Picture above shows a willow mixture trial comprising monoculture plots and different designs of 3- or 5-clone mixture plots (3 replicates). The brown patches are defoliated  monoculture plots of 2 susceptible clones.

Large scale monoculture plantings are vulnerable to pathogen attacks. A strategy to reduce such a risk is to plant clonal mixtures to increase genetic diversity. Because genotype mixtures are readily accepted for biomass production and conservation, willows have a unique advantage over food or horticultural crops, in which flavour, colour, and shape may have prime importance. The experience in Europe over the last 15 years suggests that, compared with monoclonal plantings, mixtures can, in general, reduce disease levels. However, performances of different mixtures vary. Disease level is significantly reduced in some mixtures while remains similar or even increased in others. An understanding of how different mixtures affect pathogen population is crucial in deciding what combinations of willows are best suited for mixtures.