The effect of stubble tillage and primary tillage on population dynamics of Canada Thistle (Cirsium arvense) in organic farming

Summary

Canada Thistle (Cirsium arvense) is a widespread weed in organic farming. It is difficult to control and in many farming enterprises there is a tendency of increase. Reduced frequency and intensity of tillage may be one reason for increasing problems. We studied the impact of stubble tillage and primary tillage on population-dynamics of C. arvense. In this paper results are presented of two field experiments at the ‘Experimental Station for Organic Farming Kleinhohenheim’, one field experiment on ‘Goldener Acker’ at Hohenheim and 19 experiments on organic farms south of Stuttgart. The experiments were carried out between 1998 and 2003.
Results show that inversion in autumn or winter is vital for the control of C. arvense. In an experiment testing various ploughing options plus non inversion tillage C. arvense rapidly increased in plots with yearly non inversion tillage but was kept at a low level in ploughed plots, with lower densities of C. arvense shoots in plots with deep ploughing compared to shallow ploughing.
Experiments on stubble tillage showed that tillage in summer effectively can reduce growth of C. arvense. However, shallow ploughing which was seen as the optimal option before the widespread introduction of herbicides appears to have no advantages compared to stubble tillage operations by a cultivator, rototiller or other machines. So, modern machinery adequately controls C. arvense and there is no need for a renaissance of the old fashioned shallow plough.
We conclude that tillage during summer and autumn is vital to control C. arvense and therefore to achieve adequate yields. Another important component for keeping C. arvense and other perennial weeds on a reasonable level is an adequate proportion of perennial fodder crops within the rotation.