2014). Influence of cutting time and stubble height on regrowth capacity of Juncus effusus and Juncus conglomeratus. Weed Research 54, 603-613.Fig. 1 Regrowth of shoots during the season 2009 from two ecotypes (western and eastern Norway) of Juncus effusus and J. conglomeratus, measured as dry weight of shoots per unit, in a growth chamber at 17.5°C. Each point represents shoot dry weight for one unit. The lines show quadratic functions for the given ecotype, species and stubble heights, based on the fitted model. © 2014 European Weed Research Society 54, 603-613 J. conglomeratus -West Norway (2010) J. effusus -West Norway (2010) J. effusus -East Norway (2010) J. conglomeratus -East Norway (2010) Fig. 2 Regrowth of shoots during the season 2010 from two ecotypes (western and eastern Norway) of Juncus effusus and J. conglomeratus at 17.5°C. Each point represents shoot dry weight for one unit. The lines show quadratic functions for the given ecotype, species and stubble heights, based on the fitted model.

Increasing abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) in pastures and meadows in western Norway has caused reductions in forage yield and quality in recent decades. Understanding plant development and regrowth following cutting is essential in devising cost-effective means to control rushes. In a field experiment in western Norway, we investigated development of above-and below-ground fractions of rush from seedlings to three-year-old plants, including the impact on vigour of disturbing growth by different cutting frequencies during the period 2009-2012. Each year, the plants were exposed to one or two annual cuts or left untreated and five destructive samplings were performed from March to early December. Juncus effusus showed significantly more vigorous growth than Juncus conglomeratus in the last two years of the study period. The aboveground:below-ground biomass ratio of both species increased mainly in spring and early summer and was reduced in late summer and autumn. Removal of aerial shoots also reduced the below-ground fraction of both species. One annual cut in July effectively reduced biomass production in both species by 30-82%, which was only a slightly smaller reduction than with two annual cuts, in June and August. Mechanical control measures such as cutting can thus effectively reduce rush vigour when performed late in the growing season.

Reusing soil can reduce environmental impacts associated with obtaining natural fresh soil during road construction and analogous activities. However, the movement and reuse of soils can spread numerous plant diseases and pests, including propagules of weeds and invasive alien plant species. To avoid spread of barnyardgrass in reused soil, its seeds must be killed before that soil is spread to new areas. We investigated the possibility of thermal control of barnyardgrass seeds using a prototype of a stationary soil steaming device. Four Norwegian and one Polish seed population were examined for thermal sensitivity. To mimic a natural range in seed moisture content, dried seeds were moistened for 0, 12, 24 or 48 h before steaming. To find effective soil temperatures and whether exposure duration is important, we tested target soil temperatures in the range 60 to 99 C at an exposure duration of 90 s (experiment 1) and exposure durations of 30, 90 or 180 s with a target temperature of 99 C (experiment 2). In a third experiment we tested exposure durations of 90, 180 and 540 s at 99 C (experiment 3). Obtaining target temperatures was challenging. For target temperatures of 60, 70, 80 and 99 C, the actual temperatures obtained were 59 to 69, 74 to 76, 77 to 83 and 94 to 99 C, respectively. After steaming treatments, seed germination was followed for 28 days in a greenhouse. Maximum soil temperature affected seed germination, but exposure duration did not. Seed pre-moistening was of influence but varied among temperatures and populations. The relationships between maximum soil temperature and seed germination were described by a common dose-response function. Seed germination was reduced by 50% when the maximum soil temperature reached 62 to 68 C and 90% at 76 to 86 C. For total weed control, 94 C was required in four populations, whereas 79 C was sufficient in one Norwegian population.

Summary The abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) has increased in coastal grasslands in Norway over recent decades, and their spread has coincided with increased precipitation in the region. Especially in water‐saturated, peaty soils, it appears from field observations that productive grasses cannot compete effectively with such rapidly growing rush plants. In autumn–winters of 2012–2013 and 2013–2014, a four‐factor, randomised block greenhouse experiment was performed to investigate the effect of different soil moisture regimes and organic matter contents on competition between these rush species and smooth meadow‐grass (Poa pratensis). The rush species were grown in monoculture and in competition with the meadow‐grass, using the equivalent of full and half the recommended seed rate for the latter. After about three months, above‐ and below‐ground dry matter was measured. J. effusus had more vigorous growth, producing on average 23–40% greater biomass in both fractions than J. conglomeratus. The competitive ability of both rush species declined with decreasing soil moisture; at the lowest levels of soil moisture, growth reductions were up to 93% in J. conglomeratus and 74% in J. effusus. Increasing water level in peat–sand mixture decreased competivitiveness of meadow‐grass, while pure peat, when moist, completely impeded its below‐ground development. These results show that control of rush plants through management may only be achieved if basic soil limitations have been resolved.