Since the causative agent of barley mottle disease, the fungus Ramularia collo-cygni, only appeared in Europe in the mid-1980s, it remained a scientifically unknown entity for a long time. For the first time, extensive research into the biology of this fungus was carried out in Austria. In time-step experiments it was shown that there is a strong dependence of the expression of symptoms on the physiological developmental state of the barley. In order to be able to record the genotypic resistance differences of the winter barley varieties, the rating data were cleaned of the influence of the timing of ear emergence using a regression residual method.