SummaryWeed control research to date has mainly focused on arable land, especially regarding herbicides, but also regarding non-chemical methods. Some of these experiences can be applied to hard surface areas. However, weeds on hard surface areas cause problems that are different from those on arable land. Additionally, crop tolerance does not need to be considered when choosing an appropriate weed control method on these areas. The aim of this review is to describe current knowledge of weeds and weed control methods on hard surface areas and reveal potential ways of advancement. One of the shortcomings of non-chemical weed control on hard surfaces thus far, is a lack of proper definition of efficiency of the weed control methods. To obtain effective control, more frequently repeated treatments are required than chemical weed management, thereby increasing the costs of labour and fuel. One way to reduce costs can be by adjusting the level of control to the required visual street quality. Weeds are adapted to the hard surface environment and may be less susceptible to certain control methods. This review indicates that for efficient weed control on hard surfaces there is a need for combining weed control techniques, applying sensors for detecting weeds, adapting the energy dose to type of weed flora and prevention of weeds by improved construction of new surfaces.

Management of turfgrass on football pitches without pesticides involves a considerable challenge for weed control. By improving conditions for grass growth by cultural practices, weeds may be repressed by stronger competition from the grass. A 3-year field trial on 37 football pitches investigated the effects of various cultural management practices on percentage grass, weed and bare ground, respectively. The trial included twelve different treatments, comprising different combinations of fertiliser level and cultural methods, including two types of spring-tine harrow, vertical cutting, over-seeding, and top-dressing. Some treatments resulted in significant differences in percentage grass and weed cover, but not in percentage bare ground. However, other factors, such as locality of the football pitch, zone on the pitch, month, year, playing frequency, cutting frequency and, particularly, ground cover at the beginning of the trial, also contributed considerably to the variation in ground cover, indicating that established weeds are difficult to eradicate.

Summary An analysis of the regulations of herbicide use for weed control in non‐agricultural/urban amenity areas, including actual pesticide use, was carried out as a joint survey of seven European countries: Denmark, Finland, Germany, Latvia, the Netherlands, Sweden and United Kingdom. Herbicides constitute the major part of the pesticides used in urban amenity areas. Herbicide use on hard surfaces is the largest in terms of volume and potential contamination of surface and groundwater. The aim of the study was to investigate the differences in political interest and public debate on the ‘use of pesticides in public urban amenity areas’, regulations within each country at national, regional and local levels, possible use of alternative weed control methods and the amounts of pesticides used on urban amenity areas. A comparative analysis revealed major differences in political interest, regulations and availability of statistics on pesticide use. Denmark, Sweden, the Netherlands and Germany have, or have had, a strong public and political interest for reducing the use of herbicides to control weeds in urban amenity areas and also have very strict regulations. The UK is currently undergoing a period of increasing awareness and strengthening regulation, while Latvia and Finland do not have specific regulations for weed control in urban amenity areas or on hard surfaces. Statistics on pesticide/herbicide use on urban amenity areas were only available in Denmark and the Netherlands. Developing this kind of information base reveals the differences in herbicide use, regulations and policies in European countries and may enhance the transfer of knowledge on sustainable weed control across countries.

To be proactive in minimizing pesticide use, the public authorities in Denmark agreed in 1998 to phase out the use of pesticides on publicly owned areas by the end of 2002. A part of the agreement was an increasing focus on research into and development of new methods and implements for non-chemical weed control on paved areas. Due to a large increase in the costs of non-chemical weed control, the park authorities have to put the different types and locations of paved areas in order of priority to optimize the weed control effort. The present authors divided the paved areas into five weed control levels, dependent on placement, quality and use. For the 3 years 1999-2001, experiments with different non-chemical weed control methods were conducted on pavements at six locations in Denmark. The aim was to test the reaction of the weeds to different treatments and strategies. The efficacies of the methods were evaluated by analysis of digital images to estimate the fraction of the paved area covered with green vegetation (weed coverage). The weed coverage was used as the dependent variable in the subsequent statistical analysis. The independent variables in the model were incoming radiation, wear, area of joints in the pavement, the dying process of the weeds and the number of runs/applied energy of the mechanical or thermal weed control methods, respectively. The estimated parameters from the statistical model were used to build a simulation model, which was used to optimise five weed control strategies to fulfil the suggested weed control levels. In the suggested strategy for maximum weed control, 12 thermal weeding applications at 2-week intervals are suggested. The 'clean-up' strategy is based on one weed-brushing in late spring or early autumn.

Summary The efficacy of five non‐chemical weed control methods for reducing weed cover on traffic islands was investigated in the growing season of 2004. Three trial sites were divided into six treatment areas which were treated with either flame, steam, hot air, hot water, brushes or left untreated. The treatments were carried out at regular intervals throughout the growing season. The percentage weed cover was measured every second week using a 75 × 75 cm quadratic frame with 100 squares. In the control areas, a rapid increase in weed cover was observed, whereas all treatments reduced weed cover. Hot water was the most effective method, although not significantly better than hot air or steam. Hot air treatment was more effective than brushing, whereas hot water was more effective than both flaming and brushing. The doses that were used were relatively high (150–355 kg ha−1), partly because of the irregular shape of the traffic islands and the treatment intervals were quite short in comparison with those in similar studies. However, the treatments could keep down the weeds only to a certain extent. The present knowledge of the efficacy of various weed control methods, as well as an increase in our knowledge of adequate treatment intervals, supports an optimisation of hard‐surface weed control. Data and experience gained from these trials were used to develop further calibrated application studies.

Kentucky bluegrass (Poa pratensis L.) is often poorly established when sown in turfgrass seed mixtures with slender creeping red fescue (Festuca rubra L. ssp. litoralis Vasey) and perennial ryegrass (Lolium perenne L.), possibly because of its slow emergence and slow seedling growth. This study investigated the effect of sowing Kentucky bluegrass earlier than red fescue and perennial ryegrass on the botanical composition of the established turfgrass. In field experiments established during 2 yr, red fescue and perennial ryegrass were sown at weekly intervals from zero to 35 d [0–679 degree‐days (°days) with a base temperature of 0°C] after Kentucky bluegrass had been sown in the same plot. Nine or twelve months after establishment, the botanical composition was estimated. When the species were sown simultaneously, Kentucky bluegrass only constituted 3 to 30% of the tillers, although the species constituted 50 to 59% of the viable seeds of the seed mixture. Delayed sowing of red fescue and perennial ryegrass significantly improved the establishment of Kentucky bluegrass, i.e., the percentage of tillers could be increased by up to 0.08% for every °day Kentucky bluegrass was sown before red fescue and perennial ryegrass. There was a corresponding negative effect on the percentage tillers of red fescue and primarily perennial ryegrass. In certain cases, the relationship between percentage tillers and difference in sowing time was better described by a nonlinear function, indicating an increasing effect when difference in sowing time was large.

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An experiment was conducted on a specially designed hard surface to study the impact of time interval between flaming treatments on the regrowth and flower production of two grass weeds. The goal of this experiment was to optimize the control of annual bluegrass and perennial ryegrass, both species that are very difficult to control without herbicides. Aboveground biomass from 72 plants per treatment was harvested and dry weights were recorded at regular intervals to investigate how the plants responded to flaming. Regrowth of the grasses was measured by harvesting aboveground biomass 2 wk after the second flaming treatments that were implemented at different time intervals. Flaming treatments decreased plant biomass of both species and also the ratio of flowering annual bluegrass plants. However, few plants were killed. The first flaming treatment affected aboveground biomass more than the second flaming treatment. A treatment interval of 7 d provided the greatest reduction in regrowth of perennial ryegrass, whereas the effect of treatment interval varied between the first and second repetitions of this experiment for annual bluegrass. In general, short treatment intervals (3 d) should be avoided, as they did not increase the reduction of aboveground biomass compared with the 7-d treatment interval. Knowledge on the regrowth of grass weeds after flaming treatments provided by this study can help improve recommendations given to road keepers and park managers for management on these weeds.