Common horse-chestnut (Aesculus hippocastanum) is an introduced plant and has been successfully used for planting for a long time in Lithuania. The state of the A. hippocastanum growing in larger cities was assessed in 1992-2009. Moreover, the assessment was carried out throughout the entire country during 2006-09. The results of the research described the changing situation of A. hippocastanum during the investigative period: the state was sufficiently good for separate periods, but it began to deteriorate in 1995-97, when a A. hippocastanum was infected with fungi diseases (agents – Guignardia aesculi, Erysiphe flexuosa, and Schizophyllum commune). Unfavourable environmental conditions had also made an influence, whereas horse-chestnut leafminer (Cameraria ohridella) was the most harmful pest over all territory of Lithuania since 2005-06. This invasive pest is common in most European countries. Noteworthy of fallen leaves elimination is the most effective mean restraining abundance of C. ohridella and the spread of fungi diseases.
From the rhizosphere of investigated pot plants six Verticillium species (V. alboatrum, V. dahliae, V. nigrescens, V. nubilum, V. album and V. fusisporum), potentially dangerous to plants, were isolated. Most often colonized rhizospheres of diseased pot plants by Verticillium album were those of Peperomia obtusifolia and Calathea picturata (relative density 8%). Relative density of Verticillim group in other sick plants rhizosphere was up to 4% whereas that of the healthy looking plants varied from 1 to 3%. Pot plants are very sensitive to factors unfavourable to their growth.