbicide application methods on target plants,non‐target plants and production in intensive grasslands

Herbicides contribute significantly to agricultural intensification, but some negatively impact non‐target organisms. Much research has focused on reducing herbicide use through technological improvements in application and herbicide selectivity, but impacts on non‐target organisms are less well understood. Using experimental plots in silage systems, we investigated impacts of herbicides (both narrow spectrum targeting broad‐leaved plants and selective and non‐selective broad spectrum) applied using traditional techniques (blanket‐ and manual spot‐spraying) and a novel application technique (automated spot‐spraying) on non‐target plant richness/diversity, target weed presence (Rumex species) and production (DM yield). All herbicides reduced non‐target plant richness/diversity and sometimes target weeds (when applied using traditional methods). Automated spot‐spraying had fewer negative effects on non‐target organisms, but did not reduce target weeds. No differences in production levels among treatments were observed. The automated spot‐spraying technique requires further research and development. Our results indicate that 20–30% weed cover does not significantly alter production and so, as herbicides are expensive, their effects on non‐target organisms and the environment can be more significant than their benefits to production. We advocate more research into the relationships between weed infestation and production in grasslands, so that the propensity to overuse herbicides is reduced.     

SELECTIVE ACTION OF DIPHENAMID AND NAPROPAMIDE IN PEPPER (GAPSICUM ANNUUM L.) AND WEEDS

Summary. A comparison was made between diphenamid and napropamide with regard to phytotoxicity to pepper and weeds under glasshouse and field conditions. Diphenamid was considerably less phytotoxic than napropamide in inhibiting root elongation and shoot growth of pepper seedlings. Plant growth was reduced when the roots were exposed to either one of the herbicides, but growth of the shoot through treated soil was not adversely affected. Since diphenamid was found to be more leachable into soil, it might become more available to the roots and damage the crop plants. Graminaceous weeds were very sensitive to both herbicides, whereas several dicotyledonous weeds were more susceptible to napropamide. Selectivity of both herbicides at a late pre-emergence application to direct-seeded pepper was found satisfactory in two field experiments on different soil types.
Action sélective de la diphénamide et de la napropamide sur le piment et les mauvaises herbes     

Impacts of cropping system and management practices on the assembly of weed communities

Understanding how weed communities assemble as a function of biotic and abiotic filters and transform through time has important implications for the sustainable management of agronomic systems. In a three‐year study, we evaluated weed community responses to lucerne (Medicago sativa, perennial) vs. continuous spring wheat (Triticum aestivum, annual, CSW) and weed management practices where weeds in the CSW system were managed with three contrasting approaches (herbicide, tillage or sheep grazing). Our results indicated no differences in weed diversity between the perennial and annual crops or across the different management practices in CSW. However, there were differences in weed community composition. Lucerne, with the exception of the establishing year, impeded the growth and reproduction of several annual weeds, including Amaranthus retroflexus, Thlaspi arvense, Lamium amplexicaule and Chenopodium album, but favoured perennial broad‐leaved weeds such as Taraxacum officinale and Cirsium arvense. The replacement of herbicide treatments in pre‐plant and post‐harvest in CSW with soil tillage or sheep grazing selected for different weed communities beyond the second year of establishment. The weed species driving the differences in CSW systems were Androsace occidentalis, more common in CSW managed chemically; Asperugo procumbens, more common in CSW managed with tillage; and T. officinale and Lactuca serriola, more common in CSW managed with sheep grazing. Understanding how cropping systems modify weed communities is a necessary step to shift from reactive weed control programmes to predictive management strategies.     

Modelling the sprouting capacity from underground buds of the perennial weed Sonchus arvensis

Sonchus arvensis is a problematic perennial weed species causing problems in many crops. Control measures often rely on soil tillage or mowing; both methods are used to exhaust the root system. This approach fails during periods of restrictions in sprouting capacity or shoot regrowth. The aim of this study was to develop a simulation model for prediction of shoot sprouting capacity in underground buds of S. arvensis. We hypothesised restricted regrowth to be induced as a function of photoperiod and temperature sum and released as a function of cold temperature sum. The model was parameterised and calibrated against observations of shoot regrowth from an experiment on intact roots of S. arvensis. Subsequently, it was validated against observations of regrowth from another experiment on intact roots and sprouting from fragmented roots from a third experiment. Restriction in regrowth was attributed to reduction in the photoperiod, observed when the day length decreased below a threshold of 16.5 h, but also to a daily mean temperature below 16.8°C. Resumed regrowth occurred in late autumn at a daily mean temperature threshold of 4.7°C. The pattern of changes over time in shoot regrowth from an intact root system was well predicted by the model. The temporal change in sprouting capacity from buds on fragmented roots followed the same pattern, but with a quantitative difference between the model prediction and the observed sprouting capacity. We conclude that the model can be used to predict the pattern over time of sprouting capacity in intact roots of S. arvensis.     

A simulation of herbicide use based on weed spatial distribution

Intensive field surveys were conducted to deter mine the spatial distribution of composite broad leaf and grass weed seedlings in seven maize and five soybean fields in eastern Nebraska in 1992. Farmer fields where herbicides were applied in a 38-cm band over 76-cm spaced rows were chosen for this study. Weed populations were measured in the interrow and in the band-treated intrarow. Spatial maps constructed for grass or broadleaf weeds revealed that individual species as well as species assemblages are highly aggregated. On average, 30% of the sample area in the 12 fields surveyed was free of broadleaf weeds and 70% free of grass weeds in the interrow area (no her bicide). Where a pre-emergence herbicide was applied (intrarow), 71% of the sample area was free of broadleaf weeds and 94% free of grass weeds. Increasing the threshold to some value other than zero resulted in a larger field area not requiring a herbicide application. The results of these distribution studies indicate that herbicide use could be substantially reduced if weed dis tribution maps or real-time plant sensing were available to provide information for intermittent herbicide application systems or refinement of economic thresholds.     

Strategic tillage in Australian conservation agricultural systems to address soil constraints: How does it impact weed management?

In the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre-emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.     

Seed germination ecology of creeping mannagrass (Glyceria acutiflora) and response to POST herbicides

Creeping mannagrass is a perennial grass weed widely distributed in China and is becoming increasingly problematic in nurseries and landscapes in some regions. Understanding the germination ecology and response to commonly available POST herbicides of this weed is critical to determining its adaptive capabilities and potential for infestation, and assist in the development of effective control strategies. In the light/dark regime, creeping mannagrass germinated over a wide range of temperatures (15/5 to 30/20°C), with maximum germination at 20/10°C (95%). No seed germinated at 35/25 or 10/0°C. The time required for 50% of maximum germination increased as temperature decreased. Compared with the light/dark conditions, germination was slightly stimulated when seeds were placed in the dark. Creeping mannagrass is moderately tolerant to osmotic and salt stress, which had 53 and 50% germination rates at ?0.6 mPa osmotic potential and 200 mM NaCl concentration, respectively. Seedling emergence of the seeds buried at a depth of 0.5 cm (86%) was higher than those sowing on the soil surface (17%), but declined with burial depth increasing. There were no differences in the emergence rates from a burial depth 0.5–2 cm. Few seeds (4%) could emerge when seeds were sowed at a depth of 8 cm. POST application of haloxyfop‐R‐methyl, quizalofop‐p‐ethyl, sethoxydim, and pinoxaden provides 100% control of creeping mannagrass at the three‐leaf to five‐leaf stages. To achieve 80% control with clodinafop‐propargyl, mesosulfuron‐methyl, and fenoxaprop‐p‐ethyl, herbicides had to be applied at the three‐leaf stage.     

The implication of stubble tillage for weed population dynamics in organic farming

In practical farming, early and shallow stubble tillage is carried out post‐harvest to stimulate germination of freshly ripened crop and weed seeds, to kill the resulting seedlings and hence to reduce the input into the soil seedbank. Additionally, it aims at reducing perennial weeds by mechanical damage. In this paper, field experiments and laboratory studies are presented which show that stubble tillage can reduce perennial weeds. However, it had a variable effect on annual weeds. After 5 years of experimentation, no effect of stubble tillage was seen on the aboveground vegetation. In contrast, the soil seedbank of the control was roughly doubled where the stubble had been left uncultivated until autumn ploughing. These results indicate that practical experience which assumes that stubble tillage reduces annual weed populations may be correct, despite the fact that in other published studies stubble tillage exerted no control on annual weeds or had a variable effect. This will have practical application in organic arable production systems.     

甲嘧磺隆等3种除草剂对云南黄馨、金钟扦插苗成苗及生长的影响

阔叶杂草是苗圃中重要的危害性杂草,然而控制苗圃阔叶杂草的有效化学方法却很少,主要原因是能防除阔叶草的除草剂往往对苗木不安全或缺少对其安全性研究。选择甲嘧磺隆、乙氧氟草醚和扑草净3种杀草谱较广的除草剂,通过2015年田间小区试验,研究不同用量下这3种除草剂对苗圃常见苗木云南黄馨、金钟扦插苗成苗、发芽、生根、株高等因素的影响。结果显示:用药时雨水、土壤湿度可严重影响植物生长状况,雨水多、湿度大,则发根、出叶少;用药时间影响药剂效应,扦插前用药,药剂影响大于扦插后用药,这可能是扦插前、扦插后苗在遇药时的叶芽状态及水分不同所造成的。研究还发现,药剂对苗木成苗无不良影响,7.5 g a.i./hm~275%甲嘧磺隆WDG处理对苗木出叶、株高无影响;而在生根方面,在药后30 d,只有对照的71.1%,用药后100 d,与对照相当,乙氧氟草醚144、288 g a.i./hm~2,扑草净450、900 g a.i./hm~24个处理的结果与甲嘧磺隆7.5 g a.i./hm~2处理相同;对于甲嘧磺隆15 g a.i./hm~2处理,在前期对苗木出叶、生根都有较大影响,3个月后影响逐渐减少甚至消失;甲嘧磺隆22.5 g a.i./hm~2处理对苗木出叶、生根、株高的抑制可持续3个月以上。     

The effectiveness of old and new strategies for the long‐term control of Pteridium aquilinum,an 8‐year test

There is a need for management strategies to control dominant perennial weeds and restore seminatural communities. We compared the effects of five weed control treatments on dense Pteridium aquilinum relative to an untreated experimental control over an 8‐year period with the aim of restoring acid grassland. The weed control treatments tested were as follows: cutting and bruising, both twice and thrice annually, and herbicide treatment (asulam in year 1 followed by annual spot retreatment of all emergent fronds). Pteridium aquilinum performance and plant species composition were monitored. Data were analysed using Bayesian mixed‐effect models and multivariate techniques. Cutting twice and thrice yearly and the asulam treatment all reduced frond density to zero; both bruising treatments were ineffective. The plant communities in the cut and asulam‐treated plots showed differences from the untreated and bruised plots; the asulam‐treated plots contained more ruderal species and the cut plots were more typical of acid grassland. Acid grassland recovery was fastest in the asulam‐treated plots, but the cut plots caught up after approximately 5 years. There were two important conclusions. First, an intractable weed like P. aquilinum can be eradicated and a vegetation more suited for grazing can be achieved by the continuous application of some treatments over many years. Here, success was achieved by cutting twice/thrice annually, or by a single asulam application followed by annual spot spraying of all emergent fronds for 8 years. Second, bruising, a treatment favoured by some conservation organisations, did not work and cannot be recommended. The use of long‐term, continuously applied treatments might be considered for all perennial weeds with large underground root/rhizome systems.     

湖南省烟田杂草种群调查

为了明确湖南省烟田杂草种群与分布,采用对角线五点取样法在全省烟田进行了系统调查。结果表明,烟田杂草共有30科77种,其中禾本科杂草占比14.29%,阔叶杂草占比81.82%,莎草科杂草占比3.89%;一年生杂草占比75.32%,多年生杂草占比24.68%。相对多度大于3%的杂草有铁苋菜、酸模叶蓼、稗、碎米荠、马唐、繁缕、喜旱莲子草、看麦娘、通泉草、鸭跖草、水苦荬等11种,其中铁苋菜、酸模叶蓼、稗为湖南省烟田优势杂草种群,碎米荠、马唐、繁缕、喜旱莲子草、看麦娘、通泉草、鸭跖草、水苦荬为湖南省烟田区域性优势杂草种群。湖南省烟田杂草防除主要采用苗前土壤处理和苗后茎叶处理相结合的化学防除方法,主要使用的化学除草剂是精异丙甲草胺和砜嘧磺隆。本研究结果表明,湖南省烟田杂草存在区域性差异,应因地制宜制定合适的化学防治方案。