Pathogens and their products affecting weedy plants

There are many natural enemies of weedy plants; among them are plant pathogens. Plant pathogens are capable of affecting plants, in part because of the phytotoxins they produce. Phytoloxins of weedy pathogens are produced in culture media by most of the phytopathogenic fungi of weeds that we have studied. In most cases the phytotoxin(s) usually belongs to a family of related compounds produced by the pathogen. Phytotoxin production in the medium can be optimized by placement of the host extract into the medium. Lethal activity is usually observed in the concentration range of 10^-3-10^-6M. The concept of using these molecules, or derivatives thereof, or related compounds as herbicides, should be explored.     

Uprooting and shearing resistances in the seedlings of four weedy species

For mechanical weeding, the uprooting force of whole seedlings and the shearing force of basal stems were measured in two grass weeds ( Setaria faberi and Echinochloa crus-galli var. crus-galli ) and two broad-leaved weeds ( Chenopodium album and Amaranthus patulus ), using balance-type equipment and a pair of scissors, respectively. Seedlings were grown in plastic pots. Uprooting and shearing experiments were carried out on the 11th, 16th, 21st, and 26th days after sowing. The uprooting force, the shearing force required to fracture the specimen, plant dry matter weight and cross-sectional area exponentially increased as seedlings grew, but the uprooting stress and shearing toughness maintained similar values after the 2nd sampling time, except for the 3rd and 4th sampling times in C. album . The increases in uprooting force and the shearing force required to fracture the specimen were supported by an expansion of the cross-sectional area of stems of the broad-leaved weeds or pseudostems of grass weeds. The higher values of uprooting stress and shearing toughness in C. album were related to an increased area of lignified organs in the basal stems. There was a significant correlation between uprooting and shearing forces. The shearing force was always higher than the uprooting force, so that most seedlings were uprooted and not fractured at the basal stems or pseudostems. The mean ratio of uprooting force to root dry matter weight after the 2nd sampling time suggested a high uprooting resistance at an extremely low amount of root dry matter weight.     

High level of variation among Sri Lankan weedy rice populations,as estimated by morphological characterization

Weedy rice (Oryza sativa f. spontanea) is a notorious weed that infests paddy fields worldwide. Understanding the morphological variation pattern of this weed in a given rice‐planting region will facilitate its effective management and use. Here, 29 populations, covering nearly all the rice‐cultivation regions in Sri Lanka, were characterized in a common‐garden cultivation experiment that was based on 13 morphological traits. The variation level of the weedy rice populations was considerably high, as estimated by the Simpson and Shannon–Weaver indices. An ANOVA revealed a higher level of among‐population variation than within‐population variation. Seed shattering was the most variable trait and the seed length and width were the least variable traits, as indicated by their coefficient of variation. The results of the principal component analysis, in which the first two principal components represented 57.5% of the total variation, indicated the important role of such traits as plant height, seed weight and number of tillers and panicles in the divergence of the weedy rice populations. However, the variation was not associated with their geographical locality. Knowledge of such a morphological variation pattern provides opportunities to design strategic management methods for weedy rice control in Sri Lanka, in addition to the proper use of it as a genetic resource for rice improvement.     

Growth of Parietaria debilis in fallow and in undisturbed areas

Parietaria debilis is a dominant annual weed in many non‐tillage fallow and undisturbed areas in Argentina. Herbicides control P. debilis inconsistently. A study on the growth of P. debilis, in a fallow in a soyabean–maize rotation including glyphosate‐resistant cultivars and in an undisturbed area without crops or weed control, was conducted in the central soyabean area of Argentina. The biomass dynamics of all species in the community, as well as biomass, density and growth traits of P. debilis were assessed. Biomass of several species including P. debilis and total biomass were greater in undisturbed than in fallow plots in both years of the study. Diversity was greater in undisturbed plots in 2000, but no differences in diversity were observed in 2001. In both treatments, P. debilis emergence began in March and finished in October and density increased from March to May. High mortality occurred in June and July, particularly in undisturbed plots. In the fallow plots, no other tall weed species were present and light interception was higher in spring when fruit production was at its peak. Conversely, in the undisturbed plots, P. debilis was substantially taller and had greater leaf area due to lower light interception by the high canopy of the rest of the community. In fallow, P. debilis is favoured by single applications of glyphosate, because the herbicide eliminates competitors. Control, if applied, should be directed to both fallow and undisturbed environments, as the weed produces considerable numbers of seeds and can invade extensively managed areas.     

浙沪小麦田杂草调查及优势杂草化学防除技术研究

为了明确浙沪小麦田杂草发生情况及优势杂草控制技术,采用唐氏五级目测法和随机取样计数法相结合的方法,对上海和浙江的116块冬小麦田杂草进行了抽样调查,同时采用盆栽试验和田间小区试验测定了7种除草剂对主要危害杂草的防效。结果表明,浙沪冬小麦田共调查到杂草43种,隶属于14科,其中菊科杂草种类最多,有10种,其次是禾本科杂草9种,再次是石竹科杂草5种。杂草群落组成以禾本科杂草为主,优势杂草为日本看麦娘Alopecurus japonicus Steud.、菵草Beckmannia syzigachne(Steud.) Fern.、棒头草Polypogon fugax Nees ex Steud.、硬草Sclerochloa dura(L.) Beauv.、早熟禾Poa annua L.、鹅肠菜Myosoton aquaticum(L.) Moench、救荒野豌豆Vicia sativa L.、猪殃殃Galium spurium L.和小藜Chenopodium ficifolium Smith。室内除草活性及田间药效试验结果表明,日本看麦娘可用15%炔草酯WP、5%唑啉草酯EC、30 g/L...     

A definitive method for distinguishing cultivated onion from its weedy mimic,Asphodelus fistulosus,at multiple developmental stages

The onion, Allium cepa, is an important vegetable crop around the world. Globally, India ranks second in onion production, but yields are often much lower than in many other onion producing countries. This study reports on one major contributing factor to low onion yields in India: the presence of a weedy mimic that is morphologically similar to onion until the onset of flowering. We used morphological and molecular methods to identify this mimic as Asphodelus fistulosus, an exotic weed not previously reported in India. Our study indicated that molecular markers derived from the rbcL and/or matK chloroplast genes in a DNA barcoding approach allow accurate identification of this weed using any tissue and even at early developmental stages. Our results also showed that visual examination of seed lots coupled with DNA barcoding analysis of samples of 5–10 individual seeds can be used to confirm identification. The ability to easily identify contaminating material before and during cultivation can allow farmers to minimise production losses and prevent further spreading of this weed.     

我国杂草稻危害现状及其防控对策

随着直播稻和稻麦免、少耕技术的推广,杂草稻在我国的危害越来越重,已严重影响水稻产量和稻米质量.笔者分析了稻田杂草稻的发生危害原因,提出了采用高纯度的种子,从源头上防止杂草稻蔓延和侵入危害;及时清理收割机等农机上携带的杂草稻种子,防止杂草稻的传播;翻耕、诱杀以及手工拔除,轮作、直播改移栽水稻栽培方式;使用化学除草剂防除等综合防除技术.     

广西城市草坪杂草的种群及发生调查

以南宁市为中心,对柳州、北海、桂林、玉林和贺州6个广西主要城市的各类草坪杂草种类及发生规律开展了调查研究。结果表明:广西城市草坪共有杂草21科83种,其中优势杂草种类有19种,菊科、禾本科的优势杂草种类最多,分别占优势种群总数的31.6％和26.3％。向阳地生境草坪主要杂草种类为酢酱草和马唐,背阳地生境草坪主要杂草种类为圆果雀稗和空心莲子草,阴潮地生境草坪主要杂草种类为空心莲子草和水沙草。春季草坪主要杂草科为酢酱科和菊科,夏季草坪主要杂草科为禾本科和酢酱科,秋季草坪主要杂草科为禾本科和莎草科,冬季草坪主要杂草科为石竹科和十字花科。     

Weed flora and weed management in established olive groves in Albania

Weed flora were surveyed during 2000 and 2001 in 10 established olive groves that were located in the area of Vlora, in south‐western Albania. The effectiveness of six weed management treatments (soil tillage, straw mulch, cover cropping [a mixture of rye with peas], and grazing, as well as glyphosate and diuron application) on the weed flora, olive yield, and fruit quality also were investigated in two locations during 2000, 2001, and 2002. More than 80 weed species were recorded, representing a total of 14 families, in which the families Poaceae, Fabaceae, Asteraceae, Ranunculaceae, and Rosaceae predominated. The glyphosate application provided the highest and most consistent level of weed control, whereas diuron achieved sufficient weed control. The straw mulch provided acceptable weed control but the cover crop and the grazing did not sufficiently control the weeds. The highest fruit and oil yields were produced by the trees treated with the straw mulch as a result of the highest mean fruit weight in each year, followed by the soil tillage treatment. However, the olive trees in the plots treated with glyphosate or grazing provided lower or equal, respectively, fruit and oil yields than did those in the untreated plots (control). The results indicated that certain non‐chemical weed control methods, such as straw mulch, can be implemented successfully in established olive groves, providing satisfactory control of weeds and promoting the highest fruit and oil yields.     

施肥对农田杂草生理生态及群落形成的影响综述

本文综述了施肥对农田杂草群落及土壤杂草种子库的影响,并探讨施肥可显著改变农田杂草发生的原因,论证合理的施肥能改善作物与杂草之间的关系,有效控制一些恶性杂草的发生,保持生物多样性。梳理了农田杂草研究的一些新的发展方向,并认为农业生态系统中施肥对杂草群落的演替、优势杂草种群的确定及其生理生态和遗传进化规律的影响是今后研究的重点和难点。     

Weed flora and soil seedbanks in fields dominated by Imperata cylindrica in the moist savannah of West Africa

Imperata cylindrica (L.) Raeuschel is a dominant and infamous grass weed in the savannah of West Africa. Research to reduce the weed to non-damaging levels is a priority activity at many agricultural institutions. The successful development and implementation of long-term I. cylindrica management strategies depend on the ability to predict changes in weed composition after I. cylindrica has been controlled effectively. The weed flora and soil seedbank were assessed from 329 fields dominated by this species in the fringes of the humid forest (HFF), coastal/derived savannah (CDS) and in the southern Guinea savannah (SGS) in 1996 and 1997. The objectives of the study were to correlate species composition of the weed flora with that of the soil seedbank and to determine the effect of management factors and soil properties on the composition of the weed flora. Species richness in the weed flora and in the weed seedbank was higher in the SGS than in the CDS and HFF. Mean weed density per field was generally higher in the HFF (156 ± 25.0 weeds m^–2) than in the CDS (108 ± 8.1 weeds m^–2) and in the SGS (92 ± 6.3 weeds m^–2). Weed composition varied with agroecological zone as well as with management factors and soil properties. Sørenson's index of similarity was low (mean=0.20) in all zones, indicating poor similarity between the weed flora above-ground and the soil seedbank.     

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.     

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.     

杂草稻的发生及其控制措施

杂草稻的发生与耕作方式、栽培方式等因素有关.杂草稻不仅严重影响水稻的产量,而且降低水稻的商品价值.应采取预防、调整耕作栽培方式以及化学防除的杂草稻综合防治措施对杂草稻进行积极的控制.     

黑龙江垦区杂草稻分布与发生

近几年黑龙江省农垦地区寒地水稻移栽面积迅速扩大,至2008年已经超过100万hm^2,化学除草面积覆盖率达到100％。但杂草稻由于与水稻生物学特性相近,药剂难以防除,危害面积越来越大。杂草稻有长芒、短芒和无芒,多为长芒。芒色有红色和白色两种,数量相当。种皮颜色有黑色、褐色、赤褐色、黄色,多为赤褐色。叶色有绿色和褐色,多为绿色。杂草稻在1—3cm水层下出苗率高于栽培稻。杂草稻具有较强的越冬能力。     

Weed seed movement and dispersal strategies in the agricultural environment

This paper reviews the current knowledge on weed seed movement in an agricultural environment. Seed movement is analyzed both from an agronomic and ecological perspective, focusing predominantly on horizontal seed movement. Abiotic (anemochory and hydrochory), as well as biotic (autochory, myrmecochory, epizoochory, and endozoochory) weed seed dispersal typologies are examined, highlighting the mechanisms involved, the specializations displayed by weed species that have evolved by exploiting a particular dispersal mechanism, and their adaptive interaction with the surrounding ecosystem. Emphasis is also placed on the crucial role of human activity (anthropochory), which can affect natural (biotic and abiotic) weed seed dispersal at several stages, partly via the worldwide commercial seed trade but, above all, by crop management operations, thereby potentially facilitating the entry and spread of alien weed species. This phenomenon, together with the invasive expansion of existing weeds that more successfully coevolve and adapt to the new environment, might exert an adverse effect on biodiversity. In-depth knowledge of weed seed dispersal, survival, and germination mechanisms is therefore essential for effective and eco-compatible management of the weed phytocoenoses present in the agroecosystem in order to promote a rational trade-off between agricultural productivity and environmental protection.