AbstractInfluence of age on the susceptibility of poplar leaves to Marssonina brunnea.Investigations showed aclose relationship between the age of poplar leaves and their susceptibility toM. brunnea. The susceptibility is low during Hushing, it increases rapidly in the unfolding leaves, decreases in the mature ones, and finally rises again in the senescent leaves. This was the case both lor different clones and also for different methods of raising them.