The dynamics of competitive colonisation of necrotic cyclamen tissue by the plant pathogenic fungus Botrytis cinerea and the saprophytic fungal antagonist Ulocladium atrum were studied immuno-histologically, while sporulation was studied macroscopically. The effect of different time intervals between inoculation of both fungi on resource capture by each species was explored. Colonisation and sporulation were used as indicators for competitive resource capture and the effectiveness of biological control of B. cinerea, using U. atrum. Mycelial biomass and sporulation showed logistical time courses in both species, in monocultures as well as in mixed cultures. Final colonisation and sporulation levels were lowered by competition, indicating competitive resource capture. Analysis of the extent to which sporulation of either fungus could be reduced by co-inoculation with the other fungus at different times, showed that B. cinerea can be completely excluded by ‘early’ pre-inoculation with U. atrum, but not vice versa, indicating that U. atrum can exploit resources in the leaf that are not accessible to B. cinerea. A model of competitive substrate colonisation and resource capture was developed on the basis of the experimental results. Model results confirm that competition for resources provides a sufficient biological explanation for the dynamic interactions between the fungi. The model provides a tool to optimise dose and timing of U. atrum applications providing effective biological control of B. cinerea.