In 1998–2001 the studies on one-year-old and two-year-old plantations of St. John’s wort (Hypericum perforatum L.), cultivar Topaz were carried out. The percentages of plants with diseases symptoms as well as indexes of infected plants were examined directly in the field. The fungi were isolated from superficially disinfected plants fragments namely from roots, stem bases and leaves, using in first year mineral culture medium and the next years St. John’s wort glucose extract agar. Necrosis of the roots of one-year-old and two-year-old plants were observed. Morover the disintegration and softening of lower parts of shots occurred. Plant organs with such disease symptoms were colonized by a complex of pathogenic fungi wherefrom Fusarium spp., Rhizoctonia solani, Botrytis cinerea and Phoma exigua var. exigua turned out to be of economic importance. Among the species of Fusarium colonizing the roots of one-year-old and two-year-old plants F. avenaceum, F. culmorum, F. equiseti, F. oxysporum and F. solani most often occurred. This species of Fusarium were isolated from external as well as from internal part of shoots of two-year-old plants. Seimatosporium hypericinum, not yet recorded in Poland, was commonly obtained from the stems showing cracks in the bark of diseased stems as well as from leaves showing red-amber necrotic spots.

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