The necrosis issue involves is a problem not only for Slovakia but for Europe as well. The diploma thesis deals with the issue of ash necrosis in the LS Slanec model area. The work deals with the issue of health mass dying of ashes at LS Slanec. It also evaluated the overall health status of the trees from the aspect of external symptoms - defoliation and decolorization and monitoring of other possible causes of dying of ashes. An unfavorable state of health is currently the cause of the activation of the fungus Chalar fraxin and its vector Hylesinus fraxini. Based on the results obtained, protective and defensive measures were proposed to eliminate large-scale damage