The role of dimorphic achenes in the biology of the annual weed Leontodon longirrostris

Various aspects of the reproductive biology and dimorphism of achenes from the annual heterocarpic weed Leontodon longirrostris (Finch & PD Sell) Talavera were studied in the laboratory and field. The species is self-incompatible, pollinated by generalist insects and produces two different types of achene in the capitula: peripheral and central achenes. Peripheral achenes are heavier (1.63 mg) and exhibit virtually no pappus and short-range dispersal, whereas central achenes are lighter (0.45 mg), possess a well-developed pappus and are produced in greater numbers. The morphological differences between the two types of achene result in differences not only in dispersal, but also in germination, seedling vigour and the ability of seedlings to emerge from different achene burial depths. Central achenes germinate more rapidly and in higher proportions under a broad spectrum of conditions. On the other hand, germination in peripheral achenes is much more restricted, partly as a result of their thick pericarp; a high proportion of this type of achene does not germinate and remains in a dormant state on the ground, forming a temporary seedbank. Because of the increased size of the embryo, seedlings from peripheral achenes can emerge from greater depths and are initially more vigorous than those from central achenes. Central achenes represent a strategy that facilitates settling in new areas; peripheral achenes represent a strategy that ensures in situ persistence. These biological characteristics are advantageous for colonizing species.     

Growth response of six weed species and spring barley (Hordeum vulgare) to increasing levels of nitrogen and phosphorus

A glasshouse experiment was carried out to investigate the influence of increasing levels of nitrogen and phosphorus on the growth of six common weed species growing alone or in competition with spring barley (Hordeum vulgare). Capsella bursa‐pastoris, Chenopodium album, Papaver rhoeas, Sinapis arvensis, Spergula arvensis, Viola arvensis and spring barley were grown in pots with different levels of nitrogen (0, 30, 60, 90, 120 and 150 kg N ha^?1) or phosphorus (0, 10, 20, 30, 40 and 60 kg P ha^?1). The aboveground parts of the plants were harvested after 7 weeks and the dry weight of shoots, percentage N and P content of the shoot and uptake of N and P were determined. A linear or a polynomial model was used to describe the data. Growing alone, Spergula arvensis was the only weed species that increased its dry weight at the same rate as barley. Weed species with low dry weight increase had larger increases in percentage N or P content than barley, indicating a luxury accumulation of nutrients. The uptake of N and P per pot did not differ much between weeds and barley. V. arvensis and P. rhoeas accumulated least nutrients (per cent of dry matter) and Spergula arvensis accumulated most. Weeds grew poorly in competition with barley. The percentage N and P content in barley did not change when they grew in competition with weeds.     

Competitive ability of five common weed species in competition with soybean

The competitive ability of five prominent weeds species that have the potential to interact in soybean cropping systems of Argentina (Amaranthus quitensis, Chenopodium album, Digitaria sanguinalis, Setaria verticillata and Tagetes minuta) was evaluated in two greenhouse experiments (Exp. 1 and Exp. 2). Crop and weeds were grown in all pairwise mixtures using an additive competition design. Competitive ability was evaluated through competitive indices based on species total biomass. Both experiments showed asymmetric competitive interactions between species, resulting in a competitive network predominantly transitive involving up to four from six species in Exp. 1: Glycine. max > C. album > D. sanguinalis > (A. quitensis, S. verticillata and T. minuta) and up to three from six species in two pathways in Exp. 2: G. max > D. sanguinalis > (C. album, S. verticillata and T. minuta); and G. max > A. quitensis > (C. album, S. verticillata and T. minuta). The hierarchical relationship between species found in this study has implications on weed population dynamics in the context of community assembly framework. We discuss engineered management practices that consider the use of the crop and weed competitive ability to modulate the community structure and the rationalization in the use of herbicides directed to avoid environmental damage.     

Interannual variation in weed biomass on arable land in Sweden

Data were analysed on weed biomass from untreated plots in 2672 field experiments conducted in spring- and autumn-sown cereal and oilseed crops in Sweden 1972–1992. The coefficient of variation (CV) among years in the biomass of annual weeds per square metre was 29% in autumn-sown crops. In spring-sown crops, which had less weed biomass, the corresponding value was 49%. The biomass of summer annuals varied most (105%). Low winter temperatures seemed to increase the biomass of weeds in autumn-sown crops. In spring-sown crops, weed biomass production was higher in years with high rainfall during late spring. Partial ordination (pCCA) of weed data indicated that the interannual variations in autumn-sown crops were mainly manifested by the occurrence of summer annuals. Results from similar ordination of data from spring-sown crops were partly explained by the occurrence of winter annuals.     

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.     

Germination characteristics and emergence time of annual Bromus species of differing weediness in Sweden

The germination ecology of four annual Bromus species, which differ in weediness on arable land in southern Sweden, was investigated. The most problematic species is Bromus sterilis , while Bromus hordeaceus frequently occurs on arable land. In contrast, Bromus arvensis is a rare weed, and Bromus tectorum is found infrequently in fields despite being a widespread ruderal species. Five experiments were conducted to identify germination characteristics that could explain differences in habitat and abundance: (i) intraspecific variation in dormancy level; (ii) germination response to different light conditions; (iii) light and temperature interactions at germination; (iv) timing of seedling emergence; and (v) seed persistence in soil. Bromus sterilis and B. tectorum behaved similarly in all tests. For both these species, there were large differences in dormancy level among populations and strong inhibition of germination by light. In addition, emergence from seeds sown on the soil surface was both delayed and reduced compared with buried seeds. In contrast, B. hordeaceus and B. arvensis showed generally weak dormancy, and germination was only slightly inhibited by light. It was concluded that germination characteristics alone do not explain the differences in weediness between these four species.     

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.     

Effects of winter wheat cultivars and seed rate on the biological characteristics of naturally occurring weed flora

Summary Differential competitive ability of six winter wheat cultivars and traits that confer such attributes were investigated for a range of seed rates in the presence or absence of weeds for a naturally occurring weed flora in two successive years in split-plot field experiments. Crop height and tillering capacity were considered suitable attributes for weed suppression, although competitiveness is a relative rather than an absolute characteristic. Maris Huntsman and Maris Widgeon were the most competitive cultivars whereas Fresco was the least competitive. Manipulation of seed rate was a more reliable factor than cultivar selection for enhancement of weed suppression, although competitiveness of cultivars Buster, Riband and Maris Widgeon was not enhanced by increased seed rate. Crop densities ranging between 125 and 270 plants m⁻² were found to offer adequate weed suppression. Linear relationships were observed between individual and total weed species dry weight and reproductive structures per unit area.     

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。     

Physio-biochemical and nutrient constituents of peanut plants under bentazone herbicide for broad-leaved weed control and water regimes in dry land areas

The abundance of broad-leaved weeds in peanut fields represents the handicap in weed management programs, since limited specific herbicides can be recommended to control them. Moreover, the physio-biochemical constituents and nutritional status in peanut plants as affected by available herbicides, i.e., bentazone under water stress conditions are not well known. Therefore, field trials were conducted during the growing seasons in 2016 and 2017 to investigate the interactional impact of irrigation levels (I₅₀, I₇₅ and I₁₀₀, representing irrigation by 50%, 75% and 100% of crop evapotranspiration, respectively) and weed control practices (bentazone, bentazone+hoeing once, hoeing twice and weedy check as control) on dominant broad-leaved weeds as well as peanut physiological and agronomic traits. Result indicated that the efficiency of weed control for each weeded treatment under I₅₀ significantly equaled with its counterpart under I₇₅ or I₁₀₀. Bentazone+hoeing once diminished weed biomass by 89.3% and enhanced chlorophyll content of peanut plants by 51.2%. Bentazone relatively caused a reduction in carotenoides. Hoeing twice and bentazone+hoeing once under I₁₀₀ in both growing seasons as well as hoeing twice under I₇₅ in 2017 were the superior combinations for boosting pod yield of peanut plants. Treatment of bentazone+hoeing once and I₇₅ recorded the lowest reduction in N utilization percentage and the highest increase in potassium utilization percentage of peanut plants. Eliminating weeds enhanced water use efficiency by 37.8%, 49.6% and 34.7% under I₅₀, I₇₅ and I₁₀₀, respectively. In conclusion, peanut seems to be tolerant to bentazone at moderate water supply, thus it can be safely used in controlling the associated broad-leaved weeds.     

Emergence of four weed species in response to rainfall and temperature

The key to achieving effective weed control is to target them when they are young. Understanding their temperature and moisture requirements for emergence will help growers to develop timely control strategies. This study examined the emergence requirements of four key species: Conyza bonariensis, Sonchus oleraceus, Echinochloa colona and Chloris virgata. Two experiments were conducted in a growth room with temperatures of 25/15 and 30/20°C day/night with a photoperiod of 12 h. The first experiment examined emergence under single rainfall events of 0, 2, 5, 10, 20, 30 and 50 mm. The second experiment examined emergence under accumulated rainfall events of 0 mm, 5 mm × 2 (consecutive) days, 5 mm × 4 days, 5 mm × 6 days, 10 mm × 1 day, 10 mm × 2 days and 10 mm × 3 days. The temperature was not significant on emergence in both experiments. In the first experiment, at least 10 mm of rainfall was required for the emergence of all the species, with significantly higher germination rates at rainfall amounts of >20 mm. In the second experiment, the species had higher emergence rates with accumulated rainfall over consecutive days, rather than single rainfall events of the same amount. The length of time that the soil surface remained above the permanent wilting point, allowing the imbibition of water, was also an important factor. This study has provided information on the drivers for emergence of these species and will assist growers in determining what rainfall events are likely to trigger emergence in the field and make timely weed management decisions.     

皖北高粱田杂草种类及群落特征分析

为明确皖北高粱Sorghum bicolor田杂草发生现状, 于2020年-2021年采用倒置“W”九点取样法对皖北6市52个乡镇田间杂草进行了调查?结果表明, 皖北高粱田共有杂草36种, 属17科, 其中禾本科?菊科?苋科种类最多?优势杂草为稗Echinochloa crus-galli?马唐Digitaria sanguinalis?牛筋草Eleusine indica?狗尾草Setaria viridis等4种, 区域性优势杂草4种, 常见杂草13种, 一般杂草15种?阜阳市杂草的优势度指数最高, Berger-Parker指数为4.89, Simpson指数?Shannon-Wiener指数?Pielou指数均高于其他5市, 优势杂草以稗?马唐?牛筋草?狗尾草?反枝苋Amaranthus retroflexus和苋Amaranthus tricolor为主; 亳州市杂草的优势度仅次于阜阳市, 以稗?马唐?牛筋草?狗尾草和铁苋菜Acalypha australis为主?淮北市杂草的丰富度指数最高, Margalef指数为3.16, 以稗?牛筋草?狗尾草?鸭跖草Commelina communis为主?此外, 青葙Celosia argentea?金色狗尾草Setaria pumila?马齿苋Portulaca oleracea?反枝苋Amaranthus retroflexus及碎米莎草Cyperus iria等5种杂草在部分区域内优势度较高?经聚类分析, 皖北杂草群落分为两组, 阜阳?亳州及宿州3市的杂草聚为第1组, 淮南?淮北市及蚌埠3市的杂草聚为第2组?造成各地市杂草群落差异较大的原因与当地农田管理水平?用药习惯和种植制度等因素关系密切?     

不同种植方式对玉米田杂草群落及生长发育的影响

采取随机区组试验,根据农田杂草群落的生态学原理 ,运用生态学方法,通过玉米苜蓿间种与玉米清种相对照,探讨了间种抗旱植物苜蓿对玉米田杂草群落与生长发育的影响.结果表明:清种玉米田中稗草和红蓼的重要值较高,为优势种,间种苜蓿田中的优势种有红蓼、稗草、苘麻、反枝苋、龙葵、藜;在玉米各生育期,间种苜蓿田中的杂草生物量均低于清种玉米田处理,杂草株高大部分低于清种玉米处理;间种苜蓿穗长、穗行数、行粒数、穗重、穗粒重、百粒重和产量较清种玉米分别增加了6.6%、7.6%、2.2%、 12.28%、9.9%、7.8%和4.3%.认为间种苜蓿能够控制杂草数量,抑制杂草生物量增加,苜蓿有抗旱保水的作用,使玉米产量有所提高.     

The persistence of seeds of 16 weed species over six years in two arable fields

Summary Two experiments have investigated the persistence of 16 arable, annual broad-leaved weed species over 6 years in a silty loam and a clay soil. Small plastic beads were included as an 'inert' comparison. Seeds were broadcast in October on to plots at the start of the experiment, and these were either tine cultivated or ploughed annually thereafter. Plots were sown with either spring or winter wheat. As far as possible, weed seeding was prevented each year. For some species, the seed decline appeared to be slower on the ploughed plots than on the tined plots and in the winter wheat compared with the spring wheat. Seed decline also tended to be slower on the clay soil at Rothamsted than on the silty loam at Long Ashton. Some species declined rapidly (e.g. Brassica napus , Chrysanthemum segetum , Galium aparine , Galeopsis tetrahit ), with annual decline rates in excess of 58%, whereas others declined very little (e.g. Papaver rhoeas decline rate 9%). Most of the other species had decline rates between 20% and 40%. The results are discussed in relation to the development of population dynamics models to predict long-term consequences of alternative weed management strategies.     

Chloris polydactyla (L.) Sw., a perennial Poaceae weed: Emergence, seed production, and its management in Brazil

Experiments were conducted to evaluate the plant emergence and seed production of Chloris polydactyla and the efficacy of herbicides for its control. The plants emerged mainly when the seeds were placed on the soil surface at ≤ 3 cm depth. Isolated plants produced a great amount of seeds. The pre-emergence herbicides, acetochlor, atrazine + simazine, s-metolachlor, alachlor, and trifluralin, were effective for C. polydactyla control. The postemergence herbicides, clodinafop-propargil, haloxyfop-methyl, clethodim, fluazifop- p -butil, tepraloxydim, sethoxydim, and quizalofop- p -tefuril showed satisfactory control of the plants at a 20 cm height with six leaves. During the flowering stage (85 cm plant height), only glyphosate was effective in controlling C. polydactyla .     

The importance of light quality in crop–weed competition

Plant competition is thought to be driven by limiting resources. We propose that plant competition is triggered initially by the red to far-red light ratio (R:FR) originating from neighbouring plants, followed by a series of complex physiological processes, which exclude direct resource competition. Field experiments were conducted in 2005 and 2006 in which maize ( Zea mays ) was grown hydroponically. The effect of R:FR signal being reflected from the leaf surface of Amaranthus retroflexus was isolated by avoiding direct competition for light, water and nutrients. Results showed that the low R:FR reflected from the leaf surface of A. retroflexus did alter the carbon allocation pattern of maize when compared with maize growing free of weeds. Prior to silking, maize grown under low R:FR experienced temporal changes in plant height, persistent changes throughout the sampling period in root and shoot dry weights and rate of leaf appearance, but no changes in leaf area. At silking, low R:FR reduced ear and total plant dry weight. These results support the hypothesis that changes in R:FR acts as an early signal of pending competition by initiating a shade avoidance response. Data from this experiment suggest that once a plant is physiologically triggered into a shade avoidance response, these plants do so at a physiological cost, which may constrain plant development and possibly reduce reproductive fitness.     

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.     

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.     

Cover crops and mulches influence weed management and weed flora composition in strip‐tilled tomato (Solanum lycopersicum)

This study was conducted in the Mediterranean environment of Central Italy from 2011 to 2013 with the aim of evaluating the effects of winter cover crops and their residues on weed composition in a cover crop‐tomato sequence. Treatments consisted of five soil managements (three cover crop species ‐ hairy vetch, phacelia, white mustard, winter fallow mulched with barley straw before tomato transplanting and conventionally tilled soil), two nitrogen fertilisation levels (0 and 100 kg N ha^?1) and two weed management levels (weed free and weedy) on tomato. Cover crop residues were arranged in strips on the soil surface and then used as beds for transplanting the tomato seedlings in paired rows. Rotary hoeing was performed in the bare strips between paired tomato rows. At tomato harvesting, the weed aboveground biomass and density was higher in nitrogen‐fertilised tomato than unfertilised tomato, except in hairy vetch and barley straw that showed similar values. Hairy vetch used as a cover crop and dead mulch was the most suppressive species with the highest production of residues, while phacelia and mustard were not suitable for controlling weeds. The tomato yield was high in nitrogen fertilised and weed‐free treatments, except in barley straw mulch, which showed similar values among the weed management treatments. The mulch strips caused variations in weed species composition that was mainly composed of perennial ruderal weeds, while in tilled soil, the weed flora was dominated by annual photoblastic weeds.