The purpose of the investigations was to determine the efficacy of different conidia concentrations of Phomopsis convolvulus Ormeno on different leaf stages of Convolvulus arvensis seedlings and regrowth potential of C. arvensis 25 days after inoculation. Furthermore, the potential of P. convolvulus on the growth of C. arvensis derived from different root lengths was studied. The results showed a great reduction in dry weight of above-ground biomass with more than 80% irrespective of the conidia concentration (1 x 10(6), 10(7) and 10(8) conidia/ml) on plants of the leaf stage 1-3 and 5-7 and gave more than 80% reduction of root biomass with an exception in case of 1 x 10(6) conidia/ml on plants of the leaf stage 9-11. Mortality was reached complete only with 1 x 10(8) conidia/ml on plants of the leaf stage 1-3. Regrowth potential of C. arvensis at more developed leaf stages was higher than at early leaf stages. Within the 3 categories of root lengths tested (5, 10 and 15 cm), the 1-3 leaf stage shoots showed the highest susceptibility to P. convolvulus. Obtained results illustrate that the application of P. convolvulus with 1 x 10(8) conidia/ml at the young leaf stage (1-3 leaf stage) on all treatments give a great reduction of biomass and adversely affects regeneration of the plants.