Mulched cover crops as an alternative to conventional weed management systems in vineyards

Conventional methods of weed management in vineyards rely primarily on herbicides and tillage. The desire to adopt alternatives to these methods is driven by environmental and economic reasons. Weed suppression and grape yield under mulched cover crop systems at two rainfed northern California vineyards were similar to, and at times exceeded, those under conventional tillage or herbicide management. Cover crop productivity was positively correlated with weed suppression and mulch decomposition rates and seemed to be determined primarily by location and then by cover crop type. The mulch from mowed cover crops averaged 603(± 94) gm⁻² at the two sites. Weed suppression was linked to light interception by the mulch cover for most weed species. Subterranean clover planted directly in the vine row significantly reduced weed cover where it established. The increased dominance of the perennial Convolvulus arvensis and reduction of certain annual species was indicative of species compositional changes in all treatments. Profits under the cover cropping systems exceeded those under conventional tillage and herbicide systems by €  794 ha⁻¹ averaged over the duration of the experiment at both locations.     

Current status of biological control of paddy weeds in Vietnam

Rice is a staple food in Vietnam and accounts for > 7.7 × 10⁶ cultivated ha, which provide 35.5 × 10⁶ t of rice, of which 4.2 × 10⁶ t were exported in 2004. The enlargement of the cropping area and the enhancement of rice yield have rapidly increased the amount of agrochemicals, including herbicides, in crop production in Vietnam. From 1990–2003, the percentage of herbicides in total pesticides has increased ≈ 10-fold to 30.2%. In addition, the improper use of herbicides caused environmental hazards, unsafe agricultural products, and human health problems. Biological management integrated with traditional weed control techniques might help to reduce the dependence on synthetic herbicides and build eco-friendly, sustainable agricultural production in Vietnam. This paper reviews the efforts in establishing a strategy for biological management of weeds that was conducted in recent years by Vietnamese weed scientists. This has included cropping system management, water and soil management, integrated pest management, and utilization of plant allelopathy as major components of the strategy. Many plants with strong allelopathic potential can be a source for biological weed suppression and soil fertility improvement. The utilization of allelopathic properties in rice might also help to provide new rice cultivars with weed-suppressing characteristics.     

Effects of crop management practices on Echinochloa crus-galli and Chenopodium album seed production in a maize/soyabean rotation

Seed production of residual weed populations needs to be taken into account when estimating the long-term impact of low-input agronomic practices. The objective of this study was to measure the effects and interactions of crop, weed control, tillage practice and nutrient source on the seed production of the dominant residual weed species in a maize/soyabean rotation at two sites: Echinochloa crus-galli (L.) Beauv. on a Sainte-Rosalie clay and Chenopodium album L. on a Duravin clay loam. Seed production per unit area was estimated in each experimental unit. Weed seed production was greater under mechanical weed control compared with chemical weed control. In 1997, E. crus-galli seed production reached over 326 000 seeds m^–2 in mechanical weed control treatments, but averaged less than 500 seeds m^–2 in the chemical weed control treatments. Chenopodium album produced in the range of 766 000 and 73 000 seeds m^–2 in mechanical and chemical weed control treatments respectively. Very few or no weed seeds were produced in soyabean under chemical control. Tillage intensity and nutrient source did not affect seed production of either weed species, with the exception that E. crus-galli produced more seeds in chisel than in mouldboard plough tillage in soyabean. Weed control method had more impact on seed production than tillage intensity and nutrient source in a maize/soyabean rotation.     

Correlation between the soil seed bank and weed populations in maize fields

Annual weed populations establish every year from persistent seed banks in the soil. This 3 year study investigated the relationship between the number of weed seeds in the soil seed bank and the resultant populations of major broadleaf and grass weeds in 30 maize fields. After planting the crop, 1 m² areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying to a depth of 100 mm and the weed seeds therein were enumerated. The emerged weed seedlings in the field sampling areas were counted over the following 8 weeks. Up to 67 broadleaf species and five grass weeds were identified, although not all were found at every site and some were specific to a region or soil type. For the most abundant weeds in the field plots, on average 2.1–8.2% of the seeds of the broadleaf species and 6.2–11.9% of the seeds of the grass weeds in the soil seed bank emerged in any one year, depending on the species. Overall, the results showed a strong linear relationship between the seed numbers in the soil and the seedling numbers in the field for all the grasses and for most broadleaf weeds. For some species, like Trifolium repens , only a weak relationship was observed. In the case of Chenopodium album , which had the largest seed bank, there was evidence of asymptotic behavior, with seedling emergence leveling off at high seed numbers. An estimate of the soil seed bank combined with knowledge of the germination and behavior of specific weed species would thus have good potential for predicting future weed infestations in maize fields.     

Improved management of Avena ludoviciana and Phalaris paradoxa with more densely sown wheat and less herbicide

Summary The effectiveness of crop competition for better weed control and reducing herbicide rates was determined for Avena ludoviciana and Phalaris paradoxa . Four experiments, previously broadcast with seeds of the two weeds in separate plots, were sown with three wheat densities, and emerged weeds were treated with four herbicide doses (0–100% of recommended rate). The measured crop and weed traits were first analysed across experiments for treatment effects. Grain yield and weed seed production data were then analysed using cubic smoothing splines to model the response surfaces. Although herbicide rate for both weeds and crop density for P. paradoxa had significant linear effects on yield, there was a significant non-linearity of the response surface. Similarly, herbicide rate and crop density had significant linear effects on weed seed production, and there was significant non-linearity of the response surface that differed for the weed species. Maximum crop yield and reduction in seed production of P. paradoxa was achieved with approximately 80 wheat plants m⁻² and weeds treated with 100% herbicide rate. For A. ludoviciana , this was 130 wheat plants m⁻² applied with 75% herbicide rate. Alternatively, these benefits were achieved by increasing crop density to 150 plants m⁻² applied with 50% herbicide rate. At high crop density, application of the 100% herbicide rate tended to reduce yield, particularly with the A. ludoviciana herbicide, and this impacted adversely on the suppression of weed seed production. Thus, more competitive wheat crops have the potential for improving weed control and reducing herbicide rates.     

Influence of straw management, nitrogen fertilization and dosage rates on the dissipation of five sulfonylureas in soil

The dissipation behaviour of metsulfuron-methyl, tribenuron-methyl, thifensulfuron-methyl, triasulfuron and amidosulfuron were studied in soil following post-emergence spring applications to cereal crops. Incorporation or removal of straw and different fertilizer applications had no influence on the disappearance time (DT₅₀) of the herbicides. However, in laboratory trials dissipation of metsulfuron-methyl, triasulfuron and amidosulfuron at higher application rates was accelerated after incorporation of straw into the soil. The addition of straw decreases soil pH thereby causing faster hydrolysis of the compounds. Addition of nitrogen fertilizer increased the half-lives (t_1/2) of the herbicides. Combination of both straw and N fertilizer, however, had no effect. Neither straw nor N influenced the degradation of tribenuron-methyl and thifensulfuron-methyl.
The DT₅₀ of all herbicides investigated varied from 6 to 17 days in the field trials. Except for amidosulfuron, herbicides could not be detected 38–68 days after application. In the laboratory, t_1/2 values were higher than those in the field at 75 days (amidosulfuron), 63 days (metsulfuron-methyl), 35 days (triasulfuron) and 13 days (tribenuron-methyl). Only the t_1/2 of thifensulfuron-methyl was at 29 h faster under laboratory conditions. T_1/2 values of all herbicides were influenced by their initial concentration. The t_1/2 values of amidosulfuron and tribenuron-methyl at 1 mg a.i. kg⁻¹ soil were 2–2.5 times higher than at the recommended field application rate of 42 μg a.i. kg⁻¹ soil.     

Weed control in summer-sown soybeans with flumioxazin plus acetochlor and flumiclorac-pentyl plus clethodim

Field trials were conducted in Taigu, Shanxi province, China, to evaluate the efficacy of flumioxazin plus acetochlor and flumiclorac-pentyl plus clethodim applied to summer-sown soybeans at pre- and postemergence. It was demonstrated that tank-mixing flumioxazin at 50 g ai ha^-1 and acetochlor at 800 g ai ha^-1 created an effective soil-applied herbicide for weed control in soybean crops. The control efficacy was better than when the herbicides were applied individually, and no injury was caused to the soybeans. Flumiclorac-pentyl at 50 g ai ha^-1 plus clethodim at 70 g ai ha^-1 suppressed both broad-leaved weeds and grass weeds with an increased efficacy of more than 90%. Flumiclorac-pentyl applied alone or tank-mixed caused some injury to soybean seedlings, but the soybeans recovered 2–3 weeks after treatment and there was no reduction in the yield.     

Identifying key components of weed beet management using sensitivity analyses of the GeneSys-Beet model in GM sugar beet

Genetically-modified (GM) sugar beet varieties tolerant to non-selective herbicides would be useful for managing weed beet, an annual form of Beta vulgaris impossible to eliminate with herbicides in sugar beet. However, it is highly probable that the herbicide-tolerance transgene would be transmitted to the weed through pollen flow. It is therefore essential to study how weed beet. particularly Herbicide-Tolerant (HT) populations, develop in cropping systems and how to optimise crop succession and management for controlling these weeds. As multiple interactions and long-term effects make field experiments impractical, we carried out a simulation study with a deterministic and mechanistic model, G ene S ys- B eet , which quantifies weed beet dynamics and gene flow in cropping systems with interactions with climate, soil structure and hydro-thermal conditions. The sensitivity analysis consisted of 250 000 random combinations of input variables to rank cropping system components according to their effect on both total and GM weed beet infestations. Frequency of sugar beet crops, crop succession, manual and mechanical weeding and tillage were identified as the most important variables. Several cultivation techniques must be combined to efficiently control weed beet. Our recommendations are complex, but a delayed return of sugar beet in the rotation. Harvest should be followed as soon as possible by a shallow tilling; tillage should always be as shallow and as early as possible, except before sugar beet where mouldboard ploughing is advisable. If possible, sowing dates should be delayed. Sugar beet should be weeded mechanically and/or manually, aiming at late and efficient, rather than early or frequent operations. Herbicides should be applied whenever possible and target all weed beet stages and genotypes. Set-aside must be cut as frequently and as late as possible.     

Minimal soil disturbance combined with spring cropping can halt soil seedbank accumulation of Alopecurus myosuroides

The basic mechanism of soil inversion tillage for control of annual weeds is based on the vertical translocation of weed seeds from the soil surface to deeper soil layers. Buried weed seeds either remain dormant in the soil seedbank and are exposed to biological and chemical decay mechanisms, or they germinate but the seedlings cannot reach the soil surface (fatal germination). However, depending on the seed biology of the respective target species, frequent inversion tillage can lead to a build-up of the soil seedbank. For soil seedbank depletion based on available knowledge of the biology of Alopecurus myosuroides seeds, soil inversion tillage is suggested to be reduced to every third or fourth year with reduced or even no-tillage (direct seeding) in between (rotational inversion tillage systems). Including spring crops in the crop rotation could further help dampening the population growth and hence the seed return into the seedbank. This study investigated the effect of rotational inversion tillage in combination with reduced tillage or direct seeding on the soil seedbank and population development of A. myosuroides. In a long-term field trial, set up in 2012, these tillage strategies were compared with continuous inversion tillage in a 3-year crop rotation with two consecutive years of winter wheat (Triticum aestivum) followed by spring barley (Hordeum vulgare). The results showed a significant decline in the soil seedbank following the spring crop, irrespective of the tillage system. The continuous inversion tillage system and inversion tillage before spring cropping with reduced tillage (shallow tillage with a disc harrow) before winter wheat both led to accumulation of seeds in the soil seedbank. In contrast, inversion tillage before spring cropping with direct seeding of winter wheat depleted the soil seedbank significantly after only one crop rotation. Although only covering one intensively studied field site, these findings highlight the need for diversified cropping systems and indicate potential avenues for reducing soil tillage while controlling economically important weeds.     

Comparison of different weed management systems and their effects on yield of coconut plantations in Sri Lanka

The influence of five different weed management systems on nut yield of coconut were evaluated to determine an economical and effective method of controlling weeds in coconut plantations in the low country, dry zone in Sri Lanka. Treatments imposed included slashing and mulching around the palms with slash (T1), slashing and removing the slash (T2), application of glyphosate (N-(phosphonomethyl)-glycine) alone at 1.44 kg ai ha⁻¹ (T3), application of glyphosate alone at 2.88 kg ai ha⁻¹ (T4) and cover cropping with Pueraria phaseoloides (T5). All treatments were applied twice a year, except for the cover cropping treatment, T5. Based on a reduction in weed biomass, treatments T3, T4 and T5 were found to be significantly effective over other treatments. Coconut yield was increased significantly ( P  < 0.05) in glyphosate-applied plots at both tested rates. Control of weeds with the lower concentration of glyphosate (1.44 kg ai ha⁻¹) resulted in a 25% increase in nut yield over the uncontrolled weed plots. At this rate, it was found to be the most effective and economical method of controlling weeds in coconut plantations. Cover cropping with Pueraria phaseoloides was effective in controlling weeds in the long-term, but was not economical compared with the glyphosate application.     

Development of a spot plow providing complete inversion for effective weed control

Tillage for the "complete inversion" of soil, that is, overturning soil slices 180° was proposed, a "spot plow" was developed and tested to accomplish the task, and a simulation model was evaluated to demonstrate the efficacy of the plow on weed control. A 360 mm wide spot plow was designed to operate at a speed of 1.9 m s⁻¹ for the spot plowing with the least possible lateral displacement of the soil slice by utilizing the inertia of the soil slice and securely rotating it. In field experiments, complete spot inversion required an operating speed of at least 1.6 m s⁻¹; at lower speeds, a portion of the soil block was left half-inverted and further lowering led to considerable lateral displacement. The displacement in the forward and lateral directions was minimal, implying that spot plowing is suitable for potential application to and verification of the weed population dynamics model in the field. A simple linear matrix model of the population dynamics of annual weeds was proposed, whereby four layers of soil were set to describe tillage and other ecological events. The effect of tillage on weed control was evaluated by the equilibrium reproduction rate allowed to sustain a stable population of weeds. The simulation model showed that alternately changing the depth of spot plowing had a significant effect on controlling weeds of low-survival-rate seeds, even when some incomplete inversion of the soil slice was taken into account.     

Comparison of sulfonylurea herbicide residue detection in soil by bioassay, enzyme-linked immunosorbent assay and hplc

The ability of bioassay, enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (hplc) methods to detect sulfonylurea herbicides in soil was evaluated as part of a project studying the leaching and persistence of these herbicides in the alkaline soils of south-eastern Australia. Soil samples with known concentrations between 0.1 and 10 μg a.i. kg⁻¹ chlorsulfuron, metsulfuron-methyl or triasulfuron were prepared by an independent laboratory and supplied in coded bags to separate laboratories for testing. The accuracy of the results was analysed, and the merits of each method are discussed. Bioassay was suitable for measuring biologically active residues from 0.1 to 1.0 μg a.i. kg⁻¹. ELISA accurately measured residues in the range of 0.1–10 μg a.i. kg⁻¹, making it the most widely adaptable assay tested. It will be useful for measuring residues in sodic subsoils where bioassay plants grow poorly. There was good reproducibility between the bioassay and ELISA. The hplc technique used in this study was not as accurate as bioassay or ELISA at quantifying residues of 3.0–10 μg a.i. kg⁻¹ and could not detect residues at or below 1.0 μg a.i. kg⁻¹.     

Weed flora and soil seedbanks in fields dominated by Imperata cylindrica in the moist savannah of West Africa

Imperata cylindrica (L.) Raeuschel is a dominant and infamous grass weed in the savannah of West Africa. Research to reduce the weed to non-damaging levels is a priority activity at many agricultural institutions. The successful development and implementation of long-term I. cylindrica management strategies depend on the ability to predict changes in weed composition after I. cylindrica has been controlled effectively. The weed flora and soil seedbank were assessed from 329 fields dominated by this species in the fringes of the humid forest (HFF), coastal/derived savannah (CDS) and in the southern Guinea savannah (SGS) in 1996 and 1997. The objectives of the study were to correlate species composition of the weed flora with that of the soil seedbank and to determine the effect of management factors and soil properties on the composition of the weed flora. Species richness in the weed flora and in the weed seedbank was higher in the SGS than in the CDS and HFF. Mean weed density per field was generally higher in the HFF (156 ± 25.0 weeds m^–2) than in the CDS (108 ± 8.1 weeds m^–2) and in the SGS (92 ± 6.3 weeds m^–2). Weed composition varied with agroecological zone as well as with management factors and soil properties. Sørenson's index of similarity was low (mean=0.20) in all zones, indicating poor similarity between the weed flora above-ground and the soil seedbank.     

Influence of sowing density and spatial pattern of spring wheat (Triticum aestivum) on the suppression of different weed species

To better understand the potential for improving weed management in cereal crops with increased crop density and spatial uniformity, we conducted field experiments over two years with spring wheat ( Triticum aestivum ) and four weed species: lambsquarters ( Chenopodium album ) , Italian ryegrass ( Lolium multiflorum ), white mustard ( Sinapis alba ), and chickweed ( Stellaria media ). The crops were sown at three densities (204, 449, and 721 seeds m⁻²) and in two spatial patterns (normal rows and a highly uniform pattern), and the weeds were sown in a random pattern at a high density. In most cases, the sown weeds dominated the weed community but, in other cases, naturally occurring weeds were also important. There were strong and significant effects regarding the weed species sown, the crop density, and the spatial distribution on the weed biomass in both years. The weed biomass decreased with increased crop density in 29 out of 30 cases. On average, the weed biomass was lower and the grain yield was higher in the uniform compared to the row pattern in both 2001 and 2002. Despite the differences in weed biomass, the responses of L. multiflorum , S. media , and C. album populations to crop density and spatial uniformity were very similar, as were their effects on the grain yield. Sinapis alba was by far the strongest competitor and it responded somewhat differently. Our results suggest that a combination of increased crop density and a more uniform spatial pattern can contribute to a reduction in weed biomass and yield loss, but the effects are smaller if the weeds are taller than the crop when crop–weed competition becomes intense.     

Less hazardous alternative herbicides to control weeds in immature oil palm

In 2002, the Malaysian government had banned the use of the hazardous herbicide, paraquat. Most growers perceive that paraquat is the most effective herbicide and provides the fastest mode of action to control weeds. An experiment was conducted at MAB Agriculture-Horticulture, Sepang, Selangor, Malaysia, from February 2004 to February 2005 to evaluate the efficacy and ability of the less hazardous herbicides, glufosinate ammonium and glyphosate, as an alternative to the hazardous herbicide, paraquat, in controlling weeds in immature oil palm (<3 years old). The results showed that paraquat needed high rates, 600 and 800 g ha⁻¹, to control weeds effectively. However, lower rates of glufosinate ammonium (200 g ha⁻¹) and glyphosate (400 g ha⁻¹) gave excellent weed control. The results showed that the efficacy of glufosinate ammonium and glyphosate were much better than paraquat. The results also showed that, with no direct contact with the plants, paraquat, glufosinate ammonium, and glyphosate had no adverse effect on the vegetative and generative growth of oil palm in this study. These results proved that the less hazardous herbicides, glufosinate ammonium and glyphosate, could be used as an alternative to paraquat to control weeds in immature oil palm.     

Weed management in conservation crop production systems

Information on weed management in conservation crop production systems is needed as adoption of practices such as reduced tillage and cover crops becomes more widespread. This review summarizes recent research on weed management aspects in these systems. Changes in patterns of tillage, planting systems, and other management strategies can alter the soil environment and lead to shifts in weed populations. Weed patterns and populations are not always consistent and vary with locale, crop, and herbicide use. However, in many long-term conservation management studies, a general increase in perennial weeds and grass species has been observed. The development of low-dose herbicides, selective postemergence herbicides, and transgenic crops has greatly improved the flexibility of producers who use conservation systems where opportunities for tillage are limited. With a higher level of management inputs, producers can successfully implement conservation management practices.     

Strategic tillage in Australian conservation agricultural systems to address soil constraints: How does it impact weed management?

In the conservation agricultural systems practised in Australia, cultivation is not commonly utilised for the purpose of weed control. However, occasional use of tillage (strategic tillage) is implemented every few years for soil amelioration, to address constraints such as acidity, water repellence or soil compaction. Depending on the tillage method, the soil amelioration process buries or disturbs the topsoil. The act of amelioration also changes the soil physical and chemical properties and affects crop growth. While these strategic tillage practices are not usually applied for weed control, they are likely to have an impact on weed seedbank burial, which will in turn affect seed dormancy and seedbank depletion. Strategic tillage impacts on seed burial and soil characteristics will also affect weed emergence, plant survival, competitive ability of weeds against the crop and efficiency of soil applied pre-emergent herbicides. If growers understand the impacts of soil amelioration on weed demography, they can more effectively plan management strategies to apply following the strategic tillage practice. Weed seed burial resulting from a full soil inversion is understood, but for many soil tillage implements, more data is needed on the extent of soil mixing, burial of topsoil and the weed seedbank, physical control of existing weeds and stimulation of emergence following the tillage event. Within the agronomic system, there is no research on optimal timing for a tillage event within the year. There are multiple studies to indicate that strategic tillage can reduce weed density, but in most studies, the weed density increases in subsequent years. This indicates that more research is required on the interaction of amelioration and weed ecology, and optimal weed management strategies following a strategic tillage event to maintain weeds at low densities. However, this review also highlights that, where the impacts of soil amelioration are understood, existing data on weed ecology can be applied to potentially determine impacts of amelioration on weed growth.     

Suppression of weeds and weed seeds in the soil by stubbles and no-tillage in an arid maize-winter wheat-common vetch rotation on the Loess Plateau of China

Reduced tillage provides ecological and economic benefits to arable land on the Loess Plateau of China, where soil erosion has long been a serious problem and soil water availability is largely restricted. However, high abundances of weeds in reduced tillage systems cause significant yield losses. In this study, we explored the effects of no-tillage and stubble retention on the number and density of weeds and weed seeds in a 12-year maize-winter wheat-common vetch rotation on the Loess Plateau. Four treatments including conventional tillage, no-tillage, conventional tillage+stubble retention and no-tillage+stubble retention were designed and applied. We found that no-tillage increased the number of weed species and weed density in most of the crops, while stubble retention decreased weed density in maize and tended to suppress weeds in both no-tillage treatments(no-tillage and no-tillage+stubble retention). No-tillage led to an increase in the number of weed species in the weed seedbank and tended to increase seed density during the spring growth of winter wheat, but it decreased seed density during post-vetch fallow. Stubble retention tended to reduce seed density during the spring growth of winter wheat and post-vetch fallow. We concluded that no-tillage can promote weeds in the experimental crop rotation, while stubble retention suppresses weeds in untilled fields. The combined effects of stubble retention and no-tillage on weed suppression varied among the three crops. Based on these results, we recommend stubble retention in untilled legume-crop rotations on the Loess Plateau to improve the control of weeds.     

The role of models for multicriteria evaluation and multiobjective design of cropping systems for managing weeds

Weeds are both harmful for crop production and important for biodiversity, while herbicides can pollute the environment. We thus need new cropping systems optimising all cultural techniques, reconciling agricultural production, herbicide reduction and biodiversity conservation. Here, we show how to (i) develop models quantifying the effects of cropping systems on weed dynamics, (ii) integrate interactions between weeds and other organisms, (iii) predict the impact on production and biodiversity and (iv) use the model for multicriteria evaluation and multiobjective design of cropping systems. Among the existing weed dynamics models, we chose the one closest to our requirements to illustrate these different steps, that is, FlorSys which predicts multispecific weed dynamics as a function of cultural techniques and pedoclimate. We have illustrated the development of interaction submodels with the example of a crop pathogen whose propagation is increased when infecting grass weeds. To evaluate the weed flora impact, predicted weed densities were translated into indicators of harmfulness (crop yield loss, technical harvest problems, harvest pollution, field infestation, crop disease increase) and biodiversity (weed species richness and equitability, trophic resources for birds, insects and pollinators). Simulations were run over several years and with different weather scenarios (i) to optimise cultural techniques to control harmful weeds, (ii) to analyse the impact of changing agricultural practices (e.g. simplified tillage and rotations, no‐till, temporary crops) on weed density, species and trait composition and (iii) to evaluate cropping systems for their ability to reconcile agricultural production and biodiversity, thus identifying levers for designing sustainable cropping systems.     

Weed populations in winter wheat as affected by crop sequence, intensity of tillage and time of herbicide application in a cool and humid climate

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.