111ORIGINAL SCIENTIFIC PAPER Summary

Th e eff ect of covering the crop with polythene tunnels on Botrytis fruit rot was investigated. Two cultivars were grown organically in three fi eld experiments during 2001-2003. Botrytis cinerea is a major threat to strawberry cultivation in the fi eld, especially when the crop is grown organically. Control of the disease in organic strawberry crops depends merely on prevention. Botrytis infection risk depends on humidity and temperature. Under optimal temperature conditions leaf wetness period necessary for infection of strawberry fl owers decreases (Bulger et al., 1997). Prevention or shortening of the leaf wetness period might help to reduce infection risk of strawberries. Cv. Elsanta proved less susceptible to B. cinerea than cv. Darselect, thus choosing an appropriate cultivar is a helpful means to control grey mould. Covering the crop with polythene tunnels eff ectively reduced the infection risk of B. cinerea on strawberry fl owers. Mechanisms to regulate the temperature in the tunnel are necessary to ensure fruit quality and should be investigated further. Key words Fragaria x ananassa Duch., cultural control, infection ris