Comparison of different weed management systems and their effects on yield of coconut plantations in Sri Lanka

The influence of five different weed management systems on nut yield of coconut were evaluated to determine an economical and effective method of controlling weeds in coconut plantations in the low country, dry zone in Sri Lanka. Treatments imposed included slashing and mulching around the palms with slash (T1), slashing and removing the slash (T2), application of glyphosate (N-(phosphonomethyl)-glycine) alone at 1.44 kg ai ha⁻¹ (T3), application of glyphosate alone at 2.88 kg ai ha⁻¹ (T4) and cover cropping with Pueraria phaseoloides (T5). All treatments were applied twice a year, except for the cover cropping treatment, T5. Based on a reduction in weed biomass, treatments T3, T4 and T5 were found to be significantly effective over other treatments. Coconut yield was increased significantly ( P  < 0.05) in glyphosate-applied plots at both tested rates. Control of weeds with the lower concentration of glyphosate (1.44 kg ai ha⁻¹) resulted in a 25% increase in nut yield over the uncontrolled weed plots. At this rate, it was found to be the most effective and economical method of controlling weeds in coconut plantations. Cover cropping with Pueraria phaseoloides was effective in controlling weeds in the long-term, but was not economical compared with the glyphosate application.     

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 6: Timeliness of economic decision-making in implementing weed resistance management strategies

BACKGROUND: The introduction of glyphosate‐resistant (GR) crops in the late 1990s made weed control in maize, cotton and soybean simple. With the rapid adoption of GR crops, many growers began to rely solely on glyphosate for weed control. This eventually led to the evolution of GR weeds. Growers are often reluctant to adopt a weed resistance best management practice (BMP) because of the added cost of additional herbicides to weed control programs which would reduce short‐term revenue. This study was designed to evaluate when a grower that is risk neutral (profit maximizing) or risk averse should adopt a weed resistance BMP. RESULTS: Whether a grower is risk neutral or risk averse, the optimal decision would be to adopt a weed resistance BMP when the expected loss in revenue is greater than 30% and the probability of resistance evolution is 0.1 or greater. However, if the probability of developing resistance increases to 0.3, then the best decision would be to adopt a weed resistance BMP when the expected loss is 10% or greater. CONCLUSION: Given the scenarios analyzed, risk‐neutral or risk‐averse growers should implement a weed resistance BMP with confidence that they have made the right decision economically and avoided the risk of lost revenue from resistance. If the grower wants to continue to see the same level of return, adoption of BMP is required. Copyright © 2011 Society of Chemical Industry     

The influence of the soil management systems on aboveground and seed bank weed communities in olive orchards

The biodiversity of farmed landscapes is, in the context of agricultural intensification, a key aspect with regard to improving the sustainability of agroecosystems. Olive groves are undergoing rapid changes because of the spread of intensive farming systems, which may have negative environmental impacts. This paper reports a survey on the aboveground flora and seed banks in five olive groves located in Andalusia (Southern Spain). In this study, the following three management systems have been compared: no‐tillage, with the mowing of spontaneous weedy vegetation; no‐tillage, with the mowing of planted cover crops (Poaceae); and conventional tillage practices. Results showed that coverage and an abundance of vegetation are favored by spontaneous weedy vegetation with mowing management, while the richness of aboveground species was affected by landscape diversity and the presence of edges, which increases the richness and diversity of aboveground flora species in olive groves. Seed bank composition showed a low relationship with aboveground flora in the three cover crop management systems. The multivariate analysis performed pointed to those seed species that have a major influence on the aboveground flora communities of each of the three agricultural systems. The seed bank was clearly impoverished in terms of both abundance and species richness after the long‐term conventional tillage practices. We conclude that the intensive long‐term conventional tillage dramatically reduces weed communities in olive orchards and the subsequent ecosystem services provided by them.     

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 5: Effects of glyphosate-based weed management programs on farm-level profitability

BACKGROUND: Glyphosate‐resistant (GR) crops have changed the way growers manage weeds and implement control strategies. Since the introduction of GR crops, growers in many instances have relied on glyphosate almost exclusively to control a broad spectrum of weeds. This overreliance on glyphosate has resulted in the evolution of glyphosate resistance in some weed species. Growers and scientists are concerned about the sustainability of GR crops and glyphosate. When a grower is making decisions about weed control strategies, economic costs and benefits of the program are primary criteria for selection and implementation. Studies across six states were initiated in 2006 to compare the economics of using a weed resistance best management practice (BMP) system with a grower's standard production system. RESULTS: Resistance BMP systems recommended by university scientists were more costly but provided similar yields and economic returns. Rotation of GR crops resulted in a higher net return (maize and soybean) compared with continuous GR crop (cotton or soybean) or rotating a GR crop with a non‐GR crop (maize). CONCLUSION: Growers can implement weed resistance BMP systems with the confidence that their net returns will be equivalent in the short run, and, in the long term, resistance BMP systems will prevent or delay the evolution of GR weeds in their fields, resulting in substantial savings. Copyright © 2011 Society of Chemical Industry     

Size and composition of the weed seedbank after 7 years of different cover-crop-maize management systems

The objective of this study was to obtain detailed information on the long‐term weed suppression potential of four winter soil cover types included in an arable crop system managed at various input levels. We used weed seedbank size and composition to assess weed suppression potential. A field experiment was established in 1993 as a split‐split‐plot design with four replications, including two tillage systems [a conventional system (CS) including ploughing in the cover crops and a low‐input system (LIS) including no tillage with surface mulching of the cover crops] in the main plots, three mineral nitrogen fertilization rates for the main crop in the sub‐plots and four soil cover types (main crop residue, rye, crimson clover and subterranean clover) in the sub‐sub‐plots. Seedbank sampling took place in winter 2000/01. The weed seedbank was analysed with the seedling emergence method. Data were analysed using anova and multivariate techniques. Results indicated that the seedbank density in the LIS was about five times higher than in the conventional input system. In the CS, use of a rye cover crop resulted in a lower seedbank density with respect to the crop residue treatment (?25%), whereas in the LIS the subterranean clover cover crop decreased weed seedbank density as compared with the other cover crops and the crop residue treatment (?22% on average). Differences in species composition were mainly related to tillage system. Implications for cover crop management and the development of sustainable cropping systems are discussed.     

Correlation between the soil seed bank and weed populations in maize fields

Annual weed populations establish every year from persistent seed banks in the soil. This 3 year study investigated the relationship between the number of weed seeds in the soil seed bank and the resultant populations of major broadleaf and grass weeds in 30 maize fields. After planting the crop, 1 m² areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying to a depth of 100 mm and the weed seeds therein were enumerated. The emerged weed seedlings in the field sampling areas were counted over the following 8 weeks. Up to 67 broadleaf species and five grass weeds were identified, although not all were found at every site and some were specific to a region or soil type. For the most abundant weeds in the field plots, on average 2.1–8.2% of the seeds of the broadleaf species and 6.2–11.9% of the seeds of the grass weeds in the soil seed bank emerged in any one year, depending on the species. Overall, the results showed a strong linear relationship between the seed numbers in the soil and the seedling numbers in the field for all the grasses and for most broadleaf weeds. For some species, like Trifolium repens , only a weak relationship was observed. In the case of Chenopodium album , which had the largest seed bank, there was evidence of asymptotic behavior, with seedling emergence leveling off at high seed numbers. An estimate of the soil seed bank combined with knowledge of the germination and behavior of specific weed species would thus have good potential for predicting future weed infestations in maize fields.     

Influence of hairy vetch seed germination and maturation on weediness in subsequent crops

Hairy vetch is a widely adopted cover crop in the United States. However, hairy vetch can become weedy in subsequent crops as seeds germinate after the cover crop growing season, which is largely attributed to seed dormancy. We conducted two field experiments to determine seed germination, viability and seed production phenology of two common hairy vetch cultivars in Blacksburg and Blackstone, Virginia, US. ‘Groff’ and ‘Purple Bounty’ seed were sown in October 2015 and May 2016 and germination was tracked until June 2017. Subsequently, ungerminated seeds were tested for viability. Both cultivars had <2% germination after the initial germination period, and <1% of seed recovered was still viable at the end of the experiments. We also conducted experiments to determine when these cultivars produce viable seed. Hairy vetch seeds were counted and tested for germination in the spring. Both cultivars produced seed beginning in late‐May, but most seed were not viable until mid‐June in Virginia. Our results indicate that seed dormancy is not the primary cause of hairy vetch weediness in subsequent crops as nearly all germination, 99% of the total germinated seed, occurred during the cover crop growing season. Also, if complete termination occurs before mid‐June in Virginia, it is unlikely viable seed will be added to the seed bank. To better utilise this cover crop species, cultivar selection and proper termination are important to prevent weediness.     

Ecological weed management by cover cropping: effects on weed growth in autumn and weed establishment in spring

Cover crops grown in the period between two main crops have potential as an important component of a system‐oriented ecological weed management strategy. In late summer and autumn, the cover crop can suppress growth and seed production of weeds, whereas the incorporation of cover crop residues in spring may reduce or retard weed emergence. Based on these two criteria, six cover crop species were evaluated for their weed suppressive potential in 2 years of experimentation in the Netherlands. Fodder radish, winter oilseed rape and winter rye had the strongest competitive ability in autumn; the competitive strength of Italian ryegrass was intermediate and white lupin and lucerne were poor competitors. Competitiveness was strongly correlated to early light interception. Surprisingly, doubling the recommended sowing density did not increase weed suppressive ability. Although a poor competitor in the fall, after incorporation in spring, lucerne had the strongest inhibitory effect on seedling establishment, followed by winter oilseed rape and white lupin. Winter rye and fodder radish did not affect seedling establishment, whereas Italian ryegrass was not evaluated because of re‐growth after incorporation. Competition in autumn and subsequent residue‐mediated suppression of weed establishment in spring varied among the cover crop species, with winter oilseed rape offering relatively strong effects during both periods.     

The effect of different tillage systems on the composition of the seedbank

The soil seedbank of a wheat crop grown with four tillage systems (mouldboard plough, disk, chisel and no-tillage) for 3 years was analysed. Density and composition of seedbanks varied according to tillage system and depth. The mouidboard plough crop had seedbanks with the lowest seed density and there was no difference in density or composition at 0-5 cm and 5-10 cm depth whereas no—tillage had a more dense seed bank, especially in the upper part of the soil profile. Diversity of seedbanks also increased from mouidboard plough, to disk, to chisel, to no-titlage, which had the most diverse bank. Therefore, the data strongly support the hypothesis that the systems causing less disturbance allow the build-up of a larger and more diverse soil seed bank.     

Benchmark study on glyphosate-resistant crop systems in the United States. Part 2: Perspectives

A six-state, 5 year field project was initiated in 2006 to study weed management methods that foster the sustainability of genetically engineered (GE) glyphosate-resistant (GR) crop systems. The benchmark study field-scale experiments were initiated following a survey, conducted in the winter of 2005-2006, of farmer opinions on weed management practices and their views on GR weeds and management tactics. The main survey findings supported the premise that growers were generally less aware of the significance of evolved herbicide resistance and did not have a high recognition of the strong selection pressure from herbicides on the evolution of herbicide-resistant (HR) weeds. The results of the benchmark study survey indicated that there are educational challenges to implement sustainable GR-based crop systems and helped guide the development of the field-scale benchmark study. Paramount is the need to develop consistent and clearly articulated science-based management recommendations that enable farmers to reduce the potential for HR weeds. This paper provides background perspectives about the use of GR crops, the impact of these crops and an overview of different opinions about the use of GR crops on agriculture and society, as well as defining how the benchmark study will address these issues.     

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 4: Weed management practices and effects on weed populations and soil seedbanks

BACKGROUND: Weed management in glyphosate‐resistant (GR) maize, cotton and soybean in the United States relies almost exclusively on glyphosate, which raises criticism for facilitating shifts in weed populations. In 2006, the benchmark study, a field‐scale investigation, was initiated in three different GR cropping systems to characterize academic recommendations for weed management and to determine the level to which these recommendations would reduce weed population shifts. RESULTS: A majority of growers used glyphosate as the only herbicide for weed management, as opposed to 98% of the academic recommendations implementing at least two herbicide active ingredients and modes of action. The additional herbicides were applied with glyphosate and as soil residual treatments. The greater herbicide diversity with academic recommendations reduced weed population densities before and after post‐emergence herbicide applications in 2006 and 2007, particularly in continuous GR crops. CONCLUSION: Diversifying herbicides reduces weed population densities and lowers the risk of weed population shifts and the associated potential for the evolution of glyphosate‐resistant weeds in continuous GR crops. Altered weed management practices (e.g. herbicides or tillage) enabled by rotating crops, whether GR or non‐GR, improves weed management and thus minimizes the effectiveness of only using chemical tactics to mitigate weed population shifts. Copyright © 2011 Society of Chemical Industry     

Integration of soil, crop and weed management in low-external-input farming systems

Greater adoption and refinement of low-external-input (LEI) farming systems have been proposed as ways to ameliorate economic, environmental and health problems associated with conventional farming systems. Organic soil amendments and crop diversification are basic components of LEI systems. Weed scientists can improve the use of these practices for weed management by improving knowledge of four relevant ecological mechanisms. First, multispecies crop rotations, intercrops and cover crops may reduce opportunities for weed growth and regeneration through resource competition and niche disruption. Secondly, weed species appear to be more susceptible to phytotoxic effects of crop residues and other organic soil amendments than crop species, possibly because of differences in seed mass. Thirdly, delayed patterns of N availability in LEI systems may favour large-seeded crops over small-seeded weeds. Finally, additions of organic materials can change the incidence and severity of soil-borne diseases affecting weeds and crops. Our research on LEI sweetcorn and potato production systems in central and northern Maine (USA) suggests that these mechanisms can reduce weed density and growth while maintaining crop yields. Low-external-input farming systems will advance most quickly through the application of interdisciplinary research focused on these and other ecological mechanisms.     

Combining physical, cultural and biological methods: prospects for integrated non-chemical weed management strategies

Physical, cultural and biological methods for weed control have developed largely independently and are often concerned with weed control in different systems: physical and cultural control in annual crops and biocontrol in extensive grasslands. We discuss the strengths and limitations of four physical and cultural methods for weed control: mechanical, thermal, cutting, and intercropping, and the advantages and disadvantages of combining biological control with them. These physical and cultural control methods may increase soil nitrogen levels and alter microclimate at soil level; this may be of benefit to biocontrol agents, although physical disturbance to the soil and plant damage may be detrimental. Some weeds escape control by these methods; we suggest that these weeds may be controlled by biocontrol agents. It will be easiest to combine biological control with fire and cutting in grasslands; within arable systems it would be most promising to combine biological control (especially using seed predators and foliar pathogens) with cover‐cropping, and mechanical weeding combined with foliar bacterial and possibly foliar fungal pathogens. We stress the need to consider the timing of application of combined control methods in order to cause least damage to the biocontrol agent, along with maximum damage to the weed and to consider the wider implications of these different weed control methods.     

Vertical distribution, size and composition of the weed seedbank under various tillage and herbicide treatments in a sequence of industrial crops

Investigations were conducted during the 2003, 2004 and 2005 growing seasons in northern Greece to evaluate effects of tillage regime (mouldboard plough, chisel plough and rotary tiller), cropping sequence (continuous cotton, cotton–sugar beet rotation and continuous tobacco) and herbicide treatment on weed seedbank dynamics. Amaranthus spp. and Portulaca oleracea were the most abundant species, ranging from 76% to 89% of total weed seeds found in 0–15 and 15–30 cm soil depths during the 3 years. With the mouldboard plough, 48% and 52% of the weed seedbank was found in the 0–15 and 15–30 cm soil horizons, while approximately 60% was concentrated in the upper 15 cm soil horizon for chisel plough and rotary tillage. Mouldboard ploughing significantly buried more Echinochloa crus‐galli seeds in the 15–30 cm soil horizon compared with the other tillage regimes. Total seedbank (0–30 cm) of P. oleracea was significantly reduced in cotton–sugar beet rotation compared with cotton and tobacco monocultures, while the opposite occurred for E. crus‐galli. Total seed densities of most annual broad‐leaved weed species (Amaranthus spp., P. oleracea, Solanum nigrum) and E. crus‐galli were lower in herbicide treated than in untreated plots. The results suggest that in light textured soils, conventional tillage with herbicide use gradually reduces seed density of small seeded weed species in the top 15 cm over several years. In contrast, crop rotation with the early established sugar beet favours spring‐germinating grass weed species, but also prevents establishment of summer‐germinating weed species by the early developing crop canopy.     

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 1: Introduction to 2006-2008

Glyphosate-resistant (GR) crop technology has dramatically impacted agriculture. The adoption of GR systems in canola, maize, cotton, soybean and sugar beets has been widespread in the United States. However, weed scientists are concerned that growers' current herbicide programs and weed management tactics will affect their sustainability and effectiveness. Without proper management, the potential for weed populations to express a high degree of resistance to glyphosate will adversely impact the utility of glyphosate. In 2005, weed scientists from six universities initiated a long-term research study to assess the sustainability of GR technology. This paper introduces five other articles in this series. Over 150 fields of at least 10 ha were selected to participate in a long-term field-scale study, and each field was split in half. On one-half the grower continued using the current weed management program; on the other half the grower used academic-recommended herbicide resistance best management practices. Field data were collected in 2006-2008 to determine the impact of the two weed management programs on weed populations, diversity, seedbank, crop yields and economic returns. This long-term study will provide invaluable data for determining the sustainability and profitability of diversified weed management programs designed to lower the risk of evolving weed resistance to glyphosate.     

Seed dormancy and soil seedbank of the invasive weed Chenopodium hybridum in north‐western China

Seed dormancy and persistence in the soil seedbank play a key role in timing of germination and seedling emergence of weeds; thus, knowledge of these traits is required for effective weed management. We investigated seed dormancy and seed persistence on/in soil of Chenopodium hybridum, an annual invasive weed in north‐western China. Fresh seeds are physiologically dormant. Sulphuric acid scarification, mechanical scarification and cold stratification significantly increased germination percentages, whereas dry storage and treatments with plant growth regulators or nitrate had no effect. Dormancy was alleviated by piercing the seed coat but not the pericarp. Pre‐treatment of seeds collected in 2012 and 2013 with sulphuric acid for 30 min increased germination from 0% to 66% and 62% respectively. Effect of cold stratification on seed germination varied with soil moisture content (MC) and duration of treatment; seeds stratified in soil with 12% MC for 2 months germinated to 39%. Burial duration, burial depth and their interaction had significant effects on seed dormancy and seed viability. Dormancy in fresh seeds was released from October to February, and seeds re‐entered dormancy in April. Seed viability decreased with time for seeds on the soil surface and for those buried at a depth of 5 cm, and 39% and 10%, respectively, were viable after 22 months. Thus, C. hybridum can form at least a short‐lived persistent soil seedbank.     

Development of chemical weed control and integrated weed management in China

More than 200 species of weeds are infesting main crop fields in China, among which approximately 30 species are major weeds causing great crop yield losses. About 35.8 million hectares of crop fields are heavily infested by weeds and the annual reduction of crop yields is 12.3–16.5% (weighted average). Along with rural economic development, approximately 50% of the main crop fields undergo herbicide application. Chemical weed control has changed cultural practices to save weeding labor in rice, wheat, maize, soybeans and cotton. At the same time, continuous use of the same herbicides has caused weed shift problems and weed resistance to herbicides. Consequently, integrated weed management in main crops is being developed.     

High diversity,expanding populations and purifying selection in phytoplasmas causing coconut lethal yellowing in Mozambique

In this study, the putative phytoplasma species causing coconut lethal yellowing disease in Mozambique and Tanzania were characterized. The 16S rRNA and secA genes were sequenced. Phylogenetic analysis revealed that Mozambican coconut phytoplasmas belong to three different types: ‘Candidatus Phytoplasma palmicola’ 16SrXXII‐A, a second strain that was previously isolated in Tanzania and Kenya (16SrIV‐C), and a third strain that was different from all known lethal yellowing phytoplasma species. The third strain potentially represents a novel species and is closely related to pine phytoplasma. Co‐infection with ‘Ca. Phytoplasma pini’‐related and ‘Ca. Phytoplasma palmicola’ 16SrXXII‐A strains was observed. Furthermore, sequence variation in ‘Ca. Phytoplasma palmicola’ at the population level was consistent with purifying selection and population expansion.