The use of pesticides made it possible to increase yields, simplify cropping systems, and forego more complicated crop protection strategies. Over-reliance on chemical control, however, is associated with contamination of ecosystems and undesirable health effects. The future of crop production is now also threatened by emergence of pest resistance and declining availability of active substances. There is therefore a need to design cropping systems less dependent on synthetic pesticides. Consequently, the European Union requires the application of eight principles (P) of Integrated Pest Management that fit within sustainable farm management. Here, we propose to farmers, advisors, and researchers a dynamic and flexible approach that accounts for the diversity of farming situations and the complexities of agroecosystems and that can improve the resilience of cropping systems and our capacity to adapt crop protection to local realities. For each principle (P), we suggest that (P1) the design of inherently robust cropping systems using a combination of agronomic levers is key to prevention. (P2) Local availability of monitoring, warning, and forecasting systems is a reality to contend with. (P3) The decision-making process can integrate cropping system factors to develop longer-term strategies. Agron. Sustain. Dev. (2015) 35:1199-1215 DOI 10.1007 protection solutions. And (P8) integration of multi-season effects and trade-offs in evaluation criteria will help develop sustainable solutions.

Summary Despite the serious threat which weeds offer to organic crop production, relatively little attention has so far been paid to research on weed management in organic agriculture, an issue that is often approached from a reductionist perspective. This paper aims to outline why and how this problem should instead be tackled from a system perspective. Compared with conventional agriculture, in organic agriculture the effects of cultural practices (e.g. fertilization and direct weed control) on crop:weed interactions usually manifest themselves more slowly. It follows that weed management should be tackled in an extended time domain and needs deep integration with the other cultural practices, aiming to optimize the whole cropping system rather than weed control per se. In this respect, cover crop management is an important issue because of its implications for soil, nutrient, pest and weed management. It is stressed that direct (physical) weed control can only be successful where preventive and cultural weed management is applied to reduce weed emergence (e.g. through appropriate choice of crop sequence, tillage, smother/cover crops) and improve crop competitive ability (e.g. through appropriate choice of crop genotype, sowing/planting pattern and fertilization strategy). Two examples of system‐oriented weed management systems designed for organic agriculture are illustrated as well as future perspectives and problems.

Increasing concerns about pesticide use and a steadily increasing conversion to organic farming have been major factors driving research in physical and cultural weed control methods in Europe. This article reviews some of the major results achieved with nonchemical methods and strategies, especially adapted for row crops (e.g., corn, sugar beet, onion, leek, and carrot) and small-grain cereals (e.g., barley and wheat). In row crops, intrarow weeds constitute a major challenge, and research has mainly aimed at replacing laborious hand-weeding with mechanization. A number of investigations have focused on optimizing the use of thermal and mechanical weeding methods against intrarow weeds, such as flaming, harrowing, brush weeding, hoeing, torsion weeding, and finger weeding. And new methods are now under investigation such as robotic weeding for row crops with abundant spacing between individual plants and band-steaming for row crops developing dense crop stands. The strategic use of mechanical weed control methods in small-grain cereals has been another area of considerable interest. Weed harrowing and interrow hoeing provide promising results when they are part of a strategy that also involves cultural methods such as fertilizer placement, seed vigor, seed rate, and competitive varieties. Although research in preventive, cultural, and physical methods have improved weed control in row crops and small-grain cereals, effective long-term weed management in low external input and organic systems can only be achieved by tackling the problem in a wider context, i.e., at the cropping system level. Basic principles of this approach, examples of cover crop and intercropping use for weed suppression, and an application in a 2-yr rotation are presented and discussed.

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Size and composition of the weed seedbank was assessed after 12 years of application of four tillage systems in two crop rotations. Mouldboard and chisel ploughing at 45 cm, minimum tillage at 15 cm and no tillage were compared in continuous winter wheat and a pigeon bean/winter wheat 2‐year rotation. Weed control was based upon post‐emergence herbicide application. Weed seedling emergence from soil samples taken at 0–15, 15–30 and 30–45 cm depths was assessed in a non‐heated glasshouse for 12 months. The tillage system influenced weed seedbank size and composition to a much greater extent than crop rotation. Total weed seedling density was higher in no tillage, minimum tillage and chisel ploughing plots in the 0–15, 15–30 and 30–45 cm layers respectively. Density in the whole (0–45 cm) layer did not differ significantly among tillage systems. With no tillage, more than 60% of the total seedlings emerged from the surface layer, compared with an average 43% in the other tillage systems. Crop rotation did not influence either weed seedbank size or seedling distribution among soil layers, and only had a small influence on major species abundance. The weed seedbank was dominated (>66%) by Conyza canadensis (L.) Cronq. and Amaranthus retroflexus (L.), which thrived in chisel ploughing and no tillage respectively. Results suggested that crop rotation and substitution of mouldboard ploughing by non‐inversion tillage (especially by minimum tillage) would not result in increased weed problems, whereas use of no tillage might increase weed infestations because of higher seedling recruitment from the topsoil.

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Summary The objective of this study was to obtain detailed information on the long‐term weed suppression potential of four winter soil cover types included in an arable crop system managed at various input levels. We used weed seedbank size and composition to assess weed suppression potential. A field experiment was established in 1993 as a split‐split‐plot design with four replications, including two tillage systems [a conventional system (CS) including ploughing in the cover crops and a low‐input system (LIS) including no tillage with surface mulching of the cover crops] in the main plots, three mineral nitrogen fertilization rates for the main crop in the sub‐plots and four soil cover types (main crop residue, rye, crimson clover and subterranean clover) in the sub‐sub‐plots. Seedbank sampling took place in winter 2000/01. The weed seedbank was analysed with the seedling emergence method. Data were analysed using anova and multivariate techniques. Results indicated that the seedbank density in the LIS was about five times higher than in the conventional input system. In the CS, use of a rye cover crop resulted in a lower seedbank density with respect to the crop residue treatment (−25%), whereas in the LIS the subterranean clover cover crop decreased weed seedbank density as compared with the other cover crops and the crop residue treatment (−22% on average). Differences in species composition were mainly related to tillage system. Implications for cover crop management and the development of sustainable cropping systems are discussed.

Reduced tillage is increasingly promoted to improve sustainability and productivity of agricultural systems. Nonetheless, adoption of reduced tillage by organic farmers has been slow due to concerns about nutrient supply, soil structure, and weeds that may limit yields. Here, we compiled the results from both published and unpublished research comparing deep or shallow inversion tillage, with various categories of reduced tillage under organic management. Shallow refers to less than 25 cm. We found that (1) division