油菜田间杂草防控策略研究进展

为了研究油菜全程机械化栽培技术，筛选出适宜西安地区种植的丰产性好、适应性广、抗逆性强的优质油菜机械化种植新品种及配套栽培技术，为大面积推广提供依据，推动油菜全程机械化栽培技术的发展步伐，西安市农技中心技术人员连续三年在临潼万邦农业示范园开展油菜新品种全程机械化栽培技术试验示范，总结出适宜西安市油菜栽培的全程机械化轻简栽培技术，以期对油菜种植户提供技术指导。

使用除草剂是根除作物田里杂草的有效方法，其中以乙酰乳酸合成酶(acetolactate synthetase, ALS)为靶标的除草剂在杂草防治方面有很好的应用价值。本文对乙酰乳酸合成酶的结构、ALS抑制剂类除草剂种类、抗除草剂植物抗性机理、抗ALS抑制剂类除草剂作物的研究进展进行了综合概括。

乙酰辅酶A羧化酶(ACCase)是脂肪酸合成途径中的关键酶之一，在植物体内，ACCase是多种除草剂的作用靶标。本论文针对ACCase抑制剂类除草剂的种类和使用情况，以及ACCase靶标抗性及水稻非靶标抗性机制的相关研究进行简单概述。

川渝山地区域典型的山地特征和农耕传承承载了山区人们的生产生活，近60年的农化种植，给土地、环境、粮食安全及人们健康造成了严重的影响。去除农化、修复改良土壤、保护环境、保障农产品安全、保护健康、保护优良传承已经刻不容缓。采用酵素进行改良土壤、代替农药化肥除草剂进行生态种植，对于川山地区生态农业研究与实践应用方面取得了一定的成效。将川山农耕现状和生态种植进行深刻剖析，以及酵素将应用于生态种植的技术方法进行推广，有利于更多的川山人们特别是农人农户们的生产生活保障和身体健康，也是助农生态增收、实现绿色经济发展、助力生态乡村振兴的有效举措。

目的：为了研究直播油菜密度及其与产量、植株性状、品质性状的相关关系。方法：通过考查648个甘蓝型杂交油菜新组合的密度、单株产量、株高、千粒重、角粒数、主花序角果长度、单株角果数、有效分枝位、一次分枝数、主序长度，并分析各组合的硫苷、含油率、种子蛋白质、油酸、亚油酸、亚麻酸、棕榈酸、硬脂酸、二十碳烯酸9个性状。结果：直播油菜获得最高产量的密度为46.0833万株/hm2。主花序角果数占单株角果数的3/5以上。直播油菜的有效分枝部位(0.1800**)与密度间呈极显著正相关，株高(−0.2830**)、主序长(−0.4401**)、一次分枝数(−0.3731**)、单株角果数(−0.4312**)、单株产量(−0.4526**)、角粒数(−0.1269**)、主花序角果长度(−0.1204**)与密度间均呈极显著负相关，千粒重(−0.0554)与密度间的相关未达到显著水平，收获指数(−0.20298)与密度间呈极显著负相关。含油率(−0.3719**)、油酸(−0.2371**)与产量呈极显著负相关，蛋白质(0.5657)、亚油酸(0.2168**)、亚麻酸(0.2414**)、二十碳烯酸(0.2135**)与产量呈极显著正相关，硫苷(−0.0462)、硬脂酸(0.0247)、棕榈酸(−0.0253)与产量间的相关均未达到显著水平。结论：提高甘蓝型杂交油菜的产量，油菜籽的含油率、油酸含量降低，种子蛋白质、亚油酸、亚麻酸、二十碳烯酸含量增加。增加密度，有效分枝部位增高，株高和单株产量降低、主花序和主花序角果长度变短、一次分枝数、单株角果数、角粒数减少。

喜旱莲子草是一种入侵我国的恶性杂草，自入侵以来快速传播和蔓延，造成了巨大的生态环境危害和经济损失。目前，对于该草的防控研究已取得了较大进展，但有些地区的防控问题仍未解决，全球气候变化和氮沉降又给防控形势带来了新的考验。本文概述了喜旱莲子草在我国的潜在空间分布及主要防控手段，提出了一些目前存在的问题及建议，以期为今后有效防控该杂草提供指导。

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Summary Two winter oilseed rape ( Brassica napus ) cultivars, tolerant to glyphosate and glufosinate, were compared with a conventional cultivar at three sites over 4 years, in 3‐year crop rotations in the UK. The winter oilseed rape was grown in Years 1 and 4, with winter cereals, which received uniform herbicide treatments, in the intervening years. The second winter oilseed rape treatments were applied to randomised sub‐plots of the original plots. Weed densities were recorded in autumn and spring and weed biomass was measured in summer. At most sites, there was only one application of glufosinate or glyphosate, whereas two products were often used on the conventional variety. The timing of glyphosate and glufosinate application was, on average, 34 days later than that of the conventional broad‐leaved weed control treatments. Overall weed control, across all sites and years, was not statistically different between the conventional, glyphosate and glufosinate treatments. However, glyphosate achieved higher control of individual weed species more frequently than the other treatments. Glufosinate and the conventional treatments were similar in performance. The treatments in Year 1 sometimes affected weed populations in the subsequent cereal crops and, in rare instances, those in the rape in Year 4. Carry‐over effects were small after most treatments. In general, weed survival was greater in the oilseed rape crops, irrespective of the treatment, than it was in the intervening cereal crops.

Field experiments were carried out at the Agricultural Research Station, Faculty of Agriculture, University of Tabriz, in 2004-2005 and 2005-2006. Three winter oilseed rape cultivars (Okapi, Licord, and SLM046) with 12 weed interference durations were evaluated in a factorial experiment based on a randomized complete block design with 3 replications. The experiments consisted of 2 sets of treatments. In the first set, the crop was kept weed-free until the growth stages of 4-leaf, 8-leaf, stem elongation, flowering, and podding. In the second set, weeds were permitted to grow within the crop until the above-mentioned growth stages. Weedy and weed-free checks were also included in the study. Different weed interference durations and interaction of cultivar * year affected significantly the grain, oil, and biological yield, but not the percentage of oil. Minimum values of these traits were observed under the full weed-infestation condition. Maximum values for grain yield, oil and biological yield belonged to the weed free control and SLM046 cultivar in both years. Regression models showed that in order to prevent >10% grain and oil yield loss, canola must be kept weed free between the 6-leaf stage and initial flowering (47-110 DAE) and for biological yield between the 7-leaf stage and stem elongation (52-94 DAE).

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N-(2-Bromophenyl)-2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamine is a highly active herbicide, which belongs to a novel class of chemistry. The compound is de novo synthesized in good yield, and the structure is confirmed by (1)H NMR, IR, MS, microanalysis, and X-ray. Its herbicidal activity is assessed under greenhouse conditions. It is effective against many grass weed species, as well as broadleaf weeds, under greenhouse conditions. Field trials indicate that it controls major weeds with a good tolerance on oilseed rape by postemergence application at rates of 15-90 g of active ingredient/ha. This compound possesses low mammalian toxicity and favorable environmental profile. These results suggest that the compound has potential as a new selective postemergent herbicide in winter oilseed rape.

Weed control was more efficient than thermal. Application of plant bio-activators increased the efficiency of the thermal weed control.

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A field experiment was conducted during the 2014–2017 period at Aleksandras Stulginskis University (now—Vytautas Magnus University Agriculture Academy) on a Endocalcaric Endogleyic Luvisol (LV-can.gln) according to the WRB 2014. The three nonchemical weed control methods were explored: (1) thermal (using wet water steam), (2) mechanical (interrow loosening), and (3) self-regulation (smothering). In the thermal and mechanical weed control treatments, winter oilseed rape was grown with an interrow spacing of 48.0 cm and in weed smothering (self-regulation) treatment with an interrow spacing of 12.0 cm. Winter oilseed rape was grown in the soil with a regular humus layer (23–25 cm) and with a thickened humus layer (45–50 cm). Annual weeds predominated in the winter oilseed rape crop. In the soil with both humus layers, regular and thickened, the most efficient weed control method was mechanical weed management both during the autumn (efficacy 26.7–75.1%) and spring (efficacy 37.1–76.7%) growing seasons. Thermal and mechanical weed control in combination with the bio-preparations in droughty years significantly reduced the number of weed seedlings. Dry matter mass of weeds most markedly decreased through the application of the mechanical weed management method.

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This study aims to determine the impact of different non-chemical weed control systems on organically grown spring oilseed rape ( Brassica napus L.) crop weediness and yield of seeds. Non-chemical weed control systems: 1) thermal (water steam), 2) mechanical (inter-row loosening), and 3) smothering (self-regulation). Thermal (1.5–1.8 times) and mechanical (2.5–6.8 times) weed control systems significantly reduced the number of weed seedlings in spring oilseed rape crop, compared with the weed smothering system. The most effective system of weed control in rape crop was mechanical (efficiency 30.9–75.5 %). Efficiency of thermal weed control system, compared with mechanical, was lower, 28.4–40.0 %. Before rape harvesting in plots where mechanical weed control was applied, compared with plots where weed smothering was used, the number of weeds was significantly 3.2–4.4 times lower, and dry matter mass of weeds was 2.2–3.1 times lower. The yield of rape seeds increased with increasing efficiency of thermal and mechanical weed control. In 2014, the yield of rape seeds depended on number of weed seedlings and dry matter mass of weeds before rape harvesting. Keywords: spring oilseed rape, weed control systems, weed, yield, organic farming

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Oilseed rape (Brassica napus L.) is grown widely across the world as a constituent of arable crop rotations. Many of the weeds to occur in oilseed rape are common to those of cereal crops that tend to dominate rotations, but their relative importance does differ. For example, annual grass weeds are a major problem, as they are in cereals, but weeds of the Brassicaceae (eg Sinapis arvensis L., Raphanus raphanistrum L.) tend to be of greater significance in rape, as herbicide selectivity is more of a challenge. Spring-sown oilseed rape tends to have a different flora to autumn-sown rape, due to the differences in weed emergence periodicity. For example, Chenopodium album L. and Fallopia convolvulus (L.) A. Love are more significant in spring rape, whilst Papaver rhoeas L. and Galium spp. ¬are more important in winter rape. The major impact of weeds is on crop growth and yields, though they can also adversely affect harvesting and contaminate the harvested rape seeds. Cultural control of weeds in oilseed rape can be achieved with varying degrees of effectiveness by adjusting cultivation practices and crop agronomy. Shallow non-inversion tillage and direct drilling have become increasingly prevalent in recent years, for environmental and economic reasons, and potentially can reduce weed emergence in rape, though this is very dependent on minimising weed seed return in the previous crop. Sowing the crop in optimum conditions is critical to ensuring the best competitive effect from the crop, as a vigorous stand will suppress many weeds. In contrast, a poor crop will be much more vulnerable to weeds. Adjusting the agronomy of the crop to achieve good weed suppression is encouraged worldwide, for example: sowing early in the autumn when higher temperatures favour the crop, increasing seed rates (despite the added cost), using more competitive cultivars. Most weed control in the developed world is based on herbicides which in the past have delivered good weed suppression but in recent years the rise of herbicide resistance, especially in grass weeds, has made weed control more difficult. Mechanical weed control has not been widely practiced in intensive production systems. Herbicide tolerant cultivars have been developed both by conventional breeding (triazine, imidazolinone resistance) and by genetic modification (glyphosate and glufosinate resistance). The former has been adopted on a limited area in many countries but the latter (GMHT) cultivars dominate production in N. America whilst not being approved in Europe. Resistance to glyphosate is not yet common in Canadian rape crops though is commoner in the USA, where GMHT crops have been grown more intensively. Herbicide resistant cultivars have provided tools for farmers to overcome other forms of resistance, however, their longer-term success in the future is questionable. In Europe where GMHT crops are not approved, herbicide resistance in grass weeds remains a serious problem. This is compounded by the presence of alternative products used to overcome resistance, such as propyzamide, appearing in ground and surface waters, breaching EU standards for pesticides in water. Thus, weed control in oilseed rape across the world is not easy and the traditional herbicide based model is failing for a variety of reasons. There are no alternative herbicide tools for the immediate future and thus farmers need to take a more integrated approach to their weed management, combining optimum agronomic practices with reduced use of herbicides to manage their weeds. Attention to detail in management practices to minimise weed presence at drilling is, and will be, of increasing importance. Modern 21st Century practices such as GPS navigation and computer-based engineering technologies are beginning to support more integrated management practices.

We compared the seedbanks, seed rains, plant densities and biomasses of weeds under two contrasting systems of management in beet, maize and spring oilseed rape. Weed seedbank and plant density were measured at the same locations in two subsequent seasons. About 60 fields were sown with each crop. Each field was split, one half being sown with a conventional variety managed according to the farmer's normal practice, the other half being sown with a genetically modified herbicide-tolerant (GMHT) variety, with weeds controlled by a broad-spectrum herbicide. In beet and rape, plant densities shortly after sowing were higher in the GMHT treatment. Following weed control in conventional beet, plant densities were approximately one-fifth of those in GMHT beet. In both beet and rape, this effect was reversed after the first application of broad-spectrum herbicide, so that late-season plant densities were lower in the GMHT treatments. Biomass and seed rain in GMHT crops were between one-third and one-sixth of those in conventional treatments. The effects of differing weed-seed returns in these two crops persisted in the seedbank: densities following the GMHT treatment were about 20% lower than those following the conventional treatment. The effect of growing maize was quite different. Weed density was higher throughout the season in the GMHT treatment. Late-season biomass was 82% higher and seed rain was 87% higher than in the conventional treatment. The difference was not subsequently detectable in the seedbank because the total seed return was low after both treatments. In all three crops, weed diversity was little affected by the treatment, except for transient effects immediately following herbicide application.

Abstract The sulfonylurea herbicides are characterized by broad‐spectrum weed control at very low use rates (c. 2–75 g ha −1 ), good crop selectivity, and very low acute and chronic animal toxicity. This class of herbicides acts through inhibition of acetolactate synthase (EC 4.1.3.18; also known as acetohydroxyacid synthase), thereby blocking the biosynthesis of the branched‐chain amino acids valine, leucine and isoleucine. This inhibition leads to the rapid cessation of plant cell division and growth. Crop‐selective sulfonylurea herbicides have been commercialized for use in wheat, barley, rice, corn, soybeans and oilseed rape, with additional crop‐selective compounds in cotton, potatoes, and sugarbeet having been noted. Crop selectivity results from rapid metabolic inactivation of the herbicide in the tolerant crop. Under growth‐room conditions, metabolic half‐lives in tolerant crop plants range from 1–5 h, while sensitive plant species metabolize these herbicides much more slowly, with half‐lives > 20 h. Pathways by which sulfonylurea herbicides are inactivated among these plants include aryl and aliphatic hydroxylation followed by glucose conjugation, sulfonylurea bridge hydrolysis and sulfonamide bond cleavage, oxidative O‐demethylation and direct conjugation with (homo)glutathione. Sulfonylurea herbicides degrade in soil through a combination of bridge hydrolysis and microbial degradation. Hydrolysis is significantly faster under acidic (pH 5) than alkaline (pH 8) conditions, allowing the use of soil pH as a predictor of soil residual activity. Chemical and microbial processes combine to give typical field dissipation half‐lives of 1–6 weeks, depending on the soil type, location and compound. Very short residual sulfonylurea herbicides with enhanced susceptibility to hydrolysis (DPX‐L5300) and microbial degradation (thifensulfuron‐methyl) have been developed.

The framework conditions for chemical weed control in oilseed rape (OSR) are becoming increasingly unfavorable in Central Europe. On the one hand, weed resistance is spreading and, on the other, there is a growing social desire to reduce or eliminate the use of chemical crop protection products. In a field experiment, hoeing, as a weed control measure performed two times per growing season (one time in autumn and one time in spring) in oilseed rape (Brassica napus; two varieties), was compared to chemical control by herbicides and a combination of hoeing and herbicide application (five treatments altogether). The chemical control by herbicides consisted of a broad-spectrum pre-emergence treatment and a post-emergence graminicide application. The trial was set up in each of three periods (years 2014/2015, 2015/2016, and 2016/2017) at the experimental station Ihinger Hof, University of Hohenheim, Stuttgart, Germany. The effect of the treatments on weed plant density, weed biomass at the time of harvesting, and on OSR grain yield was investigated. Weed plant density was measured four times per trial year, each time before and after hoeing. In 2015/2016 after spring hoeing, and in 2016/2017 at all data collection times, weed plant density was significantly higher in hoeing without herbicide application than in the other variants. No significant differences occurred at the other data collection times. The weed plant density ranged from 0.5 to 57.8 plants m−2. Regardless of the trial year, pure hoeing always resulted in a significantly higher weed biomass at the time of harvesting than the herbicide applications or the combinations. The weed biomass at the time of harvesting ranged between 0.1 and 54.7 g m−2. No significant differences in grain yield between hoeing and herbicide application occurred in all three trial years. According to the results, hoeing is a suitable extension of existing integrated weed control strategies in OSR.

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Summary Glyphosate is a key component of weed control strategies in Australia and worldwide. Despite widespread and frequent use, evolved resistance to glyphosate is rare. A herbicide resistance model, parameterized for Lolium rigidum has been used to perform a number of simulations to compare predicted rates of evolution of glyphosate resistance under past, present and projected future use strategies. In a 30‐year wheat, lupin, wheat, oilseed rape crop rotation with minimum tillage (100% shallow depth soil disturbance at sowing) and annual use of glyphosate pre‐sowing, L. rigidum control was sustainable with no predicted glyphosate resistance. When the crop establishment system was changed to annual no‐tillage (15% soil disturbance at sowing), glyphosate resistance was predicted in 90% of populations, with resistance becoming apparent after between 10 and 18 years when sowing was delayed. Resistance was predicted in 20% of populations after 25–30 years with early sowing. Risks of glyphosate resistance could be reduced by rotating between no‐tillage and minimum‐tillage establishment systems, or by rotating between glyphosate and paraquat for pre‐sowing weed control. The double knockdown strategy (sequential full rate applications of glyphosate and paraquat) reduced risks of glyphosate and paraquat resistance to <2%. Introduction of glyphosate‐resistant oilseed rape significantly increased predicted risks of glyphosate resistance in no‐tillage systems even when the double knockdown was practised. These increased risks could be offset by high crop sowing rates and weed seed collection at harvest. When no selective herbicides were available in wheat crops, the introduction of glyphosate‐resistant oilseed rape necessitated a return to a minimum‐tillage crop establishment system.

Noninversion tillage with tine- or disc-based cultivations prior to crop establishment is the most common way of reducing tillage for arable cropping systems with small grain cereals, oilseed rape, and maize in Europe. However, new regulations on pesticide use might hinder further expansion of reduced-tillage systems. European agriculture is asked to become less dependent on pesticides and promote crop protection programs based on integrated pest management (IPM) principles. Conventional noninversion tillage systems rely entirely on the availability of glyphosate products, and herbicide consumption is mostly higher compared to plow-based cropping systems. Annual grass weeds and catchweed bedstraw often constitute the principal weed problems in noninversion tillage systems, and crop rotations concurrently have very high proportions of winter cereals. There is a need to redesign cropping systems to allow for more diversification of the crop rotations to combat these weed problems with less herbicide input. Cover crops, stubble management strategies, and tactics that strengthen crop growth relative to weed growth are also seen as important components in future IPM systems, but their impact in noninversion tillage systems needs validation. Direct mechanical weed control methods based on rotating weeding devices such as rotary hoes could become useful in reduced-tillage systems where more crop residues and less workable soils are more prevalent, but further development is needed for effective application. Owing to the frequent use of glyphosate in reduced-tillage systems, perennial weeds are not particularly problematic. However, results from organic cropping systems clearly reveal that desisting from glyphosate use inevitably leads to more problems with perennials, which need to be addressed in future research.

The determination of critical period of weed control in oilseed rape is necessary to know the weed control period. To determine the critical period, two fields experiments were carried out during 1995-96 growth season in Loukkos and Saïs regions at two oilseed densities (D1 = 24 and D2 = 36 plants m(-2)). Ten treatments corresponding to plots left weed free or weeded plots until four leaves, flowers bud, flowering, puds formation, and maturity stages of oilseed rape were tested. Density and biomass of weeds were determined at each oilseed stages. Results showed that weed density and biomass were higher in Saïs than in Loukkos sites. For a 10% yield loss, critical period of weed control in Loukkos was from 458 to 720 degree days after emergence (D degrees AE) and from 480 to 720 D degrees AE in oilseed conducted at densities D1 and D2, respectively. In Saïs, critical period of weed control was from 474 to 738 D degrees AE and from 468 to 675 D degrees AE in oilseed conducted at D1 and D2, respectively. It was concluded that the length of the critical period of weed control in oilseed rape grain yield seems to be dependant of the level of the infestation.

e-ISSN 2335-8947

The competitive ability of weeds against crop plants is determined by the amount of macronutrients taken up from the soil. Macronutrient uptake is influenced by nutrient concentrations in plants and, above all, the amount of weed biomass produced per unit area. The present study was conducted as a part of a field experiment with winter oilseed rape, which has been carried out since 1967. Winter oilseed rape has been grown continuously since 1967 in the same field and in a six-field crop rotation. In winter oilseed rape monoculture, weed management was implemented to mitigate soil fatigue. Winter oilseed rape yields were twice as high in crop rotation than in monoculture, and weed biomass was more than three times higher in the continuous cropping system than in crop rotation. Winter oilseed rape yields were higher in crop rotation without a weed control than in monoculture, including monoculture with a weed control. Nitrogen (N) uptake by rape seeds and straw was significantly higher, whereas N uptake by weeds was lower in crop rotation than in monoculture. In all years of this study, N uptake by weed biomass was higher in monoculture than in crop rotation due to higher weed infestation levels in the continuous cropping system, and N uptake was not significantly affected by N content. The weed control induced a greater increase in N uptake by rape seeds and straw in monoculture than in crop rotation. The results indicate that integrating crop rotation with herbicide protection can help increase yields while reducing weeds, which promotes a more sustainable crop production system. The use of crop rotation contributes to a more efficient use of nitrogen by crops, while reducing its uptake by weeds.

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The current study was aimed to establish the impact of non-chemical weed control methods (thermal, mechanical andsmothering) and biopreparations on winter oilseed rape (Brassica napus L.) preparation for over-wintering and productivity under the conditions of the organic farming system. During the 2014–2016 period, a field experiment was conducted at the Experimental Station of Aleksandras Stulginskis University on Calc(ar)i-Endohypogleyic Luvisol (LVg-n-w-cc). The field experiment treatments were the following: Factor A – non-chemical weed control methods: 1) thermal (water steam), 2) mechanical (inter-row loosening), 3) smothering (self-regulation, sowing with narrow inter-rows); Factor B – application of biopreparations: 1) without application, 2) with application. During the period of autumn vegetation, in the smothering method plots, where the winter oilseed rape crop density was 1.5–2.4 times lower than that in the plots of thermal and mechanical weed control methods, the significantly highest aboveground mass of plant, number of leaves per plant, diameter of root collar, root area, total root length, root biomass of plant and leaf area of plant were determined, and in 2015 the highest chlorophyll index was measured in the leaves. In 2014 the application of biopreprations in the smothering method plots significantly increased the aboveground mass of plant (41.3%), the total root length (33.2%) and the root biomass of plant (28.0%). In 2004 the diameter of winter oilseed rape root collar depended on the leaf area of plant (r = 0.83, P < 0.05) and the root area of plant (r = 0.86, P < 0.05), and in 2015 it depended on the leaf area of plant (r = 0.89, P < 0.05), the root area (r = 0.99, P < 0.01), the total root length (r = 0.98, P < 0.01) and the root biomass of plant (r = 0.99, P < 0.01). Positive, strong and very strong, and statistically significant relationships were established between the leaf area of oilseed rape and the root area, the total root length and the root biomass of plant. In the spring of 2015, during the renewed oilseed rape vegetation stage, the highest crop density (98.0 units m–2) and over-wintering (96.0%) were obtained in the plots of the mechanical weed control method in combination with biopreparations. In the spring of 2016, different nonchemical weed control methods and biopreparations did not have any significant effect on the oilseed rape over-wintering and the crop density. In 2015, different non-chemical weed control methods did not have any significant influence on oilseed rape biometric parameters before harvesting. In 2016, in the smothering method plots a significantly lower mass of oilseed rape and the number of branches per plant were formed compared to those of other used treatments. The highest number of pods per plant was determined in the smothering method plots in combination with biopreparations. In 2015 biopreprations in the smothering method plots significantly increased the 1 000 seed mass, and in 2016 they increased the number of pods per plant, respectively 7.2 and 35.6%. In the droughty year of 2015, the significantly highest winter oilseed rape seed yield was recorded in the plots of the mechanical weed control method, and in the moist year of 2016, the highest yield was in the smothering method plots with biopreparations. In 2015 biopreprations significantly increased the oilseed rape seed yield in the plots of thermal and mechanical weed control methods, and in 2016 they increased the yield in the smothering method plots, respectively 43.4, 25.1 and 51.5%. In 2015 the winter oilseed rape seed yield depended on the crop density (r = 0.86, P < 0.05) and the plant height (r = 0.94, P < 0.01), and in 2016 it depended on the number of pods per plant (r = 0.98, P < 0.01) and the plant height (r = 0.85, P < 0.05).

Summary There is a lack of information on the combined effects of preceding crop, reduced tillage (especially no‐tillage) and the time of herbicide application on the development of weed populations and the efficiency of weed control in winter wheat in humid temperate climates. An experiment was conducted with a crop rotation (winter wheat – oilseed rape – winter wheat – maize) on a sandy loam and a loamy silt soil in the Swiss midlands to investigate the impact of different preceding crops and pre‐ and post‐emergence control of weeds in conventional tillage (CT; mouldboard plough), minimum tillage (MT; chisel plough) and no‐tillage (NT; no soil disturbance systems). When winter wheat was grown after maize and winter wheat was grown after oilseed rape, the ranking order of weed density in treatments without herbicide application was NT < MT < CT and CT < MT < NT respectively. Analysis of variance and canonical discriminant analysis showed that Epilobium spp., Sonchus arvensis , Myosotis arvensis and volunteer crops were more abundant in NT than in MT and CT. The efficiency of post‐emergence weed control was generally better than that of pre‐emergence weed control, regardless of tillage intensity.

e-ISSN 2335-8947

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Summary Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post‐emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers’ practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.

1. Assuring future food productivity and security will require that better use is made of pest regulation provided by naturally occurring ecological services. However, empirical evidence of large-scale regulatory effects that might be employed in agriculture is still relatively scarce. 2. Using data from 257 conventionally managed arable fields at the UK national scale, we examine whether changes in the long-term store of weed seed in the seedbank are consistent with regulation by seed predatory carabid beetles. 3. We test three expectations of a simple conceptual model for carabid seed predation. The relationships we estimate are consistent with the model and suggest that carabid predation of weed seeds shed onto the soil surface changes the amount of seed returned to the seedbank bringing about seedbank change and regulation. 4. Granivorous and omnivorous carabids regulated seedbank abundance, with effects being observed on monocotyledon seedbank abundance, in all crops, and on total seedbank abundance, in spring maize and winter oilseed rape; effects that were robust across fields with differing pesticide management and between regions of the UK. 5. We found evidence of density dependence, with increasing amounts of seed rain leading to stronger regulation of the seedbank. 6. Our results also suggest that correlations between seed predators and seed rain abundance, which might be used to infer important effects of seed predators, do not provide sufficient evidence to indicate regulation of the weed seedbank. 7. Synthesis and applications. A major challenge for the future is to manage ecological, pest control services in place of current pesticides with little or no additional risk to productivity and food security. Our work shows that carabid seed predators have regulatory effects on the seedbank that appear general and robust across a range of current cropping and farm management situations at the national scale. Environmental Stewardship methods already exist across Europe to enhance carabid numbers in farmland. This means that carabid seed predators fit within a working framework that could be used to promote integrated pest management alongside or even in place of herbicides.

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Mixing plant species in agroecosystems is highlighted as an agroecological solution to reduce pesticides and fertilizers while maintaining profitability. In the French context, intercropping frost-sensitive legume crops with winter oilseed rape is potentially interesting and began to be implemented by farmers. In this study we aimed at measuring the services and disservices of this intercrop with three different legume mixtures, in terms of growth and yield for rapeseed, ground cover of weeds in autumn and damage caused by rape winter stem weevil. The experiment was carried out at four sites from 2011 to 2014. We showed higher total aerial dry weights and total aerial nitrogen contents in the intercrops compared to sole winter oilseed rape in November. The companion plants contributed to the control of weeds and the mitigation of rape winter stem weevil damage, notably through the increase in the total aerial weight. In spring, after destruction of the companion plants, the intercrops had partially compensated a reduction in the N fertilization rate (–30 kg per hectare) in terms of aerial nitrogen content in rapeseed, with no consequences on the yield which was maintained or even increased. There were probably other interactions such as an improvement in rapeseed root exploration. The consequences were an increase in the nitrogen use efficiency in intercrops. The intercrop with faba bean and lentil showed the best results in terms of autumn growth, weed control, reduction in rape winter stem weevil damage, and rapeseed N content in spring and yield. Intercropping frost-sensitive legume crops with winter oilseed rape is thus a promising way to reconcile yield and reduction in pesticides and fertilizer use and perhaps to benefit more widely to the cropping system.

Winter oilseed cash cover crops are gaining popularity in integrated weed management programs for suppressing weeds. A study was conducted at two field sites (Fargo, North Dakota, and Morris, Minnesota) to determine the freezing tolerance and weed-suppressing traits of winter canola/rapeseed (<i>Brassica napus</i> L.) and winter camelina [<i>Camelina sativa</i> (L.) Crantz] in the Upper Midwestern USA. The top 10 freezing tolerant accessions from a phenotyped population of winter canola/rapeseed were bulked and planted at both locations along with winter camelina (cv. Joelle) as a check. To phenotype our entire winter <i>B. napus</i> population (621 accessions) for freezing tolerance, seeds were also bulked and planted at both locations. All <i>B. napus</i> and camelina were no-till seeded at Fargo and Morris at two planting dates, late August (PD1) and mid-September (PD2) 2019. Data for winter survival of oilseed crops (plants m^-2) and their corresponding weed suppression (plants m^-2 and dry matter m^-2) were collected on two sampling dates (SD) in May and June 2020. Crop and SD were significant (<i>p</i> < 0.05) for crop plant density at both locations, and PD in Fargo and crop x PD interaction in Morris were significant for weed dry matter. At Morris and Fargo, PD1 produced greater winter <i>B. napus</i> survival (28% and 5%, respectively) and PD2 produced higher camelina survival (79% and 72%, respectively). Based on coefficient of determination (<i>r</i>²), ~50% of weed density was explained by camelina density, whereas ≤20% was explained by <i>B. napus</i> density at both locations. Camelina from PD2 suppressed weed dry matter by >90% of fallow at both locations, whereas weed dry matter in <i>B. napus</i> was not significantly different from fallow at either PD. Genotyping of overwintering canola/rapeseed under field conditions identified nine accessions that survived at both locations, which also had excellent freezing tolerance under controlled conditions. These accessions are good candidates for improving freezing tolerance in commercial canola cultivars.

A field experiment was conducted during the kharif and rabi season of 2016-17 and 2017-18 in the Research farm of College of Agriculture, Central Agricultural University, Imphal in order to study the residual effect of different weed and nutrient management on the productivity and economics of zero tilled rapeseed in rice-rapeseed cropping sequence. The experiment was laid out in factorial randomized block design (FRBD) replicated thrice. The pooled data revealed that among the weed management practices, application of Pyrazosulfuron ethyl (PSE) + Hand weeding (HW) at 40 DAS (W2) and Pyrazosulfuron ethyl (PSE) + Mechanical weeding (MW) at 40 DAS (W3) in preceding kharif rice gave the highest growth and yield of rapeseed. Among the nutrient management practices, better growth and yield of rapeseed were recorded with the application of 50% RDF+ 6t FYM (N1) and 50% RDF+ Azolla (dual crop)@10t/ha + 3t FYM (N2). Maximum gross returns, net returns and B:C ratio were also obtained with the above weed and nutrient management practices.

A two-year field experiment was conducted in 2011 and 2012 at the College of Agriculture and Natural Resources, Shiraz University, Iran to determine the effect of the herbicide trifluralin, mechanical and integrated weed control under different application methods of P fertilizer (midrow banded and surface broadcast) on weed biomass and yield of rapeseed, cultivar Talayeh. Plants grown in unweeded plots at midrow banded and surface broadcast P fertilization methods produced the greatest rapeseed yield (3217 and 1034 kg ha−1, respectively). The increasing effect of P fertilizer on rapeseed yield was less consistent when rapeseed was competing with weeds. It showed that weeds were able to prevent rapeseed from capturing the full benefit of P fertilizer. Trifluralin at 1400 g ha−1 + rotary cultivator + sweep cultivator consistently provided the highest rapeseed grain (2953.5 and 2912 kg ha−1, respectively) and oil yield (1363 and 1320 kg ha−1, respectively). Additionally, trifluralin alone did not provide acceptable full season weed control in rapeseed. Since mechanical weed control implements such as rotary and sweep cultivators are available and inexpensive to Iranian farmers, trifluralin at 1400 g ha−1 + rotary cultivator + sweep cultivator is recommended to improve weed control in rapeseed.

A field experiment was conducted during 2015–16 and 2016–17 at Agriculture Farm, Institute of Agriculture, Visva-Bharati, Sriniketan, West Bengal to study the effect of tillage and weed management practices on weed growth and productivity of yellow mustard in direct-seeded rice-yellow mustard-greengram cropping system. The experiment was laid out in a strip plot design with four horizontal tillage strips and three vertical weed management strips replicated thrice. Results revealed that conservational tillage (zero tillage + residue) along with recommended herbicide (RH) (pendimethalin at 0.75 kg/ha) + one hand weeding (HW) recorded the lower values of total weed density (6.20 and 6.43 no/m2) and dry weight (1.22 and 1.42 g/m2) and higher values of seed yield (1.20 and 1.46 t/ha) in first and second year, respectively. In second year, conservational tillage even with RH alone registered at par values of total weed density and dry weight with conventional tillage + RH + 1 HW and it also recorded 10.2% higher seed yield than conventional tillage + RH + 1 HW. Thus, conservation tillage along with recommended herbicide alone in yellow mustard appeared to be a promising technique with respect to weed suppression and productivity of yellow mustard in conservation agriculture based rice-mustard sarson-greengram cropping system.

No abstract

We used laboratory and field feeding trials to investigate adult carabid beetle preferences for three brassicaceous weed species (rapeseed, wild mustard, and field pennycress) that are pests in canola. All carabid species preferred seeds of rapeseed most and those of field pennycress least and showed intermediate preference for wild mustard seeds. Beetles highly preferred imbibed seeds of all three weed species. Activity–density of carabids and mean weed seed removal were highly correlated in field plots of canola, with activity–density accounting for 67% of the observed variation in seed removal. Our study indicates that seed consumption among carabids is influenced by several factors, including weed species, physiological state of seeds, and carabid activity–density. Carabid seed predation is significant in canola agroecosystems; therefore, understanding these influences has implications for ecological weed management.

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Abstract Poor soil properties and low soil moisture content (SMC) are major limitations for cultivating a second crop after the rainy season rice ( Oryza sativa L.) in the uplands of the Eastern Himalayas. Information on impact of conservation tillage and residue management (RM) to alleviate soil constraints is limited in the region. Thus, a field study was conducted in a rice–rapeseed ( Brassica campestris Var. Toria) system under rainfed conditions with two tillage systems (CsT—conservation and CT—conventional) and five RM practices (100% NPK fertilizer, 50% NPK; 50% NPK + in‐situ rice residue retention [ISRR, 5 Mg ha −1 ], 50% NPK + weed biomass [WB, 10 Mg ha −1 ] fresh weight basis (FW)]; 50% NPK + green manuring [GM, 10 Mg ha −1 FW]), and their impact on soil quality parameters were assessed after 3 years. Significantly lower bulk density and penetration resistance (0–15 cm) and higher water infiltration rate were recorded under CsT than CT. The soil water holding capacity (WHC) and SMC in rapeseed were significantly higher under CsT than those under CT at 0–15 cm and 15–30 cm depths. The WHC and SMC were the maximum under 50% NPK + GM/WB and the minimum under sole application of 50% NPK. After 3 years, there were 5.7% higher available nitrogen (N), 7.3% phosphorus (P), and 3% potassium (K) (kg ha −1 ) in 0–15 cm depth under CsT than those under CT, respectively. Similarly, SOC stock (0–30 cm), soil microbial biomass carbon (SMBC), and dehydrogenase activity (DHA) under CsT were significantly higher than CT. Application of 50% NPK + WB/GM/ISRR registered significantly higher available NPK, SMBC, and DHA in soil than those under 50% and 100% NPK. Thus, CsT along with 50% NPK + WB/GM/ISRR are recommended for improving soil properties under the rice–rapeseed system of the region.

A yield gap analysis for rapeseed (Brassica napus L.) is critical to meeting the oil demand by identifying yield potential and yield constraints. In this study, potential yield (Yp), attainable yield (Yatt), and actual yield (Yact) for winter rapeseed were determined in five different zones of China. A boundary line approach was adopted to calculate Yp, based on a large-scale field experimental database. A meta-analysis was conducted on the data obtained from 118 published studies to evaluate the effects of agronomic factors on rapeseed yield. The main results indicated that farmers only achieved 37–56% of the yield potential across the zones. The low altitude areas (L-URY) and lower reaches (LRY) of the Yangtze River Basin (YRB), China had high yield levels. The total yield gap was 1893 kg ha–1, due to the agronomic management factors, environmental factors, and socioeconomic factors. The meta-analysis showed that weed control and drainage were the best management practices to improve yields (45.6 and 35.3%, respectively), and other practices improved yields by 17.1–21.6%. Consequently, to narrow the yield gap over the short term, the study could focus on techniques that are easily implemented to farmers.

Using crops to control invasive weeds is an important approach for the long-term management of invasive species in agroecosystems. Nitrogen application can improve the yield and quality of crops, but may shift interactions of invasive weeds and crops, potentially affecting grass control ability. To explore the yield of a crop and its control efficacy of invasive weed under different nitrogen conditions, we studied the competitive effects of the high-value crop rapeseed (Brassica napus L.) on growth and photosynthetic characteristics of invasive species littleseed canarygrass in the field experiments. The results showed that the rapeseed yield and its control efficacy on littleseed canarygrass were significantly affected (p &lt; 0.05) under different N regimes, and the control efficacy of littleseed canarygrass by rapeseed increased first and then decreased with the increase of basal nitrogen rates, while increasing topdressing N rates increased control efficacy of littleseed canarygrass by rapeseed. In fact, yield and weed control efficacy of rapeseed was most ideal when both basal and topdressing N was 90 kg·ha−1. We also found that N significantly impacted the competitive ability of rapeseed toward littleseed canarygrass, and rapeseed had the highest competitive ability when both basal and topdressing N was 90 kg·ha−1. With the increase of basal nitrogen rates, competitive balance index (CB) of rapeseed increased initially but decreased beyond an optimal level. CB continually increased with increasing topdressing N rates. Our research also showed level and period of N application had a significant effect (p &lt; 0.01) on the photosynthetic rate (Pn) and chlorophyll content (Chl) of both rapeseed and littleseed canarygrass. Under the same N application regime, the Pn and Chl of littleseed canarygrass were higher than that of rapeseed in December, while the Pn and Chl of rapeseed was higher than that of littleseed canarygrass in February. Our study indicated that photosynthetic characteristics of rapeseed and littleseed canarygrass in different growth stages differ in their sensitivity to N regimes, creating a dynamic competitive relationship. Together, our results demonstrated that optimal application of fertilizer N could help rapeseed produce higher yields and greater weed control efficacy, suggesting that future modeling or experimental studies on utilizing crops to control invasive weeds should carefully consider both timing and placement of N.

Because cropping systems can greatly affect the establishment and spread of alien species populations, the design of cropping systems to control invasive weeds is an important approach for invasive species management in agro-ecosystems to avoid excessive increases in other control measures such as herbicides. The annual weed Phalaris minor Retz. (P. minor) is one of the most troublesome invasive weed species of winter crops in Yunnan Province, China, but the development of cropping systems for ecological control of this weed have received limited research attention. Here, we studied seed dormancy, germination characteristics and reproductive responses of P. minor to various cropping systems to show how cropping systems could be better designed to control P. minor in China. Our research showed that cropping systems significantly affected seed dormancy in submerged paddy fields. Phalaris minor seed remained dormant and the germination rates (less than 10%) were significantly lower (p &lt; 0.05) than in maize fields and dry, bare soil conditions. Wheat, faba bean and rapeseed crops had no significant influence (p &lt; 0.05) on the seed germination rate of P. minor, but increasing soil depth significantly decreased (p &lt; 0.05) the germination rate and germination index of this weed. Total biomass, spike biomass, spike number and seed number of P. minor were significantly reduced (p &lt; 0.05) with increasing proportions of the three crops (wheat, faba bean and rapeseed), with rapeseed having the strongest inhibition effects among the three crops. The reproductive allocation and reproductive investment of P. minor were also significantly reduced (p &lt; 0.05) in mixed culture with wheat and rapeseed. With increasing proportions of wheat or rapeseed, the specific leaf area of P. minor significantly increased (p &lt; 0.05), but the reverse was true for leaf area and specific leaf weight. Moreover, the net photosynthetic rate, stomatal conductance and transpiration rate for P. minor also decreased significantly (p &lt; 0.05) when grown with wheat or rapeseed. These results suggest that optimal cropping systems design could involve planting rapeseed in conjunction with deep plowing and planting rice (continuous submergence underwater) in summer. Such a system could reduce the field populations and seed bank of P. minor, thus providing a sustainable and environmentally friendly means of suppressing P. minor.

No abstract

The application of herbicides is the most effective strategy for weed control and the development of herbicide-resistant crops will facilitate the weed management. The acetolactate synthase-inhibiting herbicide, tribenuron-methyl (TBM), is broadly used for weed control. However, its application in rapeseed field is restricted since rapeseed is sensitive to TBM. Herein, an integrated study of cytological, physiological and proteomic analysis of the TBM-resistant rapeseed mutant M342 and its wild-type (WT) plants was conducted. After TBM spraying, M342 showed improved tolerance to TBM, and proteins implicated in non-target-site resistance (NTSR) to herbicides had a significantly higher level in M342 as compared with the WT. Differentially accumulated proteins (DAPs) between these two genotypes were enriched in glutathione metabolism and oxidoreduction coenzyme metabolic process, which protected the mutant from oxidative stress triggered by TBM. Important DAPs related to stress or defence response were up-accumulated in M342 regardless of the TBM treatment, which might serve as the constitutive part of NTSR to TBM. These results provide new clues for further exploration of the NTSR mechanism in plants and establish a theoretical basis for the development of herbicide-resistant crops.

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A field experiment was conducted during the winter season of 2001-2002 at Mangalpur, Chitwan, Nepal to evaluate the performance of rapeseed in different agronomic management practices. The experiment was conducted with 16 treatments in a randomized complete block design (RCBD) with three replications. The treatments included control without input and four agronomic inputs (NPK, FYM, micronutrient- Zn, B and S and weeding), six and four combinations of two and three inputs respectively and a full package with all inputs. Application of NPK fertilizers increased leaf area and total dry matter per plant significantly as compared to control and weeding practice at 55 and 40 DAS, respectively. Further, in two factor combinations, significantly higher leaf area and particularly total dry matter per plant was produced by the application of NPK fertilizers with FYM at all stages (25 to 85 DAS) of growth and development. Finally, exclusion of NPK fertilizers in the combination of three agronomic inputs significantly lowered leaf area and total dry matter per plant as compared to others which included it at 40 and 70 DAS. All above mentioned trends were reflected on rapeseed yield indicating its significant correlation with leaf area (r=0.971) and total dry matter per plant (r=0.976). In general, addition of NPK fertilizers to other combinations of agronomic inputs increased leaf area and total dry matter per plant significantly. &#x0D; &#x0D; Key words: Leaf area, dry matter, agronomic inputs, yield&#x0D; &#x0D; J. Inst. Agric. Anim. Sci. 26:51-55 (2005)

One of the agronomic methods in weeds management is to recognize cultivars possessing high competitive ability with weeds and to recognize the effective characters in order to breed competitive cultivars in weeds sustainable management. Cultivar identification and discrimination has become an important issue in rapeseed breeding programs. A field experiment was carried out at the research station of Islamic Azad University of Firoozabad, Iran in the 2009 to 2010 growing season. The experiment was conducted using split-plot arrangements in a randomized complete block design with three replications. The treatments included two levels of weed (W0: weed free, and W1: weedy) as main plots and eight rapeseed cultivars (Modena, Okapi, Sarigol, Licord, Hyola308, Zarfam, RGS003 and SLM046) as sub-plots. Ten plant samples were chosen from the middle part of each row and days from emergence to flowering, days from emergence to physiological maturity, plant height, pod length, pods on main stem, pods per plant, seeds per pod, 1000-grain weight, harvest index and grain yield were determined. The ANOVA results show that weeds resulted in reduction of all traits except pod length. In this investigation, the highest and lowest grain yield in weed free condition was seen in Modena and Okapi, respectively while, the highest and lowest grain yield in weedy condition was seen in Sarigol and Hyola308, respectively. Based on the results of grain yield reduction, ability to withstand competition (AWC) index and cluster analysis, Sarigol cultivar, which had high grain yield in both weed free and weedy conditions, was the best cultivar that has competitive ability with weeds and Hyola308 cultivar was the worst. 1000-grain weight was also the best trait to evaluate cultivars that has competitive ability with weeds for grain yield improvement.

Rapeseed (Brassica napus L.) contains allelochemicals that reduces the germination and growth of weed species. An in-vitro experiment was carried out to investigate the effects of different concentrationsof B. napus(L.) water extracts from leaves, stems, roots and flowers on the seed germination and seedling growth of Phalaris minor (Retz.), Convolvulus arvensis (L.) and Sorghum halepense (L.) weeds. All treatments significantly inhibited seed germination, root length, fresh root weight, shoot length and fresh shoot weight of all weed species over the control. The inhibitory effects were concentration dependent. Flower and stem water extracts were most inhibitory to seed germination and root length of all weed species. This work highlighted the allelopathic potential of B. napus extracts for the management of weeds.

Herbicide-resistant cultivars account for over 90% of the canola grown in western Canada and cultivars resistant to glyphosate dominate the market. Field experiments were conducted at three locations in Alberta to compare the glyphosate system with more traditional herbicide regimes. Glyphosate applied before seeding in spring resulted in better weed control, lower dockage, and higher canola yield and net return than 2,4-D applied in the fall. Glyphosate applied once (two- to four-leaf canola) or twice (two- to four-leaf followed by five- to six-leaf canola) in-crop provided similar weed control, dockage, and canola yield as ethalfluralin applied PRE in the fall followed by an in-crop mixture of sethoxydim, ethametsulfuron, and clopyralid; and superior weed control and canola yield and lower dockage than ethalfluralin alone or an in-crop mixture of sethoxydim and ethametsulfuron. The in-crop glyphosate applications resulted in higher net revenues than the other treatments. There was little or no advantage to applying glyphosate twice compared with once in-crop. The amount of active ingredient entering the environment varied with the herbicide regime but was lower with the glyphosate system than with most of the traditional regimes, especially when glyphosate was applied only once in-crop.

Summary An expérimental procedure was designed to provide a simple model for types of analyses necessary to determine weed density thresholds for advantageous use of crop plants engineered for herbicide resistance. Oilseed rape ( Brassica napus L., cv. Tower) biotypes resistant (RES) and susceptible (SUS) to atrazine were used as model crop plants, and wild oat ( Avena fatua L.) was used as the model weed. Along a wild oat density gradient equivalent to 0–128 plants m −2 , RES plants consistently experienced biomass and yield reductions of approximately 10–20% compared to SUS plants. When atrazine was applied at 1.5 kg ha −1 to control wild oats competing with RES plants, RES biomasses and yields were stabilized at the same level as that where 25–30 wild oats m −2 reduce yields of SUS plants. This implies that with wild oat densities of 25–30 plants m −2 , it becomes agronomically advantageous to crop with RES plants plus atrazine rather than to crop with higher‐yielding SUS plants.

Imidazolinone herbicides, which include imazapyr, imazapic, imazethapyr, imazamox, imazamethabenz and imazaquin, control weeds by inhibiting the enzyme acetohydroxyacid synthase (AHAS), also called acetolactate synthase (ALS). AHAS is a critical enzyme for the biosynthesis of branched-chain amino acids in plants. Several variant AHAS genes conferring imidazolinone tolerance were discovered in plants through mutagenesis and selection, and were used to create imidazolinone-tolerant maize (Zea mays L), wheat (Triticum aestivum L), rice (Oryza sativa L), oilseed rape (Brassica napus L) and sunflower (Helianthus annuus L). These crops were developed using conventional breeding methods and commercialized as Clearfield* crops from 1992 to the present. Imidazolinone herbicides control a broad spectrum of grass and broadleaf weeds in imidazolinone-tolerant crops, including weeds that are closely related to the crop itself and some key parasitic weeds. Imidazolinone-tolerant crops may also prevent rotational crop injury and injury caused by interaction between AHAS-inhibiting herbicides and insecticides. A single target-site mutation in the AHAS gene may confer tolerance to AHAS-inhibiting herbicides, so that it is technically possible to develop the imidazolinone-tolerance trait in many crops. Activities are currently directed toward the continued improvement of imidazolinone tolerance and development of new Clearfield* crops. Management of herbicide-resistant weeds and gene flow from crops to weeds are issues that must be considered with the development of any herbicide-resistant crop. Thus extensive stewardship programs have been developed to address these issues for Clearfield* crops.

Field studies were conducted to evaluate weed control in herbicide-resistant canola in Georgia. The resistant canola cultivars and respective herbicides were ‘Pioneer 45A76’ and imazamox, ‘Hyola 357RR’ and glyphosate, and ‘2573 Invigor’ and glufosinate. Weed seed of Italian ryegrass and wild radish were sown simultaneously in October with canola and control of these species was evaluated along with other naturally occurring weeds. Herbicide treatments for the respective herbicide-resistant canola cultivar were imazamox at 0.035 and 0.071 kg ai/ha, glyphosate at 0.84 and 1.64 kg ae/ha, and glufosinate at 0.5 and 1.0 kg ai/ha. Herbicides were applied at one– two-leaf (LF) and three–four-LF canola stages. There was no significant injury to any canola cultivar as a result of herbicide rate or timing of application. By midseason (February), imazamox effectively controlled wild radish, henbit, and shepherd's-purse at both rates and at both timings. When applied to three–four-LF canola, the higher rates of glyphosate and glufosinate were required to provide 75% or greater control of Italian ryegrass, wild garlic, and henbit. Glufosinate did not adequately control wild radish at either rate or application timing. Greenhouse experiments provided similar results.

Herbicide-resistant canola (Brassica napus) is widely cultivated in western Canada. Data from a multi-year field experiment conducted at three locations in Alberta were used to investigate the effect of canola cultivar, time of seeding, polymer seed coating (PSC) on profitability and the net return risk. Cultivars included hybrid and open pollinated. Time of seeding was early and late fall, and early and normal spring. The hybrid canola generally had higher mean net return than the open-pollinated cultivar. The probability of thin canola stand was higher for fall dormant seeding compared with spring seeding. The use of PSC for early fall dormant seeding reduced the likelihood of thin canola stand, which translated into risk-efficient decision. However, PSC use for late fall seeding had mixed results. Early and normal spring seeding was generally risk-efficient at all locations. In exceptional cases, net returns from late fall dormant seeding (with or without PSC) were similar to that of spring seeding. Re-seeding of fall seeded canola in the spring could be beneficial, if the plant density was below 20 plant m -2 . Seeding decisions were robust across a wide range of canola prices, based on the probability of negative net returns. Key words: Canola, fall seeding, net returns, polymer seed coat, re-seeding, risk

To enhance rapeseed germplasm and improve rapeseed variety with resistance to tribenuron- methyl,seeds of Zhongshuang 9( Brassica napus) were treated with 0. 4%,0. 8%,1. 0% and 1. 2% of EMS( ethyl methansulfonate) solution respectively. Results showed that( 1) 1. 0% of EMS was optional for mutagenesis and the phenotype variation in four M2populations were 11. 26%,14. 82%,27. 19% and 12. 38% respectively.( 2) Different concentrations of EMS had different effects on organs.( 3) Three mutants with resistance to tribenuron-methyl were with mutation frequency about 0. 000 1. The M2mutant library,including mutants of cotyledons,leaves,flowers,plant- types,siliques,was available for genetic studies and breeding in rapeseed.

Cropping systems in the northern Great Plains (NGP) have evolved from wheat (Triticum aestivum L.)–fallow rotations to diversified cropping sequences. Diversification and continuous cropping have largely been a consequence of soil moisture saved through the adoption of conservation tillage. Consequently, weed communities have changed and, in some cases, become resistant to commonly used herbicides, thus increasing the complexity of managing weeds. The sustainability of diverse reduced tillage systems in the NGP depends on the development of economical and effective weed management systems. Utilizing the principle of varying selection pressure to keep weed communities off balance has reduced weed densities, minimized crop yield losses, and inhibited adverse community changes toward difficult‐to‐control species. Varied selection pressure was best achieved with a diverse cropping system where crop seeding date, perennation, and species and herbicide mode of action and use pattern were inherently varied. Novel approaches to cropping systems, including balancing rotations between cereal and broadleaf crops, reducing herbicide inputs, organic production, fall‐seeded dormant canola ( Brassica napus and B. rapa ), and the use of cover crops and perennial forages, are discussed in light of potential systems‐level benefits for weed management.

Flax is in the process of development as a crop for bio-industrial and nutraceutical products predicated on the use of genetic modification. Before genetically modified (GM) flax is commercially released, effective management practices should be developed to minimize adventitious presence (AP) of GM volunteer flax in subsequent crops. Field research was conducted at four locations during 2007 and 2008 in central Alberta to quantify and mitigate AP of volunteer flax in glufosinate-resistant (GR) and imidazolinone-resistant (IR) canola. A single preplant application of glyphosate at 1,250 g ae ha −1 in GR canola reduced volunteer flax density from 54 to 3 plants m −2 and seed production from 5,963 to 233 seeds m −2 . Similarly, the recommended rate of POST glufosinate (600 g ai ha −1 ) alone effectively controlled volunteer flax and reduced flax seed viability to &lt; 8% and AP to 0.2%. A combination of preplant (glyphosate) and POST (glufosinate) at recommended rates reduced volunteer flax seed production, yield, and AP to near zero in GR canola. Glyphosate applied preplant was equally effective in IR canola, reducing volunteer flax density from 56 to 2 plants m −2 , and seed production from 5,571 to 472 seeds m −2 . Imazamox + imazethapyr applied POST at all the rates poorly controlled volunteer flax and, even in combination with preplant glyphosate, cannot be recommended for control of flax volunteers in IR canola.

Abstract Chemical‐induced male sterility ( CIMS ) is a method for hybrid rapeseed ( Brassica napus L.) production. Some sulphonylurea herbicides such as tribenuron‐methyl ( TBM ) are used as chemical hybridization agents ( CHA s) in CIMS systems. However, the male parents must be protected from herbicide injury with a shield during spraying of the female parents with CHA s to induce male sterility. Thus, using herbicide‐resistant rapeseed lines as the male parents can significantly simplify the seed production procedure and reduce the cost in hybrid seed production. A rice cytochrome P450 hydroxylase, Os CYP 81A6, has been previously characterized to confer resistance to bentazon and sulphonylurea herbicides. We demonstrate here that the introduction of Os CYP 81A6 renders rapeseed plants resistant to TBM . Compared with wild‐type plants, the transgenic plants displayed normal stamen development and male fertility when treated with 0.05 mg/l of TBM , the dose used for inducing male sterility in hybrid seed production. These results indicate that the Os CYP 81A6 ‐expressing rapeseed plants can be used as the male parents for hybrid rapeseed production using CIMS .

Base editor technology that enables precise base-editing has been developed by employing Cas9 nickase (nCas9) or deactivated Cas9 (dCas9) fused to an enzyme with base conversion activity, named cytidine-deaminase-mediated base editor (CBE, C•G to T•A) or adenine-deaminase-mediated base editor (ABE, A•T to G•C) (Gaudelli et al., 2017; Komor et al., 2016). The base editor systems have been successfully applied in several plant species, including Arabidopsis, rice, wheat, maize, tomato and cotton (Mao et al., 2019). However, it is not clear whether base editing will work in allotetraploid oilseed rape (Brassica napus), one of the world’s most important oil crops. As weeds are a major threat to oilseed rape production, cultivation of herbicide-tolerant varieties is the most cost-effective tool to manage weeds. Acetolactate synthase (ALS), a key enzyme for the biosynthesis of branched-chain amino acids, is the target site of several important herbicides (Powles and Yu, 2010). ALS harboring point mutations could confer sufficient tolerance to herbicidal ALS inhibitors. In this study, we report an efficient CBE system that was employed to create herbicide-resistant B. napus by generating a precisely edited BnALS genes. Based on the released B. napus genome information, cultivars Darmor-bzh (Chalhoub et al., 2014) and ZS11 (Sun et al., 2017) both contain five BnALS copies (Figure 1a). Phylogenetic analysis was performed to reveal the evolutionary relationships among the BnALS copies. It showed that BnALS1 and BnALS3 are highly conserved, exhibiting 92.8% amino acid sequence homology with Arabidopsis ALS (Figure 1a). In contrast, BnALS2, BnALS4 and BnALS5 were distantly related to AtALS, suggesting that they may have undergone subfunctionalization after gene duplication (Figure 1a). Transcriptome data indicated that BnALS1 and BnALS3 were constitutively expressed in all tissues of B. napus, while BnALS4 and BnALS5 were not expressed in all tissues. BnALS2 was expressed only in the ovary and in the seeds at 14 days after flowering (Figure 1b). Taken together, the above results indicate that BnALS1 and BnALS3 are likely have essential ALS housekeeping functions, as indicated in previous studies (Ouellet et al., 1992); this suggests that BnALS1 and BnALS3 are ideal herbicide resistance targets for base editing in B. napus. Amino acid substitution at position P197 (numbered according to the corresponding sequence of A. thaliana) endows various plants with resistance to herbicides, such as tribenuron-methyl (Chen et al., 2017). We therefore selected this region as the target site for creating herbicide-resistant oilseed rape by converting C to T at codon P197 of both BnALS1 and BnALS3 using a CBE system (Figure 1c). This sgRNA also targets BnALS2. The CBE vector used in this study contains a hygromycin phosphotransferase (HPT) selection marker, sgRNA transcription, rat cytidine deaminase (rAPOBEC1), D10A Cas9 nickase (nCas9) and a uracil glycosylase inhibitor (UGI) (Figure 1d). sgRNA transcription was driven by the Arabidopsis U6 promoter, and the cassette rAPOBEC1-nCas9-UGI was amplified from the pnCas9-PBE plasmid (Addgene: #98164) and driven by the Arabidopsis ubiquitin 1 promoter. The construct was transformed into the pure B. napus line J9712 using the Agrobacterium tumefaciens-mediated hypocotyl method, generating 230 independent T0 plants. From PCR analysis using vector-specific primers, 217 (94.3%) independent plants were positive transformants harboring T-DNA insertions. We amplified the target regions of BnALS1-3 by PCR using gene-specific primers and subjected the PCR products to Sanger sequencing. Based on the sequencing results, 7 (3.2%) of the 217 T0 plants exhibited editing events that produced superimposed sequencing chromatograms in the target site of BnALS1 (Figure 1e). However, we could not find any mutations in the target region of BnALS2 or BnALS3. For the BnALS1 target, four plants (#10, #127, #130 and #144) had C–T substitutions at positions 5-7 of the protospacer (scoring PAM as position 21-23); the remaining three plants (#7, #8 and #34) had indels (Figure 1e). Plants #10, #127 and #130 had two C–T substitutions in the target site, but only one edited allele encoded a different amino acid (P197S, Figure 1f). Plant #144 harbored three C–T substitutions in the target site, resulting in a P197F amino acid substitution (Figure 1f). TA cloning and sequencing results further confirmed the editing events, showing that #7, #8 and #34 carried 12, 12 and 11 base pair deletions, respectively (Figure 1e). Both the sequencing chromatograms of the PCR product and the TA cloning results indicated that all mutant lines were heterozygous (Figure 1e,f). The base-editing efficiency for BnALS1 was approximately 1.8% (4/217). To evaluate the possible off-target potential in the present study, a total of 14 putative off-target sites were predicted using the CRISPR-P version 2.0 program (Liu et al., 2017). Sequencing of all these predicted potential off-target sites for the four base-editing mutations did not reveal any editing events. To obtain stable homozygous mutants and test whether the base-editing mutants are inherited, plant #10 were self-pollinated, and individual T1 progeny were genotyped via sequencing of the PCR products of the BnALS1 target site. A total of 42 wild-type plants (WT), 76 heterozygous mutants and 56 homozygous mutants were detected in the T1 progeny (Figure 1g), which indicated that the allelic mutation was successfully transmitted to the T1 generation, with an expected 1:2:1 monogenic segregation pattern (χ2 = 5.03, P > 0.05). Moreover, 16 homozygous mutants without exogenous T-DNA could be obtained in the T1 generation (Figure 1g). However, we still could not find any new editing events in the target region of BnALS2 and BnALS3 in the T1 generation. To determine whether the base-editing mutants can confer oilseed rape with herbicide resistance, P197S mutants and WT (3 plants per genotype) were sprayed with various concentration of tribenuron-methyl (Ryan Pingan, Henan, China, 20 mL/plant) at the 5-6 leaf stage. Twenty days after the treatment, WT was severely damaged, even at a very low concentration (2.5 mg ai/L), whereas the heterozygous and homozygous mutants showed no symptoms of herbicide injury when the dosages were increased to 10 and 15 mg ai/L, respectively (Figure 1h). Strikingly, the homozygotes can even survive at the dosage of 30 mg ai/L, displaying a higher level of herbicide resistance than the heterozygotes (Figure 1h). Further spraying 10 mg ai/L tribenuron-methyl (three times the field-recommended dose) on more plants confirmed the herbicide resistance of the P197S mutants (Figure 1i). In addition, to easily discriminate between the WT and P197S mutant alleles, allele-specific PCR markers were developed. The forward primer was BnALS1 specific and could distinguish between BnALS1 and other homologous genes. While the target site was chosen to design the reverse primers, the 3’ end corresponded to the two base-editing sites (Figure 1j). Moreover, one additional mismatched base was introduced into the reverse primer for the WT genotype immediately in front of the two SNP sites to reduce nonspecific amplification (Figure 1j). Thus, both gene specificity and allele specificity were successfully obtained, and the approach was sufficiently robust to easily discriminate among the WT, heterozygous and homozygous mutants (Figure 1j). In summary, we successfully established a base-editing system that can efficiently introduce C to T conversion in sgRNA targets in oilseed rape. The CBE would be a very useful tool for gene function studies and precision molecular breeding in oilseed rape. Moreover, the BnALS1 gene was precisely edited at position P197 by CBE system, conferring tribenuron-methyl resistance to oilseed rape. The P197S substitution in BnALS1 generates a novel herbicide-resistant mutant in oilseed rape, and the transgene-free homozygous mutant with its allele-specific markers can be used for breeding herbicide resistance and thus might facilitate weed management in oilseed rape production. This work was supported by the National Key Research and Development Program of China (2016YFD0101000, 2016YFD0102000), the National Science and Technology Major Project (2018ZX08020001), the National Science Foundation of Jiangsu Province (BE2018356). The authors declare no competing interests. Y.W. and H.Z. conceived the study; J.W., C.C., G.X., D.L., L.L. and S.Y. performed the experiments; J.W. wrote the manuscript; Q.S. and Y.F. revised the manuscript.

OAC Triton is the first licensed, triazine-resistant spring rapeseed (Brassica napus L.). It produces seed low in erucic acid and glucosinolate content. Yield levels have averaged approximately 80% of Regent and oil content has averaged 2.4% less than Regent. OAC Triton is expected to be used where rapeseed production is restricted or inhibited by serious cruciferous weed infestations, other triazine-susceptible weed problems, or by atrazine herbicide residues.Key words: Rapeseed, triazine-resistant, Brassica napus L., canola, cultivar description

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The seeds of Swietenia mahagoni L. (Meliaceae) have been used as a traditional medicine for a long time. However, there is no report on its allelopathic activity. Considering allelopathy as an ecologically sound weed management approach, the aqueous methanol extracts of S. mahagoni seeds were examined on seedling growth of four dicotyledonous plants; cress, alfalfa, rapeseed, lettuce, and three monocotyledonous plants; barnyard grass, timothy and foxtail fescue at six concentrations (0.001, 0.003, 0.01, 0.03, 0.1 and 0.3 g dry weight (DW) equivalent extract/mL). The powder of S. mahagoni seeds was extracted with aqueous methanol, filtered and evaporated completely. The crude extract was then diluted with methanol to prepare six concentrations. The seeds of test plants were incubated for 48 h and the shoot and root length was measured. The suppression activity of S. mahagoni seed extracts was concentration-dependent and species-specific. For 50% inhibition (I 50 ) of shoot and root growth of monocotyledonous plants, the required concentrations ranged from 0.0433-0.1443 and 0.0007-0.0348 g DW equivalent extract/mL, respectively. In case of dicotyledonous plants, I 50 values for the growth of shoot and root ranged from 0.0040-0.1077 and 0.0010-0.0248 g DW equivalent extract/mL, respectively. Considering I 50 values, the shoot growth of cress and the root growth of barnyard grass were the most sensitive, whereas foxtail fescue is found the least sensitive to the seed extracts of S. mahagoni. These findings suggest that the seed extracts of S. mahagoni may possess growth inhibitory substances and; therefore, might have possibility to be used in the biological weed management option.

Field experiments were conducted over a number of years to determine the effectiveness for Canada thistle (Cirsium arvense (L.) Scop.) control and tolerance of rapeseed (Brassica campestris L. and Brassica napus L.) to various rates of dicamba (0–140 g/ha) and picloram (0–110 g/ha). Dicamba at 70 g/ha and picloram at 20 g/ha provided about 60% and 50%, respectively, reduction in the dry weight of shoots of Canada thistle growing in Candle rapeseed. This degree of suppression did not result in increases in rapeseed yield over the untreated check. Flower formation in Canada thistle was prevented by all rates of dicamba and picloram tested. In tolerance experiments the yield of Candle rapeseed was not reduced with dicamba applied at rates up to 70 g/ha at the two-, four- or six-leaf stages, but yields were reduced at higher rates. Picloram applied at rates up to 70 g/ha did not reduce the yield of Candle rapeseed. Altex yields were reduced with 40 g/ha and higher rates and Regent yields were reduced with picloram applied at 70 g/ha at the six-leaf stage. The data indicate that dicamba at 70 g/ha and picloram at 20 g/ha may selectively suppress the growth of Canada thistle in rapeseed and reduce the spread of this weed through seed or vegetative means while maintaining some rapeseed yield from the treated areas of a field.Key words: Canada thistle control, canola, dicamba, picloram, rapeseed tolerance

Studies of mechanisms of resistance to glyphosate have increased current understanding of herbicide resistance mechanisms. Thus far, single-codon non-synonymous mutations of EPSPS (5-enolypyruvylshikimate-3-phosphate synthase) have been rare and, relative to other herbicide mode of action target-site mutations, unconventionally weak in magnitude for resistance to glyphosate. However, it is possible that weeds will emerge with non-synonymous mutations of two codons of EPSPS to produce an enzyme endowing greater resistance to glyphosate. Today, target-gene duplication is a common glyphosate resistance mechanism and could become a fundamental process for developing any resistance trait. Based on competition and substrate selectivity studies in several species, rapid vacuole sequestration of glyphosate occurs via a transporter mechanism. Conversely, as the chloroplast requires transporters for uptake of important metabolites, transporters associated with the two plastid membranes may separately, or together, successfully block glyphosate delivery. A model based on finite glyphosate dose and limiting time required for chloroplast loading sets the stage for understanding how uniquely different mechanisms can contribute to overall glyphosate resistance.

The relationships between weeds and insects in canola stands with different seeding rates are not fully understood. Varying seeding rates in canola crops can create different conditions that affect both weed and insect populations and their interactions. The aim of this work was to determine the response of weeds and insects of selected taxa to different densities of canola stand densities and to clarify the interactions between weeds and insects in canola stands. The field experiment was conducted on a plot located in the cadastral area of the municipality of Pěnčín (Moravia, Czech Republic). The results show that a reduced canola sowing rate of oilseed rape leads to increased weed infestation, which is dominated by one taxon (Papaver rhoeas L.). The increase in weed infestation of canola stands is not reflected in an increase in the diversity of captured insects. Increased canola seeding rate improves weed suppression but increases the number of canola pest insects. A higher number of plants and more canola biomass increase the food supply and, thus, make the stand more attractive to canola pests. The taxon Brassicogethes aeneus dominated the pests species spectrum. Changing the seeding rate of canola results in a response in weed and insect populations. The standard recommended seeding rate is optimal in terms of competitive suppression of weeds and the occurrence of pests and trapped insects. Increasing or decreasing the seeding rate of rapeseed does not bring any benefits in terms of pest regulation or biodiversity. However, the results obtained indicate an interesting weed–insect interaction in the conditions of canola stands.

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India is the fourth largest oilseed economy in the world. Among the seven edible oilseeds cultivated in India, rapeseed-mustard contributes 28.6% in the total oilseeds production and ranks second after groundnut sharing 27.8% in the India’s oilseed economy. The mustard growing areas in India are experiencing the vast diversity in the agro climatic conditions and different species of rapeseed-mustard are grown in some or other part of the country. Under marginal resource situation, cultivation of rapeseed-mustard becomes less remunerative to the farmers. This results in a big gap between requirement and production of mustard in India. Therefore site-specific nutrient management through soil-test recommendation based should be adopted to improve upon the existing yield levels obtained at farmers field. Effective management of natural resources, integrated approach to plant-water, nutrient and pest management and extension of rapeseed-mustard cultivation to newer areas under different cropping systems will play a key role in further increasing and stabilizing the productivity and production of rapeseed-mustard. The paper reviews the advances in proper land and seedbed preparation, optimum seed and sowing, planting technique, crop geometry, plant canopy, appropriate cropping system, integrated nutrient management and so forth to meet the ever growing demand of oil in the country and to realize the goal of production of 24 million tonnes of oilseed by 2020 AD through these advanced management techniques.

Concerns about the health and environmental impacts of herbicide use have led farmers and researchers to seek alternative methods of weed management. One such alternative is the use of allelopathic cover crops, which release chemicals into the soil environment that can contribute to weed management through suppression of weed seed germination, seedling emergence and establishment, and seedling growth, in addition to providing other soil quality benefits to farmers. Brassicas, or members of the Brassicaceae, contain glucosinolates, sulfur-containing molecules that degrade to form compounds toxic to a variety of organisms. Glucosinolate content varies between brassicas grown as cover crops; mustards typically have very high glucosinolate content, whereas others, including canola and rapeseed, contain lower amounts. Brassica residues have strong phytotoxic effects; weed density and biomass has been observed to be lower in crops following incorporation of brassica residue. In addition to a literature review, this thesis describes two experiments that investigated the mechanisms behind this observed weed suppression by brassicas. The first experiment examined seedling establishment following incorporation of brassica residues and residues of other short-season cover crops. We hypothesized that all cover crop residues would decrease and delay seedling emergence compared to fallow and that emergence following the brassica residues would be lowest and slowest, particularly following the high-glucosinolate mustard. Based on the theory that smaller seeds are more susceptible to stress such as those imposed by allelopathic cover crops, we expected that smaller-seeded species would be affected more than larger-seeded ones. While average emergence was indeed lower following all of the cover crop residues compared to fallow, emergence was similar following the brassicas and following the other cover crop residues. Seed size was a poor predictor of species emergence following the cover crops. While emergence was slower following all the cover crop residues, emergence rates were generally similar between the brassicas and the other cover crops, although delayed emergence following mustard was observed in one year. The second experiment examined the effects of mustard and canola on the growth of established redroot pigweed and green bean plants and, in turn, on interspecific competition. Redroot pigweed and green bean, both alone and in mixture, were seeded into incorporated mustard and canola residues and fallow plots; plants were sampled throughout the season to assess the effects of the cover crop residues on growth. We hypothesized that growth of the smaller-seeded redroot pigweed would be harmed by the brassica residues, particularly early in the season, but that growth of the larger-seeded green bean would not be affected. In turn, we expected that the brassica residues would mediate interspecific competition, through differential effects on growth, thereby conferring a competitive edge to green bean plants growing with redroot pigweed. As expected, brassica cover crop residues did not affect green bean height, biomass, leaf area, relative growth rate, or final marketable yield. Contrary to expectations, these parameters for redroot pigweed were also unaffected. While the presence of competition reduced growth of both species, no interaction with cover crop residue was found.

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Development of herbicide-resistant crops has resulted in significant changes to agronomic practices, one of which is the adoption of effective, simple, low-risk, crop-production systems with less dependency on tillage and lower energy requirements. Overall, the changes have had a positive environmental effect by reducing soil erosion, the fuel use for tillage, and the number of herbicides with groundwater advisories as well as a slight reduction in the overall environmental impact quotient of herbicide use. However, herbicides exert a high selection pressure on weed populations, and density and diversity of weed communities change over time in response to herbicides and other control practices imposed on them. Repeated and intensive use of herbicides with the same mechanisms of action (MOA; the mechanism in the plant that the herbicide detrimentally affects so that the plant succumbs to the herbicide; e.g., inhibition of an enzyme that is vital to plant growth or the inability of a plant to metabolize the herbicide before it has done damage) can rapidly select for shifts to tolerant, difficult-to-control weeds and the evolution of herbicide-resistant weeds, especially in the absence of the concurrent use of herbicides with different mechanisms of action or the use of mechanical or cultural practices or both.