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1.
A simple model of crop loss by weed competition from early observations on relative leaf area of the weeds 总被引：8，自引：1，他引：8
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. 相似文献
2.
S Fahad S Hussain S Saud S Hassan H Muhammad D Shan C Chen C Wu D Xiong S B Khan A Jan K Cui J Huang 《Weed Research》2014,54(5):475-483
Echinochloa colona and Trianthema portulacastrum are weeds of maize that cause significant yield losses in the Indo‐Gangetic Plains. Field experiments were conducted in 2009 and 2010 to determine the influence of row spacing (15, 25 and 35 cm) and emergence time of E. colona and T. portulacastrum (0, 15, 25, 35, 45 and 55 days after maize emergence; DAME) on weed growth and productivity of maize. A season‐long weed‐free treatment and a weedy control were also used to estimate maize yield and weed seed production. Crop row spacing as well as weed emergence time had a significant influence on plant height, shoot biomass and seed production of both weed species and grain yield of maize in both years. Delay in emergence of weeds resulted in less plant height, shoot biomass and seed production. However, increase in productivity of maize was observed by delay in weed emergence. Likewise, growth of both weed species was less in narrow row spacing (15 cm) of maize, as compared with wider rows (25 and 35 cm). Maximum seed production of both weeds was observed in weedy control plots, where there was no competition with maize crop and weeds were in rows 35 cm apart. Nevertheless, maximum plant height, shoot biomass and seed production of both weed species were observed in 35 cm rows, when weeds emerged simultaneously with maize. Both weed species produced only 3–5 seeds per plant, when they were emerged at 55 DAME in crop rows spaced at 15 cm. Infestation of both weeds at every stage of crop led to significant crop yield loss in maize. Our results suggested that narrow row spacing and delay in weed emergence led to reduced weed growth and seed production and enhanced maize grain yield and therefore could be significant constituents of integrated weed management strategies in maize. 相似文献
3.
The expansion of atrazine‐resistant Chenopodium album (common lambsquarters) since the 1980s has forced New Zealand's maize‐growers to use an additional postemergence herbicide application. The frequent use of dicamba for this has selected for a common lambsquarters population with reduced sensitivity to dicamba. Initial greenhouse experiments with seeds that had been collected from the plants that survived field applications of dicamba showed that these plants could tolerate ≤1.2 kg ha?1, fourfold the recommended rate. These dicamba‐resistant plants were morphologically distinct from the susceptible population. The leaves of the resistant plants were less dentate and a lighter shade of green. The resistant plants were shorter, had a lower biomass and growth rate and flowered ≤19 days earlier than the susceptible plants. When grown together in various density ratios, the average biomass of both the susceptible and the resistant plants increased as the number of susceptible plants decreased in the mixture. The field experiments demonstrated that the resistant population tolerated dicamba at ≤2.4 kg ha?1, eightfold the recommended rate. Postemergence applications of bromoxynil, pyridate, nicosulfuron and mesotrione effectively controlled both populations. Nicosulfuron and mesotrione provided long‐term residual control, with nicosulfuron being more effective on the grass weeds. High rates of dicamba damaged the maize plants, resulting in an increased weed cover and reduced grain yield. The number of viable common lambsquarters seeds in the soil seed bank at the end of the growing season declined in the treatments in which common lambsquarters was controlled effectively. 相似文献
4.
Influence of sowing density and spatial pattern of spring wheat (Triticum aestivum) on the suppression of different weed species 总被引：1，自引：0，他引：1
To better understand the potential for improving weed management in cereal crops with increased crop density and spatial uniformity, we conducted field experiments over two years with spring wheat ( Triticum aestivum ) and four weed species: lambsquarters ( Chenopodium album ) , Italian ryegrass ( Lolium multiflorum ), white mustard ( Sinapis alba ), and chickweed ( Stellaria media ). The crops were sown at three densities (204, 449, and 721 seeds m−2 ) and in two spatial patterns (normal rows and a highly uniform pattern), and the weeds were sown in a random pattern at a high density. In most cases, the sown weeds dominated the weed community but, in other cases, naturally occurring weeds were also important. There were strong and significant effects regarding the weed species sown, the crop density, and the spatial distribution on the weed biomass in both years. The weed biomass decreased with increased crop density in 29 out of 30 cases. On average, the weed biomass was lower and the grain yield was higher in the uniform compared to the row pattern in both 2001 and 2002. Despite the differences in weed biomass, the responses of L. multiflorum , S. media , and C. album populations to crop density and spatial uniformity were very similar, as were their effects on the grain yield. Sinapis alba was by far the strongest competitor and it responded somewhat differently. Our results suggest that a combination of increased crop density and a more uniform spatial pattern can contribute to a reduction in weed biomass and yield loss, but the effects are smaller if the weeds are taller than the crop when crop–weed competition becomes intense. 相似文献
5.
BAHRAM MIRSHEKARI AZIZ JAVANSHIR HAMDOLLAH KAZEMI ARBAT 《Weed Biology and Management》2010,10(2):120-125
Weeds that emerge along with or immediately after crop plants usually can reduce the yield of those crops. Two randomized complete block design experiments were conducted during 2006 and 2007 in Tabriz, Iran to determine the critical period of redroot pigweed control in the green bean hybrid “Cantander”. The treatments were weed‐infested and weed‐free plots at 2, 4, 6, 8, 10, and 14 weeks after bean emergence (WABE). The green bean biomass was affected by the early emergence of redroot pigweed, but it was not reduced when redroot pigweed emerged at 10 weeks after crop emergence, along with crop emergence, and grew with green bean until 4 WABE. The redroot pigweed biomass decreased by 2.7 g m?2 per day when weed emergence was delayed. Each 100 g m?2 of weed biomass that was produced resulted in a 1.4 kg ha?1 loss in the green bean yield. When redroot pigweed interference lasted for ≥4 weeks after green bean emergence, the green bean yield was reduced significantly. Weeds, which emerged 2 weeks after green bean and thereafter were controlled, did not decrease crop productivity significantly. The highest crop yield was obtained when the weed emerged at 14 WABE. The critical period of redroot pigweed control, considering a 10% yield loss, was between 19 and 55 days after green bean emergence. Thus, weed control practises should be begun no later than 3 WABE and should continue until at least 8 WABE in order to obtain the maximum green bean yield. 相似文献
6.
7.
Critical periods of weed competition in cotton in Greece 总被引：1，自引：0，他引：1
D. Papamichail I. Eleftherohorinos R. Froud-Williams F. Gravanis 《Phytoparasitica》2002,30(1):105-111
Four experiments were conducted in central Greece during 1997 and 1998 to determine the late-season presence of weeds in cotton
(Gossypium hirsutum L.) and the critical times for removing weeds. Experiments were conducted in natural, heavily infested cropland. The presence
of weeds for more than 3 weeks after crop emergence caused significant reductions in crop growth and lint yields. However,
weeds that emerged 11 weeks or more after crop emergence did not adversely impact yields. Total weed biomass increased with
increasing time prior to weed removal. A weed-free period of 11 weeks after crop emergence was needed to prevent significant
reductions in cotton height, biomass, number of squares, and yield. These results indicated that postemergence herbicides
or other control measures should be initiated within 2 weeks after crop emergence to avoid significant yield reduction. For
greater efficiency, soil-applied herbicides in cotton should provide effective weed control for at least 11 weeks. Curvilinear
regression equations were derived to describe the relationship between critical periods of weed presence and cotton growth
and fruit development. 相似文献
8.
Five fodder crop systems of different intensity (ranging from a double annual crop of Italian ryegrass + silage maize to a permanent meadow) were adopted for 30 years in the lowlands of Northern Italy under two input levels, differing mainly in their provision of organic fertiliser (manure). Herbicides were used in the maize crops included in all systems, except the meadow. After 30 years, the weed seedbank of all systems and input levels were assessed by the seedling emergence technique on soil samples from each plot. The cropping systems determined the abundance and composition of the weed assembly. Relatively few, frequent species made up the majority of the emerged seedlings in all systems, and there was no relationship between the total number of emerged seedlings and the mean number of species recorded in the different systems. Arabidopsis thaliana and Oxalis corniculata were abundant in the annual double crop and in the 3- and 6-year rotations that also comprised the annual double crop. These weeds, however, were unlikely to represent a major threat to the crops, due to their vigour and growth period. The permanent meadow tended to greater weed biodiversity than the other systems. The application of manure favoured the seedbank of species such as Lolium multiflorum, Digitaria sanguinalis and A. thaliana. Weed communities in the different systems were mainly determined by herbicide application, (through the ability of weeds to avoid its effects, determined by the weed life history and emergence period) and manure application (with its possible dual effect of spreading weed seeds and favouring nitrogen-responsive weeds). 相似文献
9.
A. FERRERO 《Weed Research》1996,36(2):197-201
In field studies carried out in 1992 and 1993, several durations of growth of Heteranthera reniformis Ruitz et Pavon were established in flooded rice (Oryza sativa L.) to evaluate weed influence on crop yield using day-degree predictive models for weed growth. H. reniformis was allowed to emerge at 7-day intervals from rice emergence until 49 days later. Weeds that emerged with the rice accumulated 403 day-degrees during the first 49 days. Weeds allowed to utilize 308 day-degrees had a dry weight reduction of 20% compared with plants that emerged with the rice. With the loss of all 403 day-degrees dry weight was reduced by about 95%. Maximum leaf area index (LAI) was 2.8, reached at 308 day-degrees. Weed density ranged from 48 to 5 plants m-2 when all 403 day-degrees were accumulated or lost by the plant respectively. When the weed lost only 95 day-degrees out of the possible 403 (1 week's delay in emergence) rice yield was 34% and 39% lower in 1992 and 1993 respectively. When the weed was allowed to accumulate ail 403 day-degrees yield reduction reached 62% in 1992 and 68% in 1993, very similar to the control plot, which were maintained weedy throughout (64% and 70.5%). After an accumulation of 403 day-degrees the weed reduced the number of rice panicles by 45% in 1992 and 38% in 1993. 相似文献
10.
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. 相似文献
11.
PHILLIP T. FUJIYOSHI STEPHEN R. GLIESSMAN JEAN H. LANGENHEIM 《Weed Biology and Management》2007,7(2):105-114
In order to examine the weed-suppressive properties of squash interplanted in corn, we compared different planting densities and weeding regimens, measuring the weed biomass, light interception by crop canopy, and yield. The corn was machine-planted at a normal monocrop density, while the squash was hand-planted at or above a normal monocrop density in an irrigated and otherwise mechanized system. A simulated intercrop consisting of corn with an artificial squash canopy was included. Interplanted squash reduced the biomass of the total weeds and of the dominant weeds, Amaranthus retroflexus and Convolvulus arvensis . The corn yield was not necessarily reduced in the intercrop, except at a higher squash density or under limited moisture. Shading by the squash was the major mechanism of weed suppression, but the analysis suggested that other factors, such as allelopathy, might contribute. Additional hand weeding had no effect on the corn yield. 相似文献
12.
H. M. LAWSON 《Weed Research》1983,23(1):27-38
Competition between annual weeds and vining peas (Pisum sativum L.) at five target population densities between 11 and 194 plants/m2 was examined by means of periodic destructive sampling of weedy and weed-free plots. A further area of each plot was cut and vined to assess yields. Weeds impaired vegetative development, particularly by reducing tillering in low density crops. This resulted in weedy plots having fewer pods per plant at harvest but a lower proportion of flat pods than weed-free plots. Weeds had no effect on numbers or weights of peas in full pods nor on tenderometer values of samples of vined peas. Adverse effects of weeds on the growth of individual crop plants decreased with increasing crop density. However, at lower crop densities many of the additional pods on weed-free plots contributed little to vined yield, while at higher densities, direct or indirect effects of weeds increased the problem of maintaining sufficient photosynthetic area during pod swelling to prevent pod abscission and poor ovule development. Regression analysis of yield on crop density and of yield on numbers of pods per plant showed that vined yield per hectare was reduced by weeds by a constant amount across the range of densities and numbers of pods examined. Vining throughput was also reduced in weedy as compared with weed-free crops, even on high density plots where little or no weed vegetation remained at harvest. In general, weed presence had effects similar to those caused by increasing crop density, but without the additional contribution to yield made by extra plants. Higher density crops suppressed weeds very effectively but were no less vulnerable to yield loss than those of lower density; they therefore merit just as much attention to effective weed control as crops suffering more visibly from competition by weeds. 相似文献
13.
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. 相似文献
14.
HANWEN WU STEVEN R. WALKER VIKKI A. OSTEN GEOFF ROBINSON 《Weed Biology and Management》2010,10(3):185-193
Field studies were conducted at two locations in southern Queensland, Australia during the 2003–2004 and 2004–2005 growing seasons to determine the differential competitiveness of sorghum (Sorghum bicolor L. Moench) cultivars and crop densities against weeds and the sorghum yield loss due to weeds. Weed competition was investigated by growing sorghum in the presence or absence of a model grass weed, Japanese millet (Echinochloa esculenta). The correlation analyses showed that the early growth traits (height, shoot biomass, and daily growth rate of the shoot biomass) of sorghum adversely affected the height, biomass, and seed production of millet, as measured at maturity. “MR Goldrush” and “Bonus MR” were the most competitive cultivars, resulting in reduced weed biomass, weed density, and weed seed production. The density of sorghum also had a significant effect on the crop's ability to compete with millet. When compared to the density of 4.5 plants per m2, sorghum that was planted at 7.5 plants per m2 suppressed the density, biomass, and seed production of millet by 22%, 27% and 38%, respectively. Millet caused a significant yield loss in comparison with the weed‐free plots. The combined weed‐suppressive effects of the competitive cultivars, such as MR Goldrush, and high crop densities minimized the yield losses from the weeds. These results indicate that sorghum competition against grass weeds can be improved by choosing competitive cultivars and by using a high crop density of >7.5 plants per m2. These non‐chemical options should be included in an integrated weed management program for better weed management, particularly where the control options are limited by the evolution of herbicide resistance. 相似文献
15.
The dynamics of Sorghum halepense tiller emergence and rhizome biomass were studied in field experiments. The effect of different application dates of a post-emergence herbicide on crop yield was measured. The relationship between accumulated thermal units (A.T.U.) and the percentage of emerged tillers in soybean was described by a single non-linear regression model, independent of initial bud density. The estimates of population density were generally higher than those predicted by the original model developed by Satorre, Ghersa & Pataro (1985). In the absence of a crop, the higher the density of the weed the more concentrated the tiller emergence in the early part of the tillering period. The rhizome biomass reached a minimum value at about 230°C days, and was independent of the initial weed density. The maximum herbicide efficiency was achieved when the application was performed closest to the period of minimum rhizome biomass. The results show the feasibility of optimizing S. halepense control by calculating the period f minimum rhizome biomass. Such a criterion ls consistent with the maximization of crop yields. 相似文献
16.
Modelling the effects of weeds on crop production 总被引：3，自引：0，他引：3
M. J. KROPFF 《Weed Research》1988,28(6):465-471
In most quantitative studies on interplant competition, static regression models are used to describe experimental data. However, the generality of these models is limited. More mechanistic models for interplant competition, which simulate growth and production of species in mixtures on the basis of the underlying physiological processes, have been developed in the past decade. Recently, simulation models for competition between species for light and water were improved and a detailed version was developed for sugarbeet and fat hen (Chenopodium album L.). The model was validated with data sets of five field experiments, in which the effect of fat hen on sugarbeet production was analysed. About 98% of the variation in yield loss between the experiments (which ranged from –6 to 96%) could be explained with the model. Further analysis with the model showed that the period between crop and weed emergence was the main factor causing differences in yield loss between the experiments. Sensitivity analysis showed a strong interaction between the effect of the variables weed density and the period between crop and weed emergence on yield reduction. Different quantitative approaches to crop-weed competition are discussed in view of their practical applicability. Simulations of experiments, where both the weed density and the period between crop and weed emergence were varied over a wide range, showed a close relation between relative leaf cover of the weeds shortly after crop emergence and yield loss. This relation indicates that relative leaf cover of the weeds accounts for both the effect of weed density and the period between crop and weed emergence. This relation has the potential to be developed into a powerful tool for weed-control advisory systems. 相似文献
17.
The performance of three empirical models describing white bean yield loss (YL) from common ragweed competition was compared using field experiments from Staffa and Woodstock, both in Ontario, Canada, in 1991 and 1992. One model was based upon both weed density and relative time of emergence. The other two models described yield loss as a function of weed leaf area relative to the crop. The model based on both weed density and relative time of emergence best described the data sets. The predicted maximum yield loss (A) and the parameter for relative time of weed emergence (C) varied across locations and years whereas the yield loss at low weed density (I) was relatively more consistent across locations and years. Use of thermal time (base temperature=10oC) rather than calendar days did not change the overall fit of the model, but reduced the value of the parameter for the relative time of weed emergence (C). The two parameter leaf area model accounting for maximum yield loss (m) gave a better fit to the data compared with the one parameter model. The relative damage coefficient (q) varied with time of leaf area assessment, location and year. Values of q calculated from relative leaf area growth rates of the crop and weed were similar to observed values. The relationship between q and accumulated thermal time was linear but varied with location and year. As management tools, models based upon relative leaf area have advantages over models based on density and relative time of emergence since the level of weed infestation needs only to be assessed once, whereas density and emergence time require frequent observations. The ability to assess accurately and quickly both the crop and weed leaf area, however, may limit the practical application of models based on leaf area. The inability of empirical models to account for year–to–year variation in environmental conditions was observed. 相似文献
18.
1997—1999年在山东省桓台县的田间试验表明，荠菜 播娘蒿杂草群落有两个萌发出苗高峰期，除草临界期为小麦苗后的125-175天。杂草发生密度(株／m^2)与冬小麦产量(kg／hm^2)、有效穗数(万穗／hm^2)及秸秆生物量(kg/hm^2)的最佳模型均为直线函数关系，方程分别为Y3=-5．4545X 5995．5，Y4=-0．0293X 31．098和Y5=-8．329X 6987．1。使用巨星除草的经济防除阈值为20株／m^2，人工除草的经济防除阈值为70株／m^2。考虑到杂草群落的生长动态，本区秋季用巨星防除的最低密度为12株／m^2，并认为可以用步测法来粗略测定田间杂草防除密度。 相似文献
19.
Leandro Galon Felipe A. De David César T. Forte Francisco W.R. Júnior André L. Radunz Renato Kujawinski Lauri L. Radunz Camile T. Castoldi Gismael F. Perin Altemir J. Mossi 《Weed Biology and Management》2018,18(1):26-40
Corn stands out among the cultivars because of its high importance in food, animal feed and raw materials for energy production. The quantity and quality of the harvested grain can be reduced, mainly due to inadequate weed management. Nowadays, weed control is accomplished with the use of herbicides as pre‐emergence and postemergence, applied alone or in a tank mix. This study aimed to evaluate the efficiency of the control of weeds and phytotoxicity of the herbicides that were applied in tank mix or isolated in the corn hybrids, Formula TL® and SYN 7B28 . Two experiments were conducted: in the 2012/2013 season (Formula TL®) and 2013/2014 season (SYN 7B28). There was a low initial phytotoxicity of all the tested herbicides in the initial evaluation; however, from 14 days after treatment, it was minimal. The weed control of Ipomoea indivisa, Urochloa plantaginea and Euphorbia heterophylla in both experiments was better, in general, when using the tank mixtures of atrazine + simazine + tembotrione and atrazine + simazine + mesotrione, respectively. The application of atrazine + simazine + tembotrione in the SYN 7B28 hybrids provided, with the exception of the thousand‐grain weight, the best expression of grain yield components, combining a low phytotoxicity and best control of the weeds. The Formula TL® hybrid presented the highest mass of a thousand grains and yield with the application of nicosulfuron + tembotrione. The yield average difference of the herbicide treatments and the unweeded control showed an increase of 27.66 and 34.59% in the grain yield of the corn hybrids, Formula TL® and SYN 7B28, respectively. 相似文献
20.
SAYYED F. SABERALI MOHAMMAD A. BAGHESTANI ESKANDAR ZAND 《Weed Biology and Management》2008,8(1):54-63
Crop density and spatial arrangement affect the potential of intraspecific and interspecific competition as they increase the canopy light absorption. The effects of the corn density and planting pattern on the growth of common lambsquarters ( Chenopodium album L.) was studied in a randomized, complete block design with three replications and factorial arrangement at University College, Aburaihan, Iran, in 2003. The plant density was the recommended density and 1.5-fold the recommended density. The planting pattern treatment also was performed at two levels: one- and two-row planting. The common lambsquarters density was 0, 5, 10, and 15 plants m−1 per row. The results showed that the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters were decreased by increasing the corn density. But, the leaf area index, biomass production, crop growth rate, and inflorescence biomass of the dry matter of common lambsquarters under the two-row planting pattern were less than under the one-row planting pattern, although these differences were not significant. 相似文献