In this paper the short description of leaf mining month (Cameraria ohridella) and their development stages are presented as well as their bionomical expansion and gradation. Cameraria ohridella has been the serious pest of horse chestnut in Slovak Republic since 1994. Together with phytophatogenic fungi (particularly Guignardia aesculi) appears to be one of the primary guestion of premature mass drying up and leafless of horse chestnut. The paper is describing effective system of the chemical control, which was verified in 1998. This system is based on a combination of insecticide pyretroides and organo-phosphate groups together with natural terpene. New proposed and developed sprayer with range of vertical spraying 25 m removed the existing practical problem of chemical control, which is height of the trees. This system indirectly protects the trees against infection by pathogenic fungi.