Strategies to control Cirsium arvense under organic farming conditions

Summary

Three strategies for controlling Cirsium arvense including (1) repeated stubble tillage with subsequent forage crop cultivation, (2) repeated mowing of a grass-clover ley, and (3) forage crop cultivation following a grass-clover ley ploughed in May/June (3) were investigated in field experiments over 3 years. The development of C. arvense shoot density was regularly assessed on sub-plots with defined thistle densities. In the medium-term (9 months), treatment 1 decreased shoot density and regrowth capacity of C. arvense more effectively than a mowed grass-clover ley (2). However, after 22 months, treatments 1 and 2 resulted in a similar strong reduction of C. arvense shoot density of 95 % and 97 %, respectively. At this time, the efficacy of treatment 3 was lower (89 %), however, not significantly different to that of treatments 1 and 2. After 26 months, the effect of all treatments was still apparent; however, the efficacy of treatment 3 was significantly lower than that of treatment 2. Generally, the different strategies showed only minor differences, thus delivering options for optimal strategies of thistle control under given specific conditions of site and cropping systems.