Predicting yield loss due to interference from two weed species using early observations of relative weed leaf area

Experiments were conducted on linseed ( Linum usiãissimum L.) and autumn-sown field bean ( Vicia faha L.) to test how well the relative leaf area-based yield loss prediction model of Kropff & Spitters could estimate yield loss due to interference from Stellaria media L. (common chick-weed) or barley ( Hordeum vulgare L.) alone or a combination of both S. media and barley . Damage coefficients were calculated for all comparisons. Generally, the model provided a better estimate of yield loss due to interference from barley than from S. media because of both the variability in crop yield response stemming from S. media's plasticity and the generally minor crop yield response to S. media interference. The addition to the model of a parameter accounting for asymptotic yield loss was, generally, not warranted for either S. media or barley in the single-weed species data sets. When both S. media and barley were present as weed species in the crop, the model that fitted the data best for six out of 10 data sets was the one in which a separate damage coefficient was included for both species. There was no evidence that the presence of S. media influenced damage coefficient values for barley. However, in the presence of barley a parameter accounting for asymptotic yield loss was warranted for S. media in the two-weed species model. The combination of the addition of this parameter and the presence or barley affected the values of the damage coefficients for S. media in the two-weed species compared with the single-weed species models. Consequently, it was shown for these two weed species that two-weed species yield loss prediction models parameterized using data from single-weed species experiments generally resulted in different estimates of yield loss in comparison with models parameterized using data from two-weed species experiments.     

Use of perennial cover crops to suppress weeds in Nicaraguan coffee orchards

Both uncontrolled weed growth and vegetation‐free orchard floors have been shown to affect coffee (Coflea arabica L.) negatively, but using cover crops as a solution has yielded conflicting results in different studies. In this study we tested the establishment success of three cover crop species under different management intensities and planting densities, as well as their long term weed‐controlling abilities and effects on weed community composition. Monthly manual weedings during the first 12 weeks after planting resulted in more rapid and extensive cover crop development compared with less intensive management. Transplanted Commelina diffusa Burm. f. grew most rapidly and controlled weeds by limiting light availability, but disappeared during the dry season and failed to establish at all on one of the farms. Arachis pintoi established and persisted for over 2 years, providing excellent weed control by outcompeting weeds for water and/or nutrient resources. Desmodium ovalifolium Wall required the longest time to establish and controlled weeds by an undetermined competitive mechanism. The sowing method of Desmodium led to intense intraspecific competition which probably decreased its effectiveness. Both Arachis and Desmodium led to lower relative abundances of grassy weeds and more perennial forbs, but total weed biomass was so low that these differences have no practical implications.     

A simple model of crop loss by weed competition from early observations on relative leaf area of the weeds

A new simple empirical model for early prediction of crop losses by weed competition was introduced. This model relates yield loss to relative leaf area of the weeds shortly after crop emergence using the relative damage coefficient q as the single model parameter. The model is derived from the hyperbolic yield density relationship and therefore accounts for the effects of weed density. It is shown that the model also accounts for the effect of different relative times of weed emergence. A strong advantage of the approach is that it can be used when weeds emerge in separate flushes. The regression model described experimental data on sugar-beet – lambsquarters (Beta vulgaris L. –Chenopodium album L.) and maize-barnyard grass (Zea mays L. –Echinochloa crus-galli L.) competition precisely. The model describes a single relationship between crop yield loss and relative leaf area of the weeds over a wide range of weed densities and relative times of weed emergence. Possibilities for scientific and practical application of the model are discussed.     

Prediction of the competitive effects of weeds on crop yields based on the relative leaf area of weeds

For implementation of simple yield loss models into threshold-based weed management systems, a thorough validation is needed over a great diversity of sites. Yield losses by competition wsth Sinapis alba L. (white mustard) as a model weed, were studied in 12 experiments in sugar beet (Beta vulgaris L.) and in 11 experiments in spring wheat (Triticum aestivum L.). Most data sets were heller described by a model based on the relative leaf area of the weed than by a hyperbolic model based on weed density. This leaf area model accounted for (part of) the effect of different emerging times of the S. alba whereas the density model did not. A parameter that allows the maximum yield loss to be smaller than 100% was mostly not needed to describe the effects of weed competition. The parameter that denotes the competitiveness of the weed species with respect to the crop decreased the later the relative leaf area of the mustard was determined. This decrease could be estimated from the differences in relative growth rate of the leaf area of crop and S. alba. However, the accuracy of this estimation was poor. The parameter value of the leaf area model varied considerably between sites and years. The results strongly suggest that the predictive ability of the leaf area model needs to be improved before it can be applied in weed management systems. Such improvement would require additional information about effects of abiotic factors on plant development and morphology and the definition of a time window for predictions with an acceptable level of error.     

Effect of weed position on yield loss in soyabean and a comparison between relative weed cover and other regression models

The importance of the position of weeds with respect to crop rows in the determination of crop yield-weed density relationships and the usefulness of relative cover (RC) of the weeds as an explanatory variable were studied in soyabean [Glycine max (L.) Merrill] competing with two summer weeds with contrasting canopy structure (Xanthium strumarium L. ssp. italicum and Echinochloa crus-galli L.). The position of the weeds was of little importance in the relationship between yield loss and weed density. This information is important because published experiments have used different types of weed distribution (e.g. evenly distributed or sown in rows). For both weed species it was possible to obtain a single relationship between yield loss and RC for measurements made from 30 days after crop emergence to soyabean canopy closure. The competitive effect of the weeds appeared to be strictly related to RC, indicating that for weeds growing taller than the crop the main competitive factor may be the shading caused by the leaves of the weeds situated above the crop canopy.     

Comparison of empirical models depicting density of Amaranthus retroflexus L. and relative leaf area as predictors of yield loss in maize (Zea mays L.)

The outcome of crop-weed competition should be predicted as early as possible in order to allow time for weed control measures. Maize grain yield losses caused by interference from Amaranthus retroflexus L. (redroot pigweed) were determined in 1991 and 1992. The performance of three empirical models of crop-weed competition were evaluated. Damage functions were calculated based on the weed density or relative leaf area of the weed. In the yield loss-weed density model, values of I (percentage yield loss at low weed density) were relatively stable for similar emergence dates of A. retroflexus across years and locations. Estimated maximum yield loss (A) was more variable between locations and may reflect environmental variation and its effect on crop-weed competition, at least in 1991. The two-parameter yield loss-relative leaf area model, based on m (maximum yield loss caused by weeds) and q (the relative damage coefficient) gave a better fit than the single-parameter version of the model (which includes only q). In both relative leaf area models, the values of q varied between years and locations. Attempts to stabilize the value of q by using the relative growth rate of the leaves of the crop and weed were successful; however, the practical application of such relative leaf area models may still be limited owing to the lack of a method to estimate leaf area index quickly and accurately.     

Assessment of competition between crops and weeds

A two-species model was used to summarize results of four experiments with two component mixtures of barley (Hordeum vulgare L.), peas (Pisum sativum L.), Chenopodium album L. and Sinapis alba L. grown in pots in greenhouses. The results, covering a wide range of plant densities both in mixtures and pure stands, showed that the model was not always able to describe the relationship between the yield of a species and the densities of itself and its companion species. The deviations from the model were in all instances greatest for the least competitive species. The model that quantifies competition and niche differentiation appeared to be too general because competition between species was not independent of the wide plant density ranges used here. The results are discussed in relation to possible improvements of the model and an analogy between the principles of assessing crop weed competition and the assessment of the relative potency of herbicides in bioassay studies is put forward.     

Multilayer feature fusion and attention-based network for crops and weeds segmentation

Journal of Plant Diseases and Protection - Distinguishing weeds from crops is a critical challenge in agriculture, with the existing agriculture semantic segmentation networks simply combining...     

Testing harrows for mechanical control of annual weeds in agricultural crops

Selectivity, defined as the ratio between weed control and crop burial in soil as a result of harrowing, has been used to test different implements according to their degree of selective operation. For this purpose a concept considering qualitative and quantitative aspects of selectivity has been proposed. This makes it possible to determine whether differences in selective mode of operation were caused by construction or by application of implements. Analysis of covariance was used to make this separation. Only if implements affected parameters in a model describing the relationship between crop soil cover and weed control were they suggested to operate with different selectivities. Crop soil cover was assessed by visual score as percentage of crop leaf area covered by soil as a result of harrowing. Using this method it was shown that none of the five harrows tested could be separated on the basis of their selective mode of operation. Selectivity was shown to be influenced by day of treatment, composition of the weed flora, site characteristics and degree of weed control. Harrowing at late crop growth stages was more selective than expected. Essai de hersage pour lutter mecaniquement contre les mauvaises herbes annuelles dans les cultures La sélectivité, définie comme le ratio entre la destruction des mauvaises herbes et l'en fouissement de la culture dans le sol après un hersage, a été utilisée pour tester différents matériels en regard de leur degré d'opération sélective. Pour cela, un concept prenant en compte les aspects qualitatifs et quantitatifs de la sélectivité a été proposé. Celui-ci permet de déterminer si les différences de sélectivité viennent de la construction ou de la mise en oeuvre des matériels. Une analyse de covar-iance a été utilisée pour opérer cette séparation. Seulement si les matériels affectaient les paramètres dans un modèle décrivant la relation entre la couverture de la culture par le sol et le deshérbage, il était envisagé d'opérer avec différentes sélectivités. La couverture de la culture par le sol a étéévaluée par une estimation visuelle du pourcentage de surface foliaire recouverte par le sol après un hersage. Par cette méthode il a été montré qu'aucun des 5 hersages testés ne pouvait être séparé sur la base de leur mode d'opération sélective. La sélectivité a été montrée comme étant influencée par le jour de traitement, la composition de la flore adventice, les caractéristiques du site et le taux de desherbage. Un hersage aux stades tardifs de la culture a été plus sélectif que ce que l'on attendait. Wirksamkeit verschiedener Eggen zur mechanischen Bekämpfung einjähriger Unkräuter in landwirtschaftlichen Kulturen Es wurden verschiedene Geräte nach ihrer selektiven Wirksamkeit beurteilt, wobei die Selektivität als Verhältnis zwischen der Bekämpfung der Unkräuter und dem Verschütten der Kulturpflanzen definiert wurde. Hierfür wurde ein Konzept vorgeschlagen, das die qualitativen und quantitativen Aspekte der Selektivität berücksichtigt. Dadurch konnte bestimmt werden, ob Selektivitätsunterschiede durch die Konstruktion oder durch die Anwendung eines Geräts bedingt waren. Die Unterscheidung erfolgte mittels Kovarianz Analyse. Nur wenn Geräte die Parameter eines Modells über die Beziehung zwischen dem Verschütten der Kulturpflanzen und der Unkrautbekämpfung beeinflußten, wurden ver-schiedene Selektivität angenommen. Das Verschutten der Kulturpflanzen wurde als prozentuale Bedeckung der Blattflächen mit Boden bonitiert. Danach ergab sich, daß die 5 getesteten Eggen in ihrer selektiven Wirkung nicht unterschieden werden konnten. Die Selektivitität wurde vom Tag der Behandlung, der Zusammensetzung der Unkrautflora, den Eigenschaften des Standorts und dem Grad der Unkrautbekämpfung beeinflußt. Das Eggen in fortgeschrittenen Entwicklungsstadien der Kulturpflanzen war selektiver als erwartet.     

Post-dispersal seed predation of non-target weeds in arable crops

Field experiments were conducted to quantify the natural levels of post-dispersal seed predation of arable weed species in spring barley and to identify the main groups of seed predators. Four arable weed species were investigated that were of high biodiversity value, yet of low to moderate competitive ability with the crop. These were Chenopodium album, Sinapis arvensis, Stellaria media and Polygonum aviculare. Exclusion treatments were used to allow selective access to dishes of seeds by different predator groups. Seed predation was highest early in the season, followed by a gradual decline in predation over the summer for all species. All species were taken by invertebrates. The activity of two phytophagous carabid genera showed significant correlations with seed predation levels. However, in general carabid activity was not related to seed predation and this is discussed in terms of the mainly polyphagous nature of many Carabid species that utilized the seed resource early in the season, but then switched to carnivory as prey populations increased. The potential relevance of post-dispersal seed predation to the development of weed management systems that maximize biological control through conservation and optimize herbicide use, is discussed.     

Dicotyledonous weeds of spring cereal crops in north-east Scotland

A survey of dicotyledonous weeds of spring cereals was conducted prior to herbicide application in 1985 in six districts of north-east Scotland, which involved a total of 113 fields. Results were similar to those from an earlier survey in 1973. The main species remained the same but in four of the six districts, total weed densities were lower. Stellaria media was the most common species except in Upper Banffshire and Morayshire where Galeopsis spp. and Polygonum aviculare, respectively, were predominant. The main changes apparent were a decline of Spergula arvensis and Polygonum persicaria, and an increase in Matricaria perforata and Viola arvensis in several districts.     

Assessment of yield loss caused by mycosphaerella blight in field pea crops in western Canada

Journal of Plant Diseases and Protection - The relationship between yield and disease severity of Mycosphaerella pinodes on field pea was analyzed and linear yield loss models were derived using...     

Experiments with isoproturon for the control of weeds in winter cereal crops

Isoproturon controlled Phalaris spp., Lolium spp., Avena sterilis L. and Papaver rhoeas L. in winter cereal crops, the dosages applied being in accordance with the different texture of the soils on which the herbicide was tested in the province of Toledo (Spain). The competitive effects of the weeds, particularly Avena sterilis were ascertained on a range of cereal parameters, not only those influencing yield, but also the grain weight/straw weight ratio. The influence of climatic and edaphic conditions on the efficiency of the herbicide was also investigated.     

防除大豆田阔叶杂草除草剂筛选试验报告

近年来 ,山东省大豆田应用较多的芽前除草剂以乙草胺为主 ,芽后除草剂有盖草能、禾草克、拿捕净等 ,这些除草剂对禾本科杂草有较好的防除效果 ,但都不能有效地控制铁苋菜、马齿苋、反枝苋等阔叶杂草的危害。因此 ,筛选适宜防除大豆田阔叶杂草的除草剂显得非常必要。我们于 1 999年进行了克莠灵、豆必乐、克阔乐、Ｃａｄｒｅ及豆草灭等除草剂对比试验。1　材料与方法1 .1　供试药剂供试药剂有 44%克莠灵水剂 (德国巴斯夫公司产 )、38%豆必乐水剂 (德国巴斯夫公司产 )、2 4%克阔乐乳油 (德国艾格夫公司产 )、2 4%Ｃａｄｒｅ水剂 (Ｉｍａｚｅｔ…     

Angular leaf spot of phaseolus beans: relationships between disease, healthy leaf area, and yield

ABSTRACT Five field experiments were conducted to investigate the relationship between the severity of visible disease (X), area under the disease progress curve (AUDPC), healthy leaf area index on any given day (HLAI), radiation intercepted by healthy leaf area on any given day (HRI), healthy leaf area duration (HAD), total healthy leaf area absorption (HAA), and yield of Phaseolus beans, cultivars Rosinha and Carioca, inoculated with Phaeoisariopsis griseola at several doses. In general, yield was not related to disease severity (X) or AUDPC. In contrast, the highest yields were always related to the highest values of HAD and HAA. The relationship between yield and HAD was linear in each of five trials (29.9 < R(2) < 70.2%, P < 0.001). The relationship between yield and HAA was linear in four of the trials (52.3 < R(2) < 70.3%, P < 0.001) and exponential in one of them (in which the plant canopy was the largest). Singlepoint models using HRI to estimate yield at various times during the crop season were developed. The slope of the yield-HRI relationship proved to be stable (26.8 +/-2.4 g MJ(-1)), regardless of cultivar, locale, planting date, and bean growth stage (from R5 to R8). The yield-HLAI relationship proved to be less consistent. HRI is proposed as a key explanatory variable for a transportable system of disease management; it may be useful in producing precise recommendations at the farm level.     

嘧草醚对双季稻田杂草的防效及后茬作物的安全性影响

为明确嘧草醚及其相关除草剂混用对移栽田杂草的防效及其对水稻和后茬作物的安全性,于2018年在江西双季稻田进行了田间试验。结果表明:10%嘧草醚WP对稗Echinochloa crus-galli有优异的防除效果,有效剂量45～120 g/hm~2处理药后45 d对早稻和晚稻田稗草的防效均在90%以上,且对水稻和后茬作物油菜、白菜、紫云英、小麦和马铃薯生长安全,但对阔叶类鸭舌草和莎草类异型莎草的防效较差;10%嘧草醚WP分别与10%苄嘧磺隆WP和25 g/L五氟磺草胺OD混用,对早稻和晚稻田稗草、鸭舌草和异型莎草的防效均达91%以上,且对水稻生长安全;而与扑草净混用对杂草的防效略低,且对水稻会产生药害,严重影响产量。因此,对于以稗草为优势种群的水稻田,可选用10%嘧草醚WP 45～60 g/hm~2进行防治;对于禾本科杂草、阔叶杂草和莎草科杂草发生并重的水稻田,可选择10%嘧草醚WP 30～45 g/hm~2与10%苄嘧磺隆WP或25 g/L五氟磺草胺OD 20～30 g/hm~2混用进行治理。     

Estimating relative crop yield loss resulting from herbicide damage using crop ground cover or rated stunting, with maize and sethoxydim as a case study

The research goal was to determine whether crop damage from herbicides measured early in the growing season soon after treatment could be used to estimate relative crop yield loss. Percentage stunting was rated visually and percentage crop ground cover (i.e. percentage of the ground surface covered by vegetation) was determined from video photographs taken 2–4 weeks after sethoxydim-susceptible maize ( Zea mays L.) was sprayed with sethoxydim at various rates plus crop oil concentrate. Averaged over 3 years, relative percentage maize yield was a negative sigmoidal function of relative sethoxydim rates from 0.065× to 0.5×, where the 1× rate was 420 g a.i. ha⁻¹ ( r ² = 0.80). Relative maize yield was positively linearly related to percentage crop ground cover and negatively linearly related to rated percentage stunting averaged over 3 years. Linear regression models of relative maize yield vs. percentage maize ground cover explained only slightly more data variability ( r ² = 0.86) than did rated stunting ( r ² = 0.82) over 3 years. The advantages and disadvantages of rated stunting and crop ground cover as scientific measurements are discussed.