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Enhanced understanding of soil disturbance effects on weed seedling recruitment will help guide improved management approaches. Field experiments were conducted at 16 site-years at 10 research farms across Europe and North America to (i) quantify superficial soil disturbance ( SSD) effects on Chenopodium album emergence and (ii) clarify adaptive emergence behaviour in frequently disturbed environments. Each site-year contained factorial combinations of two seed populations (local and common, with the common population studied at all site-years) and six SSD timings [0, 50, 100, 150, 200 day-degrees (d°C, base temperature 3°C) after first emergence from undisturbed soil]. Analytical units in this study were emergence flushes. Flush magnitudes (maximum weekly emergence per count flush) and flush frequencies (flushes year−1) were compared between disturbed and undisturbed seedbanks. One year after burial, SSD promoted seedling emergence relative to undisturbed seedbanks by increasing flush magnitude rather than increasing flush frequency. Two years after burial, SSD promoted emergence through increased flush magnitude and flush frequency. The promotional effects of SSD on emergence were strongest within 500 d°C following SSD; however, low levels of SSD-induced emergence were detected as late as 3000 d°C following SSD. Accordingly, stale seedbed practices that eliminate weed seedlings should occur within 500 d°C of disturbance, because few seedlings emerge after this time. However, implementation of stale seedbed practices will probably cause slight increases in weed population densities throughout the year. Compared with the common population, local populations exhibited reduced variance in total emergence measured within sites and across SSD treatments, suggesting that C. album adaptation to local pedo-climatic conditions involves increased consistency in SSD-induced emergence. [ABSTRACT FROM AUTHOR]

S alonen J, H yvönen T, K aseva J & J alli H (2012). Impact of changed cropping practices on weed occurrence in spring cereals in Finland - a comparison of surveys in 1997-1999 and 2007-2009. Weed Research. Summary During recent decades, arable cropping has been intensified to increase production, but has also been constrained by agri-environment schemes. Weed populations respond to such changes, thus indicating trends in cropping practices. In Finland, repeated monitoring of the weed flora aims to record and understand the response of weed populations to changing cultural conditions. Two recent surveys of the weed flora in Finnish spring cereal fields, conducted in 1997-1999 and 2007-2009, were evaluated to assess the effect of known changes in tillage practices and herbicide use on weed occurrence. The same 382 fields were assessed during both decades. In conventional cropping, the total abundance of weeds has remained at about the same level as recorded in the late 1990s. Overwintering weed species like Galium spurium, Lamium spp., Lapsana communis and Poa annua have become more frequent, indicating a trend towards reduced primary tillage. Increased use of glyphosate has in turn led to a decline in Elymus repens, particularly in non-ploughed fields. Substantially increased total biomass of weeds was associated with organic cropping, due to lack of direct weed control methods and inadequate crop competition. The opposite trend was apparent in the fields, which had returned from organic farming back to conventional cropping. The results suggest that more decisive IPM strategies are required, both in organic cropping to stop the increasing weed biomass and in conventional cropping to reduce current reliance on herbicides. [ABSTRACT FROM AUTHOR]

Brandsæter LO, Fogelfors H, Fykse H, Graglia E, Jensen RK, Melander B, Salonen J & Vanhala P (2010). Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens. Weed Research 50, 102–109. The success of weed management aimed at depleting the regenerative structures of perennial weeds depends largely on the sprouting activity of rhizome and root buds. Seasonal variation in sprouting of these buds on Cirsium arvense, Sonchus arvensis and Elymus repens was studied for plants collected from Denmark, Finland, Norway and Sweden. At 2-week intervals from July to October, 5-cm fragments of roots or rhizomes were cut from plants grown in buckets and planted into soil in pots, half of which were placed immediately into growth chambers at 18°C for 4 weeks. The other half of the pots were initially placed in a dark room at 2°C for 4 weeks before being transferred to the same growth chamber, also for 4 weeks. During the growth chamber period, the numbers of emerged shoots in each pot were counted weekly. The sprouting activity of C. arvense and E. repens was relatively uniform during this period and bud dormancy was not apparent. In all ecotypes of S. arvensis, innate bud dormancy developed during the latter part of the growing season. For all three species, differences in sprouting readiness were found among ecotypes. The results imply that C. arvense and E. repens are more likely to be controlled by mechanical measures in autumn than S. arvensis. [ABSTRACT FROM AUTHOR]

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