In numerous localities of Slovakia, the deteriorating health status of European ash (Fraxinus excelsior) can be detected, while the major role in languish and dieback process is played by fungus Chalara fraxinea, alongside with an activated wood-boring insect Hylesinus fraxini overpopulated on the debilitated tree. The aim of the bachelor's thesiswas to detect damage rate of pathogen, but mainly describe secondary harmful factor Hylesinus Fraxini effecting European ash dieback in Slovakia and to map the scope and dynamics of European ash deterioration in the woods, within the assessed territory of Strážovské vrchy. On the basic of data analysed,the presence of the primary harmful agent cannot be confirmed, but presence of secondary, clearly confirms it.The health of the ash in evaluated area is not encouraging. Over the past two years, trappings have been transported overcrowded with pestsThe thesis proposes precautionary measures alleviating the consequences and depicts protection measures increasing the vitality of the plants.