Mechanical and cultural strategies to control Cirsium arvense in organic arable cropping systems

Infestation with Cirsium arvense in organic cropping is an increasing problem in many parts of Europe. Non‐chemical management strategies against C. arvense, based on cultivation tactics and/or different cutting regimes, have received very little attention for many years. This study presents results from four experiments, undertaken under organic growing conditions, on the effects of repeated mowing or hoeing during the first part of the growing season, used in combination with competition from a suppressive crop (grass/white clover mixture or red clover). The strategies were mainly aimed at diminishing the regenerative capacity of C. arvense and the effects were thus measured in the subsequent year in spring barley crops, in the absence of any weed control. In general, number of passes of mowing and hoeing linearly reduced the amount of aboveground C. arvense biomass in the subsequent year. Increased competition induced by the competitive crops further reduced C. arvense biomass. Differences in barley yield were explained by the amount of C. arvense biomass only in one experiment, where this weed was most abundant. Our results suggest that an acceptable level of C. arvense control can be achieved through an intensive hoeing or mowing campaign, within one growing season only. This may lead to increased crop yield in the subsequent year.     

Effects of selective cutting and timing of herbicide application on growth and development of Cirsium arvense in spring barley

Recently, a new implement for controlling weeds in cereals (CombCut) has been developed. It cuts weeds in growing cereals without damaging them by using the physical differences (in height, stem thickness, straw stiffness and branching pattern) between crops and weeds. To evaluate and compare the effects of selective cutting with different timings of herbicide application on Cirsium arvense in spring barley, a randomised block experiment was conducted in Sweden in 2015–2017, in a field with a naturally occurring C. arvense population. Treatments consisted of control (C), herbicide application at 4–5‐leaf stage of C. arvense (H1), herbicide application at 8–10‐leaf stage (H2) and selective cutting at 10‐leaf stage (S). The treatments were performed in 2015 and repeated in 2016 in the same plots, and a final evaluation was performed in 2017. Compared to the control, S, H1 and H2 were equally efficient in reducing above‐ground biomass production of C. arvense and increasing spring barley grain yield per unit area. The number of C. arvense shoots per area was, however, higher in S compared to H1 and H2. No differences in control effects on shoot number were observed between H1 and H2. Our study indicates that (i) selective cutting (S) reduces C. arvense equally efficient as herbicide application and (ii) early herbicide spraying is as efficient as spraying later in the season.     

Influence of intra-row cruciferous surrogate weed growth on crop yield in organic spring cereals

In Northern Europe, inter-row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed-free inter-row zone. However, hoeing has a lesser effect on weeds growing in the intra-row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall-growing, competitive, cruciferous weeds in the intra-row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra-row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH₄-N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra-row plants/m² of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra-row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra-row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra-row weeds and limit crop losses.     

Assessment of the compensation point of Cirsium arvense and effects of competition,root weight and burial depth on below‐ground dry weight – leaf stage trajectories

Farmers are recommended to employ mechanical control when Cirsium arvense is most sensitive to disturbance. Earlier studies suggest that this occurs at a stage of minimum below‐ground dry weight, coinciding with three to seven or seven to ten leaves per shoot, depending on the definition of below‐ground dry weight. However, some farmers notice better effects when mechanical control is performed at earlier leaf stages. To estimate the compensation point (CP), defined as the minimum weight of the entire below‐ground structure of C. arvense and to further understand links between initial root weight, planting depth and crop competition, three outdoor pot experiments were performed in Sweden in 2013‐2014. We hypothesised that (i) CP likely occurs before C. arvense has developed three leaves, (ii) relative depletion of the below‐ground system at CP is less at lower initial root weight compared with higher weight, and (iii) methodological variations in CP estimations have minor impact on the results. We found that the CP for C. arvense in all treatments occurred before shoots had developed three leaves and that treatment effects were minor (<0.5 leaf stages). Leaf and leaf stage definitions, choice of leaf range and model also had minor effects on CP estimates. Depletion of planted root fragments ceased around leaf stages 3‐4, and their partial replenishment also constitutes evidence for a CP at early leaf stages. For agronomy, our results imply that mechanical control of C. arvense should be performed earlier than previously recommended, probably before reaching an average of three to four leaves per shoot.     

Cirsium arvense (L.) Scop. competition with winter wheat (Triticum aestivum L.)

A series of field experiments was conducted to evaluate the competitive effect of Cirsium arvense (L.) Scop. on winter wheat (Triticum aestivum L. ‘Norstar’) yield. Grain yield at the centre of dense C. arvense patches ranged from 28–71% of the yield in adjacent weed-free plots, based on measurements made at 11 experimental sites over a 2-year period. The mean reduction in yield was 49%. Two models were used to describe grain yield reduction in terms of C. arvense shoot density: (a) linear regression of percentage yield reduction on the square root of shoot density, and (b) non-linear regression, based on a rectangular hyperbola. Both models give similar yield loss estimates at commonly occurring shoot densities of C. arvense, but the non-linear model accounted for more of the observed variation in grain yield. The major yield component affected by C. arvense competition was spikes per unit area, with kernel weight affected to a lesser extent.     

A second survey of cereal weeds in central southern England

A survey of grass weeds of cereals in central southern England made in 1981 was repeated in 1982 between 28 June and 23 July. Dicotyledonous weeds were also assessed in 1982. A total of 1021 fields were surveyed, 702 in winter wheat. 198 in winter barley and 121 in spring barley. A total of twenty-four grass weeds were found and their levels of infestation were scored. The most frequently found grass weeds were the same as in 1981. In all cereals combined, these were Elymus (Agropyron) repens in 35% of fields, Avena fatua in 32%, Alopecurus myosuroides in 26% and Poa trivialis in 24%. Sixty-three species of dicotyledonous weeds were recorded and of these, eighteen species occurred in 2% or more of fields. The eight most frequent were Viola arvensis, Galium aparine, Stellaria media, Myosotis arvensis, Polygonum aviculare, Convolvulus arvensis, Bilderdykia (Polygonum) convolvulus and Lamium purpureum. Most species were fairly uniform in distribution, but Galium aparine, Convolvulus arvensis and Cirsium arvense were most frequent in the east while Viola arvensis was least frequent there. The cereals varied in weediness, 32% of winter barley, 23% of spring barley and only 7% of winter wheat fields had no weeds recorded.     

Seasonal dynamics of ground cover in Cirsium arvense – a basis for estimating grazing losses and economic impacts

Analysis of the economics of managing Cirsium arvense in grazed pastures worldwide has been hampered by a lack of data on the within‐year seasonal dynamics of the weed and its impact on the yield of palatable herbage. To redress this, the seasonal pattern in within‐patch percentage ground cover of the weed was determined from measurements on 39 dairy and 66 sheep and/or beef cattle farms in New Zealand during 2009–2010 and 2010–2011. This pattern was then scaled using farmer estimates of peak whole‐farm cover to derive mean monthly covers for dairy, beef, sheep/beef, sheep and deer farms. These monthly covers corresponded, respectively, to mean annual percentage covers of 2.7, 1.7, 3.0, 5.9 and 2.9% and to mean annual percentage losses in pasture growth (palatable herbage yield) of 3.6, 2.3, 4.0, 7.8 and 3.9%. The latter, in combination with 2011–2012 farm statistics, revealed that C. arvense caused a national loss in pastoral farm gross revenue in New Zealand in 2011–2012 of $685 million ($446 m dairy, $233 m sheep/beef, $6 m deer). Beyond the scope of this paper, the monthly covers and their corresponding monthly losses in pasture growth provide a basis for modelling the economic impacts of C. arvense and its management at a farm scale. More generally, the analytical method that we have developed is appropriate for evaluating the economic impact of any weed in a grazed pasture, particularly those exhibiting pronounced seasonal patterns in occupancy, such as annuals and deciduous perennials.     

Sprouting capacity from intact root systems of Cirsium arvense and Sonchus arvensis decrease in autumn

Perennial weeds are often controlled by mechanical means, which aim at stimulating axillary and adventitious buds to sprout. This happens when the apical dominance of the main shoot is removed by defoliation or when the underground system is fragmented. By repeating the measures, the result is a depletion of storage compounds, which weakens the plants and reduces their capacity to grow and reproduce. However, timing is critical. Earlier research has indicated that emergence from fragments of Sonchus arvensis cease during a period in autumn, while the seasonal pattern of sprouting in Cirsium arvense appears to be inconsistent. We studied the emergence pattern of defoliated plants with undisturbed root systems, from late summer to early spring. Potted plants grown outdoors were exhumed at regular intervals, put under forcing conditions for 4 weeks, after which shoots above and below soil level were counted and weighed together with the remaining root systems. In both species, the number and weight of emerged shoots decreased during a period in the autumn. In C. arvense, underground shoots were constantly produced during the same period, while fewer underground shoots were present in S. arvensis. For the latter species, apical dominance does not fully explain the effect; thus, endodormancy might be involved. Root weight increased until withering and did not explain the lack of emergence. Our results suggest an impaired sprouting capacity of undisturbed root systems of C. arvense and S. arvensis during September–October, which has implications for the timing and method of control of these species.     

Combining mechanical rhizome removal and cover crops for Elytrigia repens control in organic barley systems

Mechanical weed control of perennial weeds in organic crop production over long post‐harvest periods is incompatible with the establishment of cover crops for improving soil quality and preventing nutrient leaching. We suggest a new concept that comprises uprooting and immediate removal of vegetative propagules located within the plough layer to allow for quick re‐establishment of a plant cover. A field experiment comparing the effects of conventional practices (stubble cultivation) with different combinations of rotary cultivation (One, Two or four passes) and cover crops (none vs. rye‐vetch‐mustard mixture) on Elytrigia repens rhizome removal, shoot growth and suppression of a subsequent barley crop was examined in two growing seasons. Four passes with a modified rotary cultivator, where each pass was followed by rhizome removal, reduced E. repens shoot growth in barley by 84% and 97%. In general, the cover crop developed poorly and did not affect barley or E. repens. Barley yield was only affected by treatments in the first season, where yield was negatively correlated with E. repens shoot biomass. The concept has potential for the control of severe E. repens infestations, but future research aimed at identifying more effective smother crops and less intensive methods of rhizome removal is needed.     

水稻孕穗期稻茎毛眼水蝇经济阈值的研究

试验表明，水稻孕穗期每丛水稻茎毛眼水蝇卵数（Ｘ_１）、被害穗数（Ｘ_２）与产量损失（Ｙ）的关系符合下列方程：Ｙ＝－２．０１＋４．５２４Ｘ_１±２．２，ｒ＝０．９９１４；Ｙ＝－０．０７６＋４．９１２Ｘ_２±２．７８，ｒ＝０．９８６３。产量损失的主导因素是水稻受害后，早稻实粒数减少，晚稻总粒数和实粒数减少。根据防治费用，稻谷价格等，导出孕穗期稻茎毛眼水蝇的经济阈值为每丛禾１．９粒卵或１．３４株受害穗。经大田验证，与实际基本相符。     

小麦白粉病反应型和产孢量的关系

利用小麦的6个品种及小麦白粉菌的3个小种研究了小麦苗期白粉病反应型与产孢量之间的关系。分别用累积单斑产孢量(LBSY)、累积单位面积产孢量(LASY)与反应型组建了反应型-产孢量关系模型:Y_1=exp(1.7178×lnX 0.0256X-2.484)(LBSY法);Y_2=exp(1.5168×lnX 0.052X-2.309)(LASY法)(X为反应型,Y为产孢系数)。通过LBSY方法获得反应型0,1,2,3~-,3,3~ ,4~-,4所对应的产孢系数分别为0,0.09,0.29,0.49,0.60,0.71,0.96,1。     

Ray blight of pyrethrum in Australia: a review of the current status and future opportunities

Ray blight caused by Stagonosporopsis tanaceti is one of the most important diseases of pyrethrum (Tanacetum cinerariifolium), a perennial herbaceous plant cultivated for the extraction of insecticidal pyrethrins in Australia. The disease is responsible for complete yield loss in severe outbreaks. Infected seed is considered as the principal source of S. tanaceti. Infection hyphae remain only in the seed coat and not in the embryo, resulting in pre- and post-emergence death of seedlings and latent infection. Therefore, quantification of the level of infection by S. tanaceti within seed using a qPCR assay is important for efficient management of the disease. Stagonosporopsis tanaceti completes its life cycle within 12 days after leaf infection through production of pycnidia and can infect every tissue of the pyrethrum plant except the vascular and root tissues. Ray blight epidemics occur in pyrethrum fields through splash dispersal of pycnidiospores between adjacent plants. Besides steam sterilization, thiabendazole/thiram and fludioxonil are effective seed-treating chemicals in controlling S. tanaceti before planting begins. Ray blight is currently managed in the field through the foliar application of strobilurin fungicides in the first 1–2 years of crop establishment. Later on, difenoconazole and multisite specific fungicides in the next 2–3 years during early spring successfully reduce ray blight infestation. Avoiding development of resistance to fungicides will require more sustainable management of ray blight including the development and deployment of resistant cultivars.     

Tolerance of spring wheat (Triticum aestivum L.) to trifluralin deep-incorporated in the autumn or spring

Field experiments at Lacombe on a Ponoka loam soil (9·6% organic matter) during 1982 and 1983 investigated the tolerance of spring wheat (Triticum aestivum L.) cv. Neepawa in a weed free situation to trifluralin applied at 0·0–3·0 kg ai ha^?1 in the autumn or spring and incorporated to a depth of 10 cm. Rates of trifluralin above 1·0 kg ai ha^?1 applied in the autumn or spring reduced the percent stand of wheat compared to an untreated control. Two weeks after emergence the crop showed 37 or 47% injury indicated by delayed growth, following application at 1·0 kg ai ha^?1 in the autumn or spring, respectively. The wheat recovered throughout the course of the growing season. At harvest, trifluralin applied in the autumn or spring at rates below 1·0 kg ai ha^?1 caused a yield increase while higher rates caused a yield decrease compared to the untreated control. Spring application caused a greater yield loss than autumn application. The tolerance of spring wheat to trifluralin at rates required for weed control (1·1 kg ai ha^?1 or higher) on this soil type is marginal.     

Evaluation of three empirical models depicting Ambrosia artemisiifolia competition in white bean

The performance of three empirical models describing white bean yield loss (Y_L) 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=10^oC) 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.     

北京地区春玉米螟害产量损失估计方法及防治指标的商榷

根据1962—1964年北京地区12块春播玉米地心叶期卵和卵虫(第一代)成活率資料,并参考国内对螟害与玉米产量損失关系的研究成果,提出了春玉米上因玉米螟为害而造成的产量損夫估計方法和药剂防治的参考指标。心叶期卵的平均成活率及其标准誤为57.4±2.9％,卵块的脫落是死亡的主要原因。幼虫期的平均成活率及其标准誤为5.64±0.89％。这两个平均成活率的变異系数都比较小,相关分析表明,百株着卵量与成长幼虫数是相关的。故可职利用卵和幼虫的平均成活率由着卵密度来估計成长幼虫密度。心叶期卵和幼虫的合計平均成活率及其标准誤为3.4±0.51％。在95％可靠性时的置信区間为3.4±1.173％,卵块的平均粒数为31.7粒。若职单株平均一虫所造成的产量損失率为5％計,可用丁式来估計产量損失: 产量損失％=[(心叶期百株累計卵块数×31.7)×(0.034±0.012)]×0.05 在經济核算士,作者初步認为职損失率1.5％作为防治标准比較合适。以此推算,欲达到这一損失率,心叶期百株累計卵块应为28块(用平均成活率計算)至21块(用成活率上界計算)。一般可定为24块。根据心叶期百株累計卵块数与累計着卵株百分率或百株高峯卵块数之間存在的相关,百株累計24块卵,相当于累計着卵株率28％,或百株高峯卵块6块。在实践上就可以用它們作为心叶期的防治指标。     

Control of Achillea millefolium L. (yarrow) by rotary cultivation and glyphosate

Various control strategies for Achillea millefolium L. (yarrow) were investigated in a dense stand of the weed at Lincoln College in 1977–1978. In early spring plots were either rotary cultivated or left undisturbed. In late spring, plots of both previous treatments were either left undisturbed, rotary cultivated or sprayed with glyphosate at 1·5 kg ha^?1. The whole experiment was rotary cultivated twice 1 week later and sown with Hordeum vulgure L. cv. Zephyr (barley) at 144 kg seed ha^?1. MCPA + dicamba at 0·9+0·15 kg ha^?1 was applied to half of each plot when the second node was detectable (Zadok 32). Rotary cultivation and glyphosate both substantially reduced the regrowth of A. millefolium but glyphosate reduced regrowth by a greater proportion when applied to undisturbed plants than when applied to plants regenerating after cultivation. Both gave a more than 95% reduction compared to the control (rotary cultivation only at sowing time) in the amount of A. millefolium present in the barley stubble in the autumn. MCPA + dicamba caused seedling mortality but did not affect the numbers of primary shoots from rhizome fragments. The grain yield of the barley increased from 2·91 t ha^?1 when A. millefolium was not controlled to 4·23 t ha^?1 with good control. The barley yield appeared to be restricted by competition from regenerating A. millefolium and by a nitrogen deficiency induced in some regimes by nitrogen immobilization in decaying rhizomes.     

小麦禾谷缢管蚜的危害损失和防治指标研究

禾谷缢管蚜种群数量和危害历期是造成小麦产量损失的主要因素。采用累积虫日作为危害量指标 ,建立了蚜虫危害量与小麦产量损失的回归模型 ,即Y₁=1.4250+5.3529×10^-4X₁,Y₂=1.1780+0.0106X₂ ,确定了禾谷缢管蚜的动态防治指标     

Impacts of applied Sclerotinia sclerotiorum on the dynamics of a Cirsium arvense population

A field experiment was conducted from October 1992 to March 1997 in a sheep‐grazed pasture in Canterbury, New Zealand, to determine the effects of the fungus Sclerotinia sclerotiorum on the long‐term dynamics of a population of Cirsium arvense. The pathogen was applied in mid‐spring either once or in three consecutive years when the C. arvense shoots were vegetative rosettes, using a granular, mycelium‐on‐wheat preparation that lodged on the C. arvense leaves, stems and in the leaf axils. The single application caused disease in the C. arvense that was confined to the application year. The disease resulted in a temporary (17 months) reduction in population size through initial mortalities among treated shoots and resultant reductions in root growth, adventitious root bud, subterranean shoot and, subsequently, aerial shoot population sizes. The soil seedbank was 80% lower in the treated plots than in the control plots in the first year. Seedlings were never found. The annually repeated application of S. sclerotiorum did not result in the expected continuing decline in the C. arvense population relative to the control population.     

烟草赤星病危害烤烟产量产值损失测定

在烤烟生长中后期 ,应用40%菌核净500倍液人为控制烟草赤星病发生程度 ,形成不同危害梯度 ,以研究烟草赤星病对产量产值的影响。经试验分析 ,建立数学模型。中上等烟产量损失率(Y₁)与病情指数(X)的关系式:Y₁=0.1516+1.2824X;产值损失率(Y₂)与病情指数(X)的关系式:Y₂=0.3239+0.9831X。     

Some studies of competition between Avena fatua L. and spring barley I. The influence of A. fatua on yield of barley

A. fauta reduced yields of spring barley in the majority of 51 experiments carried out during 1971 and 1972. Infestations ranging from 8 to 662 seedlings/m² in the spring resulted in yield reductions varying from nothing to 72%; in 11 experiments these exceeded 1–2 t/ha. Reductions in yield were poorly correlated with numbers of seedlings, panicles or wild oat seeds produced. However, there was a good correlation between yield loss and the dry weight of wild oats at harvest. Growth and competitive effects of wild oats differed between the two years. Grain losses were due mainly to reductions in the numbers of ear bearing barley tillers. The influence and significance of the effect of competition on the size of barley grains is discussed.