Suchergebnisse

Cirsium arvense (L.) Scop. is a troublesome weed, causing economic losses by reducing crop yield, increasing herbicide and tillage costs, and degrading soils due to increased tillage requirements. The major control method for C. arvense is herbicide application, but this poses socio-environmental and herbicide resistance risks. The European Union promotes reduced dependence and sustainable use of herbicides, combined with cultural and mechanical weed control. This thesis assessed the effects of integrated weed control on the population dynamics of C. arvense. For mechanical control, farmers are recommended to act when C. arvense is most sensitive to disturbance, i.e. at the point of minimum belowground weight, coinciding with 7-10 leaves per shoot. However, many farmers believe that this is too late. To estimate the compensation point (CP), defined as the minimum weight of the entire belowground structure of C. arvense, and identify links between initial root weight, planting depth and crop competition, three outdoor pot experiments were performed. For chemical control, farmers are recommended to spray when the majority of C. arvense shoots are 10-20 cm high. To assess the effects of timing and dose of herbicide application (MCPA), and crop competition on growth and development of C. arvense, one outdoor pot experiment and one field experiment were performed. The field experiment also assessed the effects of selective cutting. It was found that CP for C. arvense occurred before 3-leaf stage and that treatment effects were minor (<0.5 leaf stages). Depletion of planted root fragments ceased on average around leaf stage 3-4, indicating that CP occurs at early leaf stages. In the pot experiment, the strongest effect of herbicide treatment was obtained by spraying with the recommended dose in the presence of a crop when the largest C. arvense shoot had 3-4 leaves, corresponding to maximum height 13 cm and median height 6 cm. Crop competition reduced biomass, shoot height and leaf production of C. arvense regardless of herbicide dose. In the field experiment, herbicide treatment at 4-5 leaves or 8-10 leaves gave similar control effects as selective cutting. Herbicide application had a more immediate effect on growth and development of C. arvense while selective cutting depleted the below-ground structures more gradually. The results indicate that mechanical control of C. arvense should be performed earlier than previously recommended, probably before C. arvense reaches 3-4 leaves per shoot. Also early herbicide spraying seems to be as efficient as spraying later in the season.