Epsilon Open Archive

Abstract

Sonchus arvensis L. is a perennial weed that is widely prevalent in annual crops in northern Europe and can cause substantial yield losses. The abundance of S. arvensis has increased recently, primarily due to expansion of organic farming and increased use of reduced tillage. This thesis assessed the effect of mechanical control measures on the population dynamics of S. arvensis and sought to predict the impact of temperature on sprouting of S. arvensis under variable climate conditions. An outdoor box experiment was performed to evaluate the effect of initial root fragment size on subsequent growth of S. arvensis. Four artificial populations of S. arvensis with differing initial root length but with the same total root length per area were planted (20 roots of 5 cm, 10 roots of 10 cm, 20 roots of 5 cm and 4 × 20 cm + 4 × 5 cm roots). A pot experiment was performed in darkness to assess the impact of initial root length (5 and 10 cm), temperature (4, 8 and 18 °C) and planting depth (3, 10 and 17 cm) on belowground shoot elongation and emergence time of S. arvensis shoots. The data from this pot experiment were used to model shoot emergence rate as a function of temperature and to predict emergence time under different climate scenarios.

Degree of root fragmentation was found to strongly infl uence plant performance in terms of shoot emergence time, shoot numbers, rosette size, flowering, biomass production and seed production. Compared with larger root fragments, small root fragments of S. arvensis produced more numerous but smaller-sized shoots, which emerged later in the beginning of the growing season and had lower generative capacity in terms of seed and root production. Root fragmentation by mechanical control measures resulted in a change not only in the frequency of shoots originating from S. arvensis root fragments, but also in the height of these shoots. Temperature significantly affected sprouting and emergence time of S. arvensis, with an increase in temperature causing an increase in the rate of S. arvensis shoot elongation. Variations in temperature between years under field conditions (in central Sweden) resulted in larger variations in emergence time than differences in root fragment weight. An average increase in mean air temperature of about 3 °C would cause earlier emergence, approximately equal to the difference between the earliest and latest year in the present climate.