Integrated Weed Management Systems Research Articles

Application method of nitrogen fertilizer affects weed growth and competition with winter wheat

The management of crop fertilization may be an important component of integrated weed management systems. A field study was conducted to determine the effect of various application methods of nitrogen (N) fertilizer on weed growth and winter wheat yield in a zero‐tillage production system. Nitrogen fertilizer was applied at 50 kg ha−1 at the time of planting winter wheat over four consecutive years to determine the annual and cumulative effects. The nitrogen treatments consisted of granular ammonium nitrate applied broadcast on the soil surface, banded 10 cm deep between every crop row, banded 10 cm deep between every second crop row, and point‐injected liquid ammonium nitrate placed between every second crop row at 20 cm intervals and 10 cm depth. An unfertilized control was also included. Density, shoot N concentration and the biomass of weeds was often lower with subsurface banded or point‐injected N than with broadcast N. The winter wheat density was similar with all N fertilizer application methods but wheat shoot N concentration and yield were consistently higher with banded or point‐injected N compared with broadcast N. In several instances, the surface broadcast N did not increase the weed‐infested wheat yield above that of the unfertilized control, indicating that it was the least preferred N application method. Depending on the weed species, the weed seedbank at the conclusion of the 4 year study was reduced by 29–62% with point‐injected N compared with broadcast N. Information gained from this study will be used to develop more integrated weed management programs for winter wheat.

The economic value of pasture phases in the integrated management of annual ryegrass and wild radish in a Western Australian farming system

Most cropping farms in Western Australia must deal with the management of herbicide-resistant populations of weeds such as annual ryegrass (Lolium rigidum Gaudin) and wild radish (Raphanus raphanistrum�L.). Farmers are approaching the problem of herbicide resistance by adopting integrated weed management systems, which allow weed control with a range of different techniques. One important question in the design of such systems is whether and when the benefits of including pasture in rotation with crops exceed the costs. In this paper, the multi-species resistance and integrated management model was used to investigate the value of including pasture phases in the crop rotation. The most promising of the systems examined appears to be so-called 'phase farming', involving occasional 3-year phases of pasture rather than shorter, more frequent and regular pasture phases. This approach was competitive with the best continuous cropping rotation in a number of scenarios, particularly where herbicide resistance was at high levels.

The economic value of haying and green manuring in the integrated management of annual ryegrass and wild radish in a Western Australian farming system

Most cropping farms in Western Australia must deal with the management of herbicide-resistant populations of weeds such as annual ryegrass (Lolium rigidum) and wild radish (Raphanus raphanistrum). Farmers are approaching the problem of herbicide resistance by adopting integrated weed management systems, which allow weed control with a range of different techniques. These systems include non-herbicide methods ranging from delayed seeding and high crop seeding rates to the use of non-cropping phases in the rotation. In this paper, the Multi-species RIM (resistance and integrated management) model was used to investigate the value of including non-cropping phases in the crop rotation. Non-crop options investigated here were haying and green manuring. Despite them providing excellent weed control, it was found that inclusion of these non-cropping phases did not increase returns, except in cases of extreme weed numbers and high levels of herbicide resistance.

The use of thermal time to model common lambsquarters (Chenopodium album) seedling emergence in corn

A mathematical model was developed to predict common lambsquarters seedling emergence in southwestern Quebec. The model was based on the thermal-time concept, using air temperatures in the double-sine calculation method. The model was built using data from five experiment-years for corn naturally infested with weed populations. Once developed, the model was calibrated using different crop seedbed preparation times. The base temperature was then adjusted for each time of seedbed preparation. A power regression function was used to relate adjusted base temperatures and the accumulated thermal units at seedbed preparation time. A modified Weibull function was then fitted to the field emergence data, expressed as the cumulative proportion of the total seedling emergence over the growing season as a function of cumulative thermal units. The simplicity and accuracy of this model would make it an excellent tool to predict common lambsquarters seedling emergence in field situations, facilitating the determination of the timing of scouting in integrated weed management systems.

Influence of nitrogen and duration of weed interference on corn growth and development

Abstract An improved understanding of the effects of nitrogen (N) on crop–weed interactions is needed for the development of integrated weed management systems where responsible use of N fertilizers is considered. Field experiments conducted in 1999 and 2000 at two locations in eastern Nebraska quantify the effects of N and increasing duration of weed interference on corn growth and development. A naturally occurring population of weeds was allowed to compete with the corn crop for increasing lengths of time and at three rates of N application (0, 60, and 120 kg N ha−1). Weed interference and withholding applied N increased the time to 50% silking by an average of 3.9 and 2.9 d, respectively. Regardless of treatments, relative growth rates of corn leaf area and biomass were maximized between the V1 and V2 growth stages of corn and increased linearly with N rate but were affected to a lesser extent by weed presence. The improvement in early season corn growth with addition of N resulted in greater leaf are...

Developing weed-suppressive soils through improved soil quality management

Manipulating soil microbial communities using soil and crop management practices is a basic strategy in developing sustainable agricultural systems. Sustainable farming is based, in part, on the efficient management of soil microorganisms to improve soil quality. However, the identification of biological indicators of soil quality that can be used to predict weed suppression in soils has received little attention. We investigated differences in soil microbial activity among various crop and soil management systems to assess: (i) the microbiological characteristics of these soils; (ii) determine whether any relationships existed that might be used in the development of weed suppression. Soil enzyme activity, water-stable aggregates, and the proportions of weed-suppressive bacteria were compared among seven cropping systems and one native-prairie ecosystem in mid-Missouri, USA. Assays of soil enzymes (fluorescein diacetate hydrolase, dehydrogenase, phosphatase) revealed that organic and integrated cropping systems, and the native-prairie ecosystem had the highest levels of soil activity. Weed rhizospheres from these same ecosystems also had greater proportions of bacterial isolates characterized as “growth suppressive” to green foxtail ( Setaria viridis [L.] Beauv.) and field bindweed ( Convolvulus arvensis L.): 15 and 10%, respectively. The proportion of water-stable soil aggregates was the greatest in soils with the highest organic matter and was found to be related to higher enzyme and weed-suppressive activity. Selected biological indicators of soil quality were associated with potential weed-suppressive activity in soil when that soil was managed for high organic matter content under reduced tillage systems. This research study provides further evidence that soil quality and sustainable agricultural practices may be linked to integrated weed management systems for the biological suppression of weeds.

Seeding rate, herbicide timing and competitive hybrids contribute to integrated weed management in canola (Brassica napus)

Implementing a favourable agronomic practice often enhances canola production. Combining several optimal practices may further increase production, and, given greater crop health and competitiveness, could also improve weed control. A field experiment was conducted at Lacombe and Lethbridge, Alberta, from 1998 to 2000, to determine the optimal combination of glufosinate-tolerant cultivar (hybrid InVigor 2153 or open-pollinated Exceed), crop seeding rate (100, 150, or 200 seeds m-2) and time of weed removal (two-, four-, or six-leaf stage of canola) for canola yield and weed suppression. At equal targeted seeding rates, the hybrid cultivar had greater seedling density (8 plants m-2 higher) and seed yield (22% higher) when compared with the open-pollinated cultivar. Combining the better cultivar with the highest seeding rate, and the earliest time of weed removal led to a 41% yield increase compared with the combination of the weaker cultivar, the lowest seeding rate and the latest time of weed removal. The same optimal factor levels also favoured higher levels of weed control and lower weed biomass variability. Managing these factors at optimal levels may help increase net returns, reduce herbicide dependence and favour the adoption of more integrated weed management systems. Key words: Crop health, direct seeding, glufosinate, integrated weed management, weed population variability

Densidade e características morfológicas de plantas de picão-preto na previsão de perdas de rendimento de grãos de soja por interferência

A utilização de sistemas para manejo integrado de plantas daninhas depende da habilidade em se prever o impacto da infestação de plantas daninhas no potencial de rendimento de grãos da cultura. O objetivo deste trabalho foi comparar diferentes variáveis explicativas para uso no modelo da hipérbole retangular, a fim de identificar aquela que forneça melhor previsão da interferência de picão-preto (Bidens pilosa e Bidens subalternans, em infestações mistas) em soja. Foram realizados experimentos em dois ambientes, localizados em Passo Fundo e Eldorado do Sul, RS. Utilizaram-se densidades variáveis de picão-preto e três épocas de semeadura da soja (3, 7 e 11 dias após a dessecação da cobertura vegetal das áreas). Avaliou-se a densidade das plantas daninhas aos 20 e 30 dias após a emergência da soja (DAE) e na pré-colheita e características morfológicas de plantas de picão-preto, como densidade de folhas, área foliar e cobertura foliar do solo aos 20 DAE. Constatou-se que a variável explicativa densidade de plantas de picão-preto propiciou ajustes satisfatórios do modelo; no entanto, ela não integra os efeitos de ambientes e de épocas de semeadura da cultura, diferentemente do que ocorreu para as características morfológicas. Dentre estas, destacam-se a densidade de folhas e a de área foliar como as de maior potencial de utilização como variáveis explicativas na previsão da perda de rendimento de grãos de soja por interferência de picão-preto.

Glyphosate‐resistant soybean as a weed management tool: Opportunities and challenges

Transgenic soybean, resistant to glyphosate, represents a revolutionary breakthrough in weed control technology. Transgenic soybean is the most dominant among all transgenic crops grown commercially in the world. In 2000, glyphosate‐resistant (GR) soybean was planted to 25.8 million hectares globally, which amounts to 58% of the total global transgenic crop area. The United States soybean area planted with GR soybean has increased from 2% in 1996 to 68% in 2001. Glyphosate‐resistant soybean as a weed management tool has provided farmers with the opportunity and flexibility to manage a broad spectrum of weeds. The use of glyphosate in GR soybean offers another alternative to manage weeds that are resistant to other herbicides. The rapid increase in GR soybean area is caused by the simplicity of using only one herbicide and a lower cost for weed control. Adoption of GR soybean has resulted in a dramatic decrease in the area treated with other herbicides. Glyphosphate‐resistant soybean should not be relied on solely to the exclusion of other weed control methods, and should be used within integrated weed management systems. Over‐reliance on GR soybean could lead to problems such as shifts in weed species and population, and the development of glyphosate‐resistant weeds. The challenge is for soybean farmers to understand these problems, and for weed scientists to communicate with farmers that continuous use of glyphosate may diminish the opportunity of GR soybean as a weed management tool in the future.

Stability Indices for Weed Management Systems in Forage Oat (Avena sativa L.)

A set of integrated weed management systems was assessed in forage oat (Avena sativa L.), cv. Kent, to compare efficiencies inter se in terms of mean forage productivity over different locations and different years, and relative agronomic effectiveness. Results for seven weed management systems were obtained for three consecutive years, i.e. 1995–96, 1996–97 and 1997–98, at five locations of the Indian subcontinent. Two systems – use of weeder‐cum‐mulcher at the 3‐ and 6‐week crop stages (WCS) and use of weeder‐cum‐mulcher at the 4 WCS plus application of 2, 4‐D at 0.37 kg a.i. ha–1 at 6 WCS – were found to be effective and consistent over locations from year to year and over years from location to location. Pooled analysis over years and locations showed manual weeding at 4 WCS plus application of 2, 4‐D at 0.37 kg a.i. ha–1 at 6 WCS, on the one hand, and use of weeder‐cum‐mulcher at 3 WCS plus manual weeding at 5 WCS, on the other, to have equal efficiencies and to be more beneficial than the other treatments. Recommendation of the latter system is of particular interest as this system merely involves mechanical operations which provide the benefits of soil mulching and carry no risk of biotoxicity due to herbicides in crop plants or adverse effects on soil through uninterrupted use of chemicals.

Oxidation of phenolic acid derivatives by soil and its relevance to allelopathic activity.

Previous studies have suggested that phenolic acids from legume green manures may contribute to weed control through allelopathy. The objectives of this study were to investigate the oxidation reactions of phenolic acids in soil and to determine the subsequent effects of oxidation upon phytotoxicity. Soils were reacted for 18 h with 0.25 mmol L(-1) benzoic and cinnamic acid derivative solutions and Mn release from the suspension was used as a marker for phenolic acid oxidation. The extent of oxidation in soil suspensions was in the order of 3,4dihydroxy- > 4-hydroxy-3-methoxy- > 4-hydroxy-approximately 2-hydroxy-substituted benzoic and cinnamic acids. The same ranking was observed for cyclic voltammetry peak currents of the cinnamic acid derivatives. This suggests that the oxidation of phenolic acids is controlled by the electron transfer step from the sorbed phenolic acid to the metal oxide. A bioassay experiment showed that the 4-hydroxy-, 4-hydroxy-3-methoxy-, and 3,4-dihydroxy-substituted cinnamic acids were bioactive at 0.25 mmol L(-1) concentration. Reaction with soil for 18 h resulted in the elimination of bioactivity of these three cinnamic acids at the 5% significance level. The oxidative reactivity of phenolic acids may limit the potential of allelopathy as a component of an integrated weed management system. However, the initial phytotoxicity after soil incorporation may coincide with the early, critical stage of weed emergence and establishment, so that allelopathic phenolic acids may still play a role in weed management despite their reactivity in soil systems.

Biological control of weeds by means of plant pathogens: Significance for integrated weed management in modern agro-ecology

Biological control of weeds by using plant pathogens has gainedacceptance as a practical, safe, environmentally beneficial, weedmanagement method applicable to agro-ecosystems. The interest in thisweed control approach from public and private groups, and support forresearch and developmental effort, are on the upswing. This increasinginterest is stimulated largely due to major economic, social, andenvironmental forces that are directing our choices in crop productionpractices. Some of these changes are market-driven while others aresocial and ecological in nature. These changes are in turn influencingthe choices in weed control methods. In this regard, biocontrol withplant pathogens has been proven a feasible, albeit minor, component ofmodern integrated weed-management systems. This environmentallybeneficial method should be promoted and exploited further to meet thecurrent and future challenges in weed management in agro-ecosystems.

Theoretical and practical challenges to an IPM approach to weed management

Modern weed control tactics have played a major role in the productivity of cropping systems. Herbicides have been an effective component of weed control for major crops, greatly reducing yield losses and facilitating reduced tillage systems. Although these benefits are important, weed problems, soil erosion, and environmental concerns persist. Herbicides will continue to play a key role in most production systems, but weed species will continue to evolve and weed communities shift in response to selection pressures. Weed science must develop and incorporate additional practices to create integrated management systems that diversify selection pressures and reduce environmental degradation. Integrated pest management (IPM) may provide a useful framework for the development of integrated weed management systems. The basic principles of IPM are well established and have been successfully applied to many agricultural pests. However, the application of IPM to weed management has lagged behind other pest management disciplines. Many of the concepts and approaches of IPM are relevant to weed management, but these were not developed specifically for weed management and are not sufficient to address it adequately. Principles of IPM unique to weed management need to be delineated, developed, and put into practice. Although IPM for other pests provides an excellent framework, weed science must develop its own theory, management tactics, and monitoring procedures based on the unique characteristics of weed communities.

Why glyphosate is a global herbicide: strengths, weaknesses and prospects

After 25 years of sales, glyphosate (N-(phosphonomethyl)glycine) is the world's biggest selling and fastest growing agrochemical. Glyphosate has many strengths, particularly its systemicity and ability to control perennial weeds, which have facilitated its role as an essential tool in modern agriculture. Surveys of recent scientific and patent literature point to several key areas of current and future interest in glyphosate and its use. Biotechnology topics have been the most popular, but there is still much interest in the molecule per se, particularly in manufacturing processes. The mode of action and physiology of glyphosate are common subjects. More applied aspects concern the development of formulations with new adjuvants, or mixtures with other herbicides, to enhance performance. An increasing number of papers are reporting on its environmental fate and on agronomic techniques designed to improve the efficiency of application and minimise its environmental impact. Lack of weed resistance is a key feature of glyphosate despite its widespread use. However, differential levels of tolerance between species have led to changes in weed succession. There is a need to develop integrated weed management systems in which glyphosate still plays a key role. Glyphosate is an exceedingly effective herbicide and presents a considerable challenge to the development of new herbicides for sustainable cropping systems and situations in which cost-effective and environmentally considerate weed control is required. © 2000 Society of Chemical Industry

Why glyphosate is a global herbicide: strengths, weaknesses and prospects

After 25 years of sales, glyphosate (N-(phosphonomethyl)glycine) is the world's biggest selling and fastest growing agrochemical. Glyphosate has many strengths, particularly its systemicity and ability to control perennial weeds, which have facilitated its role as an essential tool in modern agriculture. Surveys of recent scientific and patent literature point to several key areas of current and future interest in glyphosate and its use. Biotechnology topics have been the most popular, but there is still much interest in the molecule per se, particularly in manufacturing processes. The mode of action and physiology of glyphosate are common subjects. More applied aspects concern the development of formulations with new adjuvants, or mixtures with other herbicides, to enhance performance. An increasing number of papers are reporting on its environmental fate and on agronomic techniques designed to improve the efficiency of application and minimise its environmental impact. Lack of weed resistance is a key feature of glyphosate despite its widespread use. However, differential levels of tolerance between species have led to changes in weed succession. There is a need to develop integrated weed management systems in which glyphosate still plays a key role. Glyphosate is an exceedingly effective herbicide and presents a considerable challenge to the development of new herbicides for sustainable cropping systems and situations in which cost-effective and environmentally considerate weed control is required. © 2000 Society of Chemical Industry

Effect of barley plant density on wild oat interference, shoot biomass and seed yield under zero tillage

There has been little research aimed at developing regression models to describe the effects of barley and wild oat plant density on barley yield loss, or wild oat biomass and seed yield. Such models are an important component of integrated weed management systems, and can help determine when weed control with herbicides is economical. Field experiments were conducted over 4 yr at Vegreville, Alberta, to determine the interactive effects of wild oat and barley plant density on barley and wild oat variables in a zero tillage system. A nonlinear regression model in most cases provided good descriptions of barley yield loss, wild oat shoot dry weight, and wild oat seed yield as functions of wild oat and barley plant densities. The interactive effect of wild oat and barley plant density on percentage barley yield loss did not differ significantly (P = 0.05) among years. A pooled regression model describing barley yield loss accounted for 57% of the variation, and provides a means of estimating yield loss due to wild oat in barley grown under zero tillage. Barley yield loss increased as wild oat density increased but the magnitude of the yield loss diminished with increasing barley plant density. Wild oat economic threshold densities varied among years, and were strongly influenced by barley price and expected wild oat-free yield. Economic thresholds were greater at higher barley plant densities. Barley seed weight decreased with increasing barley plant density, and to a lesser extent with increasing wild oat density. The interactive effect of wild oat and barley plant density on wild oat seed yield varied significantly with year, and appeared to be influenced by climatic conditions. The cooler, wetter spring of 1996 favored wild oat seed production (by several orders of magnitude) compared with the relatively warmer and drier spring of 1995. Each year wild oat seed yield and shoot dry weight decreased as barley plant density increased. The results suggest that seeding barley at relatively high rates may reduce the need for wild oat control with herbicides in zero tillage systems. Key words: Zero tillage, wild oat interference, barley seeding rate, nonlinear regression

Fundamentals of Weed Science

Robert Zimdahl has produced an update of his excellent book Fundamentals of Weed Science. This text is directed at students or others who require, not a handbook on weed control, but a comprehensive overview of the principles of weed science. While there are many weed science textbooks, Zimdahl is unique in his use of weed ecology as the central theme. He also adds topics unusual in a standard text, including chapters on ethnobotany and pesticide legislation. Weed science is much more than simply selecting which herbicide to apply in a given crop. This book is successful in giving a flavour of the breadth of disciplines involved in the management of these fascinating plants, from ecology to agronomy, botany, organic chemistry and molecular biology. Most importantly, the underlying emphasis on weed ecology provides a means of understanding the behaviour of these species, as well as a foundation on which to build the principles and practices of integrated weed management systems. Chemical control is not neglected, however. Herbicides and their use are an important management tool, and there is adequate coverage of herbicide classification, mode of action, application, formulation, safety and environmental impact. Other methods are also described and updated in this new edition to include recent advances in weed control techniques. The final chapter is a personal overview by the author on the future of weed science. It focuses on research needs, again with a strong ecological emphasis, and on trends, in particular the development of herbicide resistant crops. It also discusses the politics which influence weed management and weed science research. The breadth of the subject matter is, unfortunately, offset by the relatively superficial coverage of each topic, though this is remedied to an extent by the comprehensive reference lists given in each chapter, which give the reader a pointer to where to look for more information. The book is written in an easy, casual style, and a peppering of quotations (from Shakespeare to Emerson, The Bible and Victor Borge) lighten what could otherwise be sometimes dense subject matter. It is a good read. The addition of more drawings and plates would have been an added benefit. The one major drawback to the book is that it is written for a North American audience. The use of common names (despite a glossary at the end of the book) is a constant irritation to a non-American reader, and many of the examples given (e.g. the weed management systems and the chapter on pesticide legislation) are based entirely on the USA. The book contains little information specific to Europe, and almost none on tropical countries. Despite this, the book still represents one of the best introductions to the ‘fundamentals of weed science’ and it should be high on the list of recommended reading for students.

A Risk Management Perspective on Integrated Weed Management

Abstract The variability inherent in agriculture influences many crop production decisions made by farmers, including weed management. This paper addresses how farmers perceive the variability, or risk, associated with integrated weed management systems in terms of yield, economic returns, and time and labor management. This paper addresses how key biological time constraints such as periodicity of weed emergence, rate of crop growth and development, and critical periods of weed control can influence the outcome of integrated weed management systems. A key component to developing successful integrated weed management systems lies in the ability of the crop producer to align individual time and labor management issues with existing biological time constraints.

Seasonal abundance and spatial pattern ofSetaria faberi, Chenopodium album, andAbutilon theophrastiin reduced-tillage soybeans

A better understanding of the influence of various crop and weed management practices on spatiotemporal dynamics of weeds could improve the design of integrated weed management systems. We examined the influence of 18- and 76-cm soybean row spacings on emergence pattern and spatial aggregation of giant foxtail, common lambsquarters, and velvetleaf seedling cohorts. In addition, we characterized the soil seedbank and determined the quantitative and spatial relationship between the seedbank and seedling populations. Viable seeds of about 10 weed species and twice as many species of seedlings were identified in the weed community. Giant foxtail and common lambsquarters were the predominant species in the seedling and seedbank population, respectively, each accounting for 60 to 70% of the total weed species density. Emergence of giant foxtail, common lambsquarters, and velvetleaf depleted 12 to 33%, < 2% and 12 to 49% of the seedbank in the upper 10 cm of the soil profile. Peak time and periodicity of weed emergence was not influenced by soybean row spacing, and peak time of emergence of giant foxtail, common lambsquarters, and velvetleaf occurred 3 to 4, 3 to 6, and 3 to 9 weeks after soybean planting (WAP), respectively. Magnitude of giant foxtail emergence 5, 6, and 9 WAP was 98, 96, and 76% greater in 76- than in 18-cm row soybeans only when the population of 76-cm row soybeans was 57% lower than the 18-cm soybeans in 1997. Giant foxtail and common lambsquarters seeds in the seedbank were aggregated in 1996 and 1997 according to the Taylor power law (TPL) and the negative binomial distribution (NBD). The TPL and the NBD were similar in describing the spatial aggregation of giant foxtail and common lambsquarters but not some velvetleaf seedling cohorts. The spatial aggregation of seedlings varied among cohorts for different weed species and was likely due to species-specific biological characteristics that influence seed dispersal, germination, and seedling emergence. Within a 1.5-ha area, aggregation declined with decreasing density. Within a 24-m2area, the level of aggregation of all weed species decreased as seedling densities increased. These results indicated that soybean row spacing influenced neither weed emergence pattern nor weed spatial aggregation; thus, several management decisions can be similar in 18- and 76-cm row soybeans.

Influence of temperature, photoperiod, and irradiance on the phenological development of common ragweed (Ambrosia artemisiifolia)

Implementation of an integrated weed management system requires prediction of the effect of weed competition on crop yield. Predicting outcomes of weed competition is complicated by genetic and environmental variation across years, locations, and management. Mechanistic models have the potential to account for this variability. Weed phenological development is an essential component of such models. Growth cabinet studies were conducted to characterize common ragweed's phenological response to temperature, photoperiod, and irradiance. Ragweed development occurred over a temperature range of 8.0 to 31.7 C, and this response to temperature was best characterized using a nonlinear function. A maximum leaf appearance rate of 1.02 leaves d−1occurred at 31.7 C. Ragweed has a short juvenile phase, during which it was not sensitive to photoperiod. Following this juvenile phase, sensitivity to photoperiod was constant and continued until pistillate flowers were observed. Photoperiods of 14 h or less were optimal and resulted in maximum rates of development. Irradiance level affected ragweed phenological development only when combined with the additional stress of low temperatures. Data generated in this study can be used for the development of mechanistic weed competition models.