Three active substances of corn. fungicides used for rapeseed protection (thiophanate-methyl, tebuconazole, prochloraz) were modified by addn. of corn. adjuvants (trisiloxane with polyether substituents, ethoxylated isodecyl alc., rapeseed oil Me ester) and studied in vitro for growth limitation of pathogen mycelia (Botrytis cinerea, Sclerotinia sclerotiorum, Alternaria brassicicola). The growth was limited when ethoxylated isodecyl alc. was added to the active ingredients. The addn. of the rapeseed oil Me ester resulted in a decrease in the fungicidal activity of the agents.