This diploma thesis is interested in effective defense against necrosis of ashes. This disease influ-ences the ash population throughout whole Europe at present. Part of the diploma thesis is inte-rested in function of the ash patosystem. Within this research was realised complex analysis of the soil focused on physically-chemical and chemical atributes of the soil. On the partial variants were aplicated preparations with fungicidal behavior which were applied on the surface of the assimilation part of the plant. Substances should worked negative against successful germination of the ascospores on the leaves of the affected trees. In the second direction of the research was used nitrogen fertilizers which should positively influenced vitality of the host trees and together accelerated decomposition infected saps on the soil surface. Efficiency of defensive measures was evaluated with help of the periodical evaluation of health condition of the treated trees on the research areas. To this rating was used methodology Health condition the forest of ashes evaluation (Rozsypálek, 2015). Efficiency of the substance takes effect by braking or complete stopping worsening health condition. For stopping worsening health condition was recommended applying 20-25 l. ha concentrate Vermaktiv Stimul S16 with ionic sulfur in a higher proportion. Ratio of dilution with water is 1:50 – Vermaktiv S16 – water. As another active substance in relation with health vitality was evaluated ammonium sulfate. This application is implemented on the soil surface with recommended ration 750 kg. ha which represents 150 kg pure nitrogen per 1 ha.