The impact of the pathogenic rust fungus Puccinia punctiformis on the population dynamics of the clonal host plant Cirsium arvense was studied using field data and a matrix population model. To account for the spatial growth pattern of C. arvense, the study area was divided into cells of 10 × 10 cm. The cells were classified as empty (no C. arvense shoots), diseased (shoots infected by P. punctiformis), or healthy. The spatial growth pattern of C. arvense could be described as static or dynamic. Abundance of C. arvense depended largely on dynamic clonal growth. Shoots produced by dynamic clonal growth had a lower probability to be infected by P. punctiformis than shoots produced by static clonal growth. Dynamic clonal growth seemed to serve as a mechanism of disease escape. The results are discussed with respect to the use of P. punctiformis as biological agent for control of C. arvense in grasslands. Key words: clonal growth, disease escape, Puccinia punctiformis, Cirsium arvense, biological weed control.