One of the most important pathogen of our field and culture plant production is Sclerotinia sclerotiorum (white mold). In case of its epidemic spreading it causes significant production losses in sunflower fields. For this reason we consider it important to know more about the generative reproduction cycle and the interaction of ecological conditions to this pathogen. To establish the above we have conducted laboratory and field studies during various phenophases of the sunflower. For our experiment we used various genotypes (NK-254, Remil, NS-H-26, GK-70 and SP-1) and have found that the development of Sclerotinia sclerotiorum infection very much depends on the phenological state of the host and the microclimatic conditions. From the infection point of view the dampness of the surroundings and the light conditious (1500-1600 lux is the optimum) were decisive. The sporulation of the fungus is found at 60-95% relative humidity of the air and the spores germinate in 4-5 hours at 18-25°C. According to our observation for the mycelial imbedding in the host's tissues the leaves must be wet up to 30-35 hours. On the other hand, regular interruptions of wet period can result in the failure of infection. From the development of epidemic point of view the most critical period is the state of the beginning of the generative phases of budding, blooming and yellow ripening. Presently, depending on the meteorological factors, the spraying of sunflower plants is justified. The dampness of suroundings is vital in this regard.