Populations Of Weed Species Research Articles

Diversity and Prediction of Corn Product Loss Due Weed Competition to Two Types of Dry Land Agroecosystem

The aim of the study was to determine which weed species had a significant effect on the reduction of maize yields, so that it could be determined which species should be controlled and which should not be controlled. The research was carried out using a descriptive method on dry land in Mumbul Sari Village, Bayan, North Lombok. Collecting data on population and growth of weeds and plants, using sample plots measuring 1 m2 placed at 10 points by random sampling. Parameters observed were weed species population, corn crop population plot-1, dry biomass weight of plot-1 weed, dry biomass weight of plot-1 corn, and dry seed weight of corn plot-1. Quantitative data analysis by calculating the value, relative density (RN), relative frequency (RF) and relative dominance (RD) to calculate the significant value index (SVI), and Summe Diminance Ratio (SDR). There were 2 species of puzzle weed, 10 species of Poaceae weed and 13 species of broadleaf weed. One species of puzzle weed, namely Cyperus rotondus and 3 species of Poaceae Digitaria longiflora, Paspalum conjugatum and Panicum repens, and 2 species of broadleaf weed, Amaranthus spp., and Synedrella nodiliflora, were very dominant and continued to exist during plant growth with respective SDR values each species 10.43%; 15.37%; 10.20%; 9.67 %; 10.00% and 5.80%. The competitiveness and relative weighted dominance of the 6 weed species were higher than other weed species, so that the six weed species were able to eliminate the average maize yield since the plants were 30 – 90 as much as 17.90%; 16.78%; 12.35%;10.88%; 9.18% and 3.40%

GENETIC VARIATION IN WEED SEED DORMANCY AND THEIR MANAGEMENT IN CROPS: A REVIEW

Evolution in the seed dormancy depends on the presence of heritable variation in weed populations. This genetic variation in weeds arises because of abundant, grow rapidly, and produce large numbers of off springs. Compared with other plant species, populations of weed species frequently show limited genetic variation in seed dormancy due to colonization, extensive clonal propagation, inbreeding, and the relative environmental homogeneity. Nevertheless, populations of weed species contain substantial store of genetic variation and genetic differentiation for seed dormancy and other reproductive traits because of pervasive feature of widely distributed nature of weed species. As a result, high level of genetic diversity among the weeds is fostered by hybridization, habitat longevity, environmental heterogeneity, outcrossing and large population size. The objective of this review is to update the existing literature concerned with genetic variation in seed dormancy and reproductive traits in weeds.

Developing Automated and Autonomous Weed Control Methods on Vegetable Crops in New Zealand

Controlling weeds in NZ vegetable crops faces serious problems in the near future: the loss of low-wage staff availability to conduct the labour intensive efforts in spraying, mowing or mulching; the loss of certain herbicides as low cost tools for vegetable crop growers; the resistance built-up in the weed species population against often used herbicides such as glyphosates; the banning of certain ‘problem-herbicides’ as requirements from registration authorities or from the value chain. In addition, strategic decisions of the NZ industry about the way vegetable crops are grown and produced will reduce options for herbicide based weed control. To address these growing concerns, dedicated mechanisms to control weeds in NZ vegetable crops will be studied in this project utilizing the new options provided by automated actions or robotic platforms. The efficacy and the value proposition of such weed management will be determined. The research will cover at least: (i) sensor controlled, targeted herbicide application, (ii) mechanical removal (cutting, plucking, shot blasting...), (iii) electric weeding, and (iv) guided tines, autonomously carried through the crop field and their integration into the standard management of the inter-row/row spaces.

The effect of weed management systems and location on arable weed species communities in glyphosate‐resistant cropping systems

AbstractQuestionHow do different weed management systems based on glyphosate‐resistant (GR) crops affect weed community structure and composition?LocationA total of 156 agricultural fields across six US states.MethodsFields were selected and categorized into three weed management systems based on a 3‐yr history: (1) a single continuous GR crop; (2) a rotation of two GR crops; and (3) a GR crop rotated with a non‐GR crop. Weed species population density was surveyed in 20 0.5‐m2 plots per field four times each season from 2006 to 2010. Weed population density, species richness and diversity were analysed using repeated measures mixed models to test the effect of year, geographic location (based on plant hardiness zone) and weed management system (as described above). Weed community composition was analysed using NMDS ordination. The importance of geographic location, planted crop and weed management system were analysed using analysis of similarity and permutational ANOVA based on the Bray–Curtis similarity among sites calculated from the maximum weed species population density per site per year.ResultsA total of 329 weed species were identified across the six states and all time periods. Weed communities were most strongly correlated with geographic location and secondarily to the crop planted. Weed management system affected similarity among weed communities through an interaction with site location but not every year. The weed management systems of crop rotation and GR trait rotation generally reduced weed population density and species diversity, but the effect of crop rotation varied by geographic location.ConclusionsThe overall effects of weed management systems in fields including the GR trait on arable weed communities reinforce the need for locally adapted weed management programmes to steward the GR crop trait to manage for high weed diversity while reducing crop–weed competition and maximizing yield.

Віталітетна структура популяцій деяких видів бур’янів у посівах зернових культур

Досліджено особливості розвитку популяцій сегетальних видів (Cirsium arvense (L.) Scop., Sonchus arvensis L., Melandium album (Mill.) Garke, Setaria glauca (L.) Beauv., Fallopia convolvulus (L.) А. Lоve) у посівах зернових культур (пшениці озимої, жита, ячменю, гречки, гороху), які не оброблялися гербіцидами у господарствах лісостепової зони на території Сумської області.

Weed Populations as Affected by Residue Management Practices in a Wheat–Soybean Double-Crop Production System

Management practices and cropping systems that serve as integrated weed management practices, and at the same time can contribute to improved soil quality, will be important for the sustainability of agricultural production systems. The objective of this study was to assess weed species population density under contrasting tillage (conventional tillage [CT] and no tillage [NT]), residue burning (burn and no burn), and residue level (low and high) treatments after 5 and 6 yr of consistent management in a wheat–soybean double-crop production system. A field experiment was conducted from fall 2001 to fall 2007 in the Mississippi River Delta region of eastern Arkansas on a Calloway silt–loam. Weed assessments were conducted twice during the soybean growing season, before (early season) and after herbicide application (late season) in 2006 and 2007. Total weed density was greater under CT (513 plants m−2) than under NT (340 plants m−2) early in the growing season in 2006, but was greater under NT than CT late in the season in 2007, suggesting that the effectiveness of glyphosate on total weeds differs between CT and NT. Averaged across residue levels, grass species density was greatest in the NT–burn (68 to 167 plants m−2) combination and lowest in the NT–no-burn (41 to 63 plants m−2) early in the growing season in both years. Broadleaf density was greater early (200 to 349 plants m−2) than late (18 to 20 plants m−2) in the growing season under both CT and NT in 2006, but in 2007 broadleaf density did not differ by tillage treatment between seasons. Perennial weed density was greater in the burn (99 plants m−2) than in the no-burn (59 plants m−2) treatment in 2006. No tillage, no burning, and a high residue level appeared to contribute to the suppression of most weed species without reducing herbicide efficiency.

Modeling With Limited Data: The Influence of Crop Rotation and Management on Weed Communities and Crop Yield Loss

Theory and models of crop yield loss from weed competition have led to decision models to help growers choose cost-effective weed management. These models are available for multiple-species weed communities in a single season of several crops. Growers also rely on crop rotation for weed control, yet theory and models of weed population dynamics have not led to similar tools for planning of crop rotations for cost-effective weed management. Obstacles have been the complexity of modeling the dynamics of multiple populations of weed species compared to a single species and lack of data. We developed a method to use limited, readily observed data to simulate population dynamics and crop yield loss of multiple-species weed communities in response to crop rotation, tillage system, and specific weed management tactics. Our method is based on the general theory of density dependence of plant productivity and extensive use of rectangular hyperbolic equations for describing crop yield loss as a function of weed density. Only two density-independent parameters are required for each species to represent differences in seed bank mortality, emergence, and maximum seed production. One equation is used to model crop yield loss and density-dependent weed seed production as a function of crop and weed density, relative time of weed and crop emergence, and differences among species in competitive ability. The model has been parameterized for six crops and 15 weeds, and limited evaluation indicates predictions are accurate enough to highlight potential weed problems and solutions when comparing alternative crop rotations for a field. The model has been incorporated into a decision support tool for whole-farm management so growers in the Central Great Plains of the United States can compare alternative crop rotations and how their choice influences farm income, herbicide use, and control of weeds in their fields.

Selection of cereals for weed suppression in organic agriculture: a method based on cultivar sensitivity to weed growth

Cereal cultivars conferring a high degree of crop competitive ability, especially against aggressive weeds, are highly beneficial in organic farming as well as other farming systems that aim to limit the use of herbicides. In this study, thirteen winter wheat cultivars, plus one spring wheat and one winter oat were assessed for their competitive ability at key growth stages, across three seasons. The natural population of weed species was allowed develop without agronomic intervention. Weed suppression ability for each cultivar (S var) was calculated as the difference between weed growth in plots for each cultivar and the maximal weed growth (W max) from adjacent uncropped areas. The sensitivity of S var in response to changes in weed growth (S var W ) was derived from the linear regression coefficient of S var plotted against W max. There was significant variation in S var between cultivars and strong evidence for cultivars to vary in S var W . Amongst groups of cultivars with similar levels of S var some could be defined as being of higher or lower sensitivity to changes in weed growth. Some cultivars also had relatively good S var at high levels of weed growth. The use of both weed suppression ability and sensitivity across different levels of weed growth or weed populations has considerable potential for selecting new cultivars suitable for organic agriculture. Ideally new cultivars will be selected on the basis of high S var and/or low S var W . This analysis provides the means to measure sensitivity of cultivar performance across a range of favourable and unfavourable conditions.

Modelling land use strategies to optimise crop production and protection of ecologically important weed species

SummaryThere is a need to develop farming systems that enable both a satisfactory level of crop production and suitable environmental conditions for natural species. Wildlife‐friendly cropping techniques, such as a reduced amount of applied herbicide or a lower crop density, might be adopted in order to maintain populations of weed species of biological interest. An alternative might be to adopt an intensive cropping system in a part of the field and spare the other part as set‐aside or field margins, available for the natural development of plant species. The objective of this study was to present a method to compare two strategies for maintaining a desirable level of abundance of a given species of interest in agricultural areas, specifically (i) a strategy based on a wildlife‐friendly cropping system in a large cultivated area and (ii) a strategy based on a more intensive cropping system in a reduced area of cultivation, i.e. with land‐sparing. The principle is to calculate the ratio of crop production obtained with strategy (i) to the production obtained with strategy (ii) for a given target density of natural species. We show that the value of this ratio, and thus the relative performance of the two strategies, depends on the density of the weed species that can be maintained in an uncultivated ecological area. The method is applied in case studies of two plant species with contrasting ecology and conservation goals. The numerical results show that the strategy based on a wildlife‐friendly cropping system is more profitable in most situations.

The Ability of Barley to Compete with Weeds

The influence of crop plant density and variety on weed growth was studied in spring barley at a biodynamic and a conventional farm in two years. There was ample germination of weeds at both test sites. but the population of weed species was more diverse at the biodynamic farm.A reduction in barley plant density from normal to half or quarter density resulted in a 2-5 fold increase in shoot weed dry matter at harvest. The gain in grain yield obtained by herbicide treatment was 13.24 and 34%, respectively at normal, half, and quarter barley density. Normal plant density of barley was more important for the ability to compete with weeds than it was for obtaining a high grain yield.The amount of weed dry matter varied twofold between some of the barley varieties. This variation was not statistically significant within any of the experiments, but the reported high and low competitive ability of some of the varieties was confirmed. There were significant. Negative correlations between grain yield and weed dry matter in the individual varieties at the biodynamic farm. Generally a negative relation between grain yield level and weed growth was indicated by the experiments.