Modelling population dynamics of Sinapis arvensis in organically grown spring wheat production systems

Although we know that alterations in crop density, crop spatial pattern and inclusion of more selective weed control can improve weed suppression for organic growers, it is unknown whether these result in changes to the weed seedbank that increase cropping system profitability over time. Data collected from field trials conducted in 2009 and 2010 in Maine, USA, comparing regional grower practices (Standard) with management that aimed to (i) facilitate better physical weed control through the use of wide row spacing and inter‐row cultivation (Wide) or (ii) enhance crop–weed competition through increased seeding rate and narrow inter‐row spacing (Narrow HD), were used to construct a matrix population model with an economic sub‐model. Using field measurements of grain yield and weed survival and fecundity, we investigated the lasting implications of employing alternative organic spring wheat (Triticum aestivum) production practices on Sinapis arvensis population dynamics. In most scenarios, the model indicated that regional production practices were not sufficient to prevent an increase in the weed seedbank, even with excellent weed control. The two alternative methods, on the other hand, were able to limit weed population growth when initial densities were low or cultivation efficacy was >80%. Due to higher seed costs in the Narrow HD system, net returns were still lower after 10 years of simulation in this system compared with wide rows with cultivation, despite a lower weed seedbank.     

Comparison of the uptake, movement and metabolism of fluroxypyr in Stellaria media and Viola arvensis

The uptake, movement and metabolism of fluroxypyr* is compared in two contrasting weed species, Stellaria media (susceptible) and Viola arvensis (moderately resistant). Similar rates of uptake occurred in both species, with a rapid cuticular uptake of 50% of that applied within 4 h. Total uptake by the underlying leaf tissue reached 66.6% and 70.8% in S. media and V. arvensis after 7 days. In translocation studies, in which ¹⁴C-fluroxypyr was applied to previously sprayed plants, 5.1% of applied ¹⁴C-activity was translocated from the treated leaves of S. media after 1 day, which increased to 42.2% after 7 days, recovered mainly from the stem tissue. In V. arvensis translocation was similar after 24 h however, after 7 days over 40% of applied ¹⁴C-activity remained in the treated leaves and only 9.7% was translocated, mainly to the developing leaves and apical tissue. ¹⁴C-activity extracted from the cuticle was the methylheptyl ester of fluroxypyr in both species. In the treated leaves and apical tissue, ¹⁴C-activity was the free acid of fluroxypyr and polar conjugates with a significantly greater proportion of the acid in S. media. It is concluded that the resistance or V. arvensis is partially due to reduced translocation and greater conjugation than in the susceptible S. media.     

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.     

The influence of nitrogen supply on the ability of wheat and potato to suppress Stellaria media growth and reproduction

Summary This paper tests the hypothesis that increased soil nitrogen supply reduces the growth of late-emerging weeds in wheat and potato by enhancing canopy leaf area development and thereby reducing the availability of light for weed growth. Two series of experiments were conducted: one in spring wheat (1997, 1999) with sown Stellaria media and one in potato (1998, 1999) with naturally emerged weeds, including S. media . For each crop, two cultivars were grown at three levels of nitrogen supply. In wheat, as in a monoculture of S. media , total dry weight and seed number of the weed increased with soil nitrogen supply, whereas in potato the opposite was found. Increased soil nitrogen supply increased the nitrogen uptake of S. media in wheat, despite the reduced light availability, indicating that S. media in wheat was limited by nitrogen. In potato, on the other hand, growth of S. media was limited by light availability, which decreased with increased soil nitrogen supply . We conclude that the differences in response of S. media in wheat and potato to additional nitrogen supply are attributable to the dual influence of soil nitrogen supply on light and nitrogen availability, which are mediated by the crops.     

Environmental maternal effects on seed morphology and germination in Sinapis arvensis (Cruciferae)

Pioneer plants are adapted to grow in unpredictable environments. These plants have evolved several traits related to seed morphology and germination to cope with this unpredictability. The main aim of this study was to investigate the effect of plant identity and maternal environment on seed mass and germination of Sinapis arvensis. This study was undertaken with S. arvensis plants grown in four experimentally manipulated resource availability scenarios: (i) nitrogen addition, (ii) water addition, (iii) nitrogen and water simultaneously added, and (iv) control. Plants grew under field conditions in an emerging plant community. Germination response was mainly affected by maternal plant identity. This reflects not only genotype quality but also phenotypic plasticity, which allows adaptation to habitat conditions. Seed coat colour together with mean seed mass per plant explained significant fractions of the variability in germination rate. Changes in the germination response because of maternal environmental effects were also detected. Germination rate decreased in seeds from nitrogen‐enriched conditions; this may be due to the induction of dormancy caused by high concentration of nitrogen in the seeds. Addition of water to maternal environment caused a decrease in total germination percentage and germination rate of seeds. Thus, our results provide evidence for maternal environmental effects on germination under field conditions. Furthermore, changes in germination timing, as detected in our study, may determine plant development and fitness in unpredictable conditions.     

Influence of soil moisture on the competitive ability and seed dormancy of Sinapis arvensis in spring wheat

Two experiments were carried out, one in 1995 and one in 1997, to investigate the competitive abilities of two spring wheat cultivars with Sinapis arvensis L. The spring wheat cultivars (Baldus and Canon) of contrasting growth habit were grown with and without S. arvensis under two different moisture regimes (10% and 70% of field capacity). In 1995, S. arvensis was found to be less competitive when subjected to moisture stress, resulting in smaller wheat yield losses in dry soil than in moist soil. In both years, seed production of S. arvensis was reduced by competition and moisture stress, and the seeds produced by plants that had been grown in drier soil were small and had negligible dormancy. Hence, in dry conditions, the competitiveness of S. arvensis and its potential to produce persistent seed may be reduced. Some differences between the two wheat cultivars were evident: cv. Baldus was more competitive against S. arvensis than cv. Canon. This could be attributed to differences in canopy structure.     

The influence of interspecific interference on the seed production of Stellaria media and Hordeum vulgare (volunteer barley)

The effects of the density and proportion of both volunteer barley ( Hordeum vulgare L.) and Stellaria media (L.) Vill. (common chickweed) on the seed yield of both species was investigated in linseed ( Linum usitatissimum L.) and autumn-sown field bean ( Vicia faba L.). A model was created to estimate these effects. It was a combination of two models. The first was a simple linear model relating weed seed number m² to weed dry weight m². The second was an inverse linear model relating weed dry weight per plant to weed density. A very good relationship existed between barley dry weight and number of seeds m² and between S. media dry weight and number of seed capsules m². This relationship was relatively consistent between experiments. The inverse linear model provided a good estimation of the relationship between weed density and weed dry weight per plant for both barley and S. media . Model variables, however, differed between experiments. Using the combined model it was estimated that, in the absence of other weed species and at a density of 800 plants m², S. media would produce between 4000 and 48 000 seeds m², whereas volunteer barley, at a density of 400 plants m², would produce between 2000 and 8000 seeds m². The presence of barley always reduced S. media seed yield and a barley population of 100 plants m² could reduce S. media seed yield by up to 79%. The presence of S. media reduced barley seed yield in only one of three experiments, in which a S. media density of 800 plants m² reduced barley seed yield by up to 68%. It was concluded that interspecific weed competition should not be ignored as a factor in models of weed population dynamics     

The effect of crop,cultivation and seed addition for birds on surface weed seed densities in arable crops during winter

Weed seeds present an agronomic threat, but are also an important food resource for wildlife in winter. Weed seed densities on the soil surface in winter were examined from 1999 to 2002 in 105 fields on three different farms in UK. The effect of the preceding crop, cultivation, position within the field and the application of seed for birds (bird seed) on surface seed abundance and species composition was tested. Six or fewer species comprised c. 80% of the weed seeds. By January of each study year, the densities of seeds important for farmland birds (key seeds) were 73% or 87% lower compared with early winter on two of the farms, but were stable on the third where seeds were incorporated through cultivation. At the edge and mid‐field, seed densities only exceeded 400 m^?2 in 17%, 10% and 12% of fields for total, key and dicotyledonous seeds respectively. The preceding crop only affected seed densities at one site; stubbles of winter barley had fewer seeds compared with winter wheat or spring barley. Seed densities varied between the edge and mid‐field, but trends were inconsistent between sites. The density of the larger seeds (Atriplex patula, Viola arvensis, Polygonum aviculare and Chenopodium album) were reduced in fields receiving bird seed. The objectives of weed control and conservation may not be mutually exclusive because seed return was most reduced where the ground remained uncultivated through the winter, yet this also provided the best foraging opportunities for surface feeding seed predators.     

Competition between sugarbeet and Sinapis arvensis and Chenopodium album, as affected by timing of nitrogen fertilization

The effects of timing of N fertilization (early, standard or late) on competition between two sugarbeet cultivars (Ritmo, semi-prostrate; and Rizor, erect) and two weeds ( Sinapis arvensis and Chenopodium album ) were studied over 2 years at Viterbo. In both years, time of N fertilization did not influence biomass, yield and yield quality of the weed-free crop, but early N fertilization gave higher crop biomass reduction in the presence of S. arvensis and lower crop biomass reduction in the presence of C. album . Root and sucrose yield responded to competition in the same way as biomass. However, percentage reductions were higher, as both weeds affected harvest index. The two cultivars showed the same response to competition. At the weed densities studied, crop competitive ability was favoured by late N fertilization in the presence of S. arvensis and by early N fertilization in the presence of C. album . Crop competition only reduced seed production by C. album but lowered seed germination of both weeds.     

The persistence of seeds of 16 weed species over six years in two arable fields

Summary Two experiments have investigated the persistence of 16 arable, annual broad-leaved weed species over 6 years in a silty loam and a clay soil. Small plastic beads were included as an 'inert' comparison. Seeds were broadcast in October on to plots at the start of the experiment, and these were either tine cultivated or ploughed annually thereafter. Plots were sown with either spring or winter wheat. As far as possible, weed seeding was prevented each year. For some species, the seed decline appeared to be slower on the ploughed plots than on the tined plots and in the winter wheat compared with the spring wheat. Seed decline also tended to be slower on the clay soil at Rothamsted than on the silty loam at Long Ashton. Some species declined rapidly (e.g. Brassica napus , Chrysanthemum segetum , Galium aparine , Galeopsis tetrahit ), with annual decline rates in excess of 58%, whereas others declined very little (e.g. Papaver rhoeas decline rate 9%). Most of the other species had decline rates between 20% and 40%. The results are discussed in relation to the development of population dynamics models to predict long-term consequences of alternative weed management strategies.     

转Bt基因作物对农田害鼠发生的影响分析*

转Bt基因作物的推广种植,正在改变着世界种植业格局。本文综述了实验室条件下转Bt基因作物对驯化鼠类影响的研究进展,结合近年来国内外农区鼠害的发生特征及其影响因素,分析了转Bt基因作物的推广种植对农田鼠类种群数量的潜在影响。     

Effects of depth of seed burial and soil aggregate size on seedling emergence of Alopecurus myosuroides, Galium aparine, Stellaria media and wheat

Seedling emergence of Alopecurus myosuroides Huds., Stellaria media L. (Vill.), Galium aparine L. and wheat (Triticum aestivum L.) was compared at a range of depths of soil cover from 2 to 11 cm. The covering soil was a fertile agricultural soil with 60% clay content which had been sieved into four aggregate sizes. The aggregate sizes used were 26-50 mm. 14-25 mm. 6-13 mm and below 6 mm. Total emergence of all species was reduced with increased depth of sou cover. With A. myosuroides and S. media, total emergence was lowest in fine soil conditions. Alopecurus myosuroides showed a marked interaction whereby response to depth of sowing was least with fine tilth. The time to 50% emergence showed a similar response. With all four species, seedling emergence was slowest at greater depths of sowing and with the finest tilth, the differences tending to increase with increasing depth of sowing. A vert high proportion of the time to 50% emergence was accounted for by the lag time between sowing and the first recorded emergence.     

Weed seed predation rate in cereals as a function of seed density and patch size,under high predation pressure by rodents

Weed seed predation is an ecosystem service, influencing weed population dynamics. The impact of weed seed predation on weed population dynamics depends on how predators respond to seed patches at the field scale. Seed predation will be most effective if the proportion of seeds predated increases with increasing size and seed density of patches. Density‐dependent rodent seed predation was measured by varying seed density and patch size in four irrigated conventionally managed cereal fields in north eastern Spain. Artificial weed seed patches were created by applying a range of Lolium multiflorum seed densities from 0 to 7500 seeds m^?2 in 225 m² patches (2008) or in patches that varied in size from 1 to 9 m² (2009). Seed predation was estimated using seed cards and seed frames. The granivorous rodents Mus spretus and Apodemus sylvaticus caused high seed predation rates (92%) in three fields, whereas in a fourth field, it was lower (47%). Rodents responded in an inversely density‐dependent manner, but this had little biological meaning as even in patches seeded with the highest density, the input to the soil seedbank was reduced by 88%. For the period of time this experiment lasted, hardly any new seeds would have entered the seedbank.     

广西旱地作物主要金龟子种类及其发生动态初步调查

2011-2013年, 通过挖土调查和太阳能诱虫灯系统调查了广西各地旱地作物金龟子的种类及其种群动态。统计结果表明, 全区共采集到金龟子4个科56种, 发生盛期为4月底至7月上旬; 各地发生种类和时期不同, 主要优势种为深绿异丽金龟、红脚异丽金龟、异丽金龟和桐黑异丽金龟, 发生盛期分别为5月下旬至7月中旬、6月中旬至8月上旬、5月中旬至6月中旬、5月中旬至6月下旬。     

Purple witchweed (Striga hermonthica) germination and seedbank depletion under different crops,fallow, and bare soil

Seedbank density is an important aspect that determines the amount of damage that the parasitic weed, purple witchweed (Striga hermonthica; hereafter, called “Striga”), causes on its crop hosts. The seedbank depletion of Striga was measured in Mali and Niger during the 2004 rainy season under the host crops, pearl millet and sorghum, the non‐host crops, cowpea and sesame, the intercrops of pearl millet or sorghum with cowpea or sesame, and fallow with or without weeding. Two methods were used and compared; namely, a seed bag method and a soil‐sampling method. The fate of the seeds was assessed by a seed press test. Seed germination, as determined by the presence of empty seed coats, contributed most to the seedbank depletion of Striga under a variety of crop covers and fallow. The highest seedbank depletion was found under the monocultures of the host crops. The intercrops of the host and non‐host crops caused less seedbank depletion, followed by the monocultures of the non‐host crops, fallow, and bare soil. The seed bag method and the soil‐sampling method yielded similar percentages of seedbank depletion, while the former allowed for distinguishing between the germinated and diseased seeds. The results suggest that, although all the tested crop species can cause the seed germination and seedbank depletion of Striga, management by using host cereal crops causes the highest amount of germination and has the highest potential to deplete the soil seed bank, provided that seed production is prevented.     

Weed seed movement and dispersal strategies in the agricultural environment

This paper reviews the current knowledge on weed seed movement in an agricultural environment. Seed movement is analyzed both from an agronomic and ecological perspective, focusing predominantly on horizontal seed movement. Abiotic (anemochory and hydrochory), as well as biotic (autochory, myrmecochory, epizoochory, and endozoochory) weed seed dispersal typologies are examined, highlighting the mechanisms involved, the specializations displayed by weed species that have evolved by exploiting a particular dispersal mechanism, and their adaptive interaction with the surrounding ecosystem. Emphasis is also placed on the crucial role of human activity (anthropochory), which can affect natural (biotic and abiotic) weed seed dispersal at several stages, partly via the worldwide commercial seed trade but, above all, by crop management operations, thereby potentially facilitating the entry and spread of alien weed species. This phenomenon, together with the invasive expansion of existing weeds that more successfully coevolve and adapt to the new environment, might exert an adverse effect on biodiversity. In-depth knowledge of weed seed dispersal, survival, and germination mechanisms is therefore essential for effective and eco-compatible management of the weed phytocoenoses present in the agroecosystem in order to promote a rational trade-off between agricultural productivity and environmental protection.     

云南核桃主产区天牛种类及种群动态

以云南主栽核桃品种漾濞泡核桃林为研究对象, 使用4种引诱剂诱捕天牛, 实地调查天牛发生种类及种群消长动态, 结果表明:漾濞泡核桃林发生的天牛种类有3亚科7属11种, 它们分别是幽天牛亚科的梗天牛属, 天牛亚科的闪光天牛属和绿虎天牛属, 沟胫天牛亚科的墨天牛属、梯天牛属、星天牛属和瘤象天牛属, 其中以墨天牛属的松墨天牛、梗天牛属的赤梗天牛、梯天牛属的橄榄梯天牛、瘤象天牛属的麻点瘤象天牛数量居多, 分别占诱捕总量的65.77%、15.32%、7.21%和2.70%。首次发现闪光天牛属的中华闪光天牛对核桃有较严重为害。对核桃有为害的天牛共有7种, 分别是:绿虎天牛属的绿毛绿虎天牛、梯天牛属的粗角梯天牛、星天牛属的星天牛和蓝斑星天牛、瘤象天牛属的灰背瘤象天牛和麻点瘤象天牛、闪光天牛属的中华闪光天牛。试验区天牛成虫的活动期集中发生在5月-7月。该研究为云南漾濞泡核桃林天牛的科学监测和及时防治提供了理论依据和指导。     

Variations in the resistance of Stellaria media to mecoprop due to biotype, application method and 1-aminobenzotriazole

An investigation was made into the resistance of some biotypes of Stellaria media to mecoprop. Comparison of the sensitivity of five biotypes to foliar applications of mecoprop salt confirmed the presence of resistant and sensitive types and one of intermediate sensitivity. Applications of mecoprop through the roots of plants growing in nutrient culture were also more active on biotypes sensitive to foliar mecoprop, although the differences were less marked than they were with foliar treatments. Thus, possible differ ences in retention, uptake and translocation do not seem to be important causes of resistance. Consequently, it appears that resistance is associated with detoxification of mecoprop at the site of action. In two further experiments the cytochrome P450 mixed function oxidase inhibitor, 1-aminobenzotdazole, had only a small effect on the susceptibility of resistant S. media plants to mecoprop. The importance of these data in the elucidation of the mechanism of resistance is discussed.