BOČEK, S., SALAŠ, P., SASKOVÁ, H., MOKRIČKOVÁ, J.: Eff ect of Alginure® (seaweed extract), MycoSin®VIN (sulfuric clay) and Polyversum® (Pythium oligandrum Drechs.) on yield and disease control in organic strawberries. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 8, pp. 19-28 In 2011 and 2012 three commercial products Alginure® (seaweed extract), Myco-Sin® VIN (sulfuric acid clay with yeast and plant extracts) and Polyversum® (spores of Pythium oligandrum) were tested in fi eld experiment with strawberry cv. 'Induka' under the conditions of organic growing system. The aim of the study was to determine the eff ect of the preparations on yield, fruit quality and diseases control. The preparations were applied fi ve times during fl owering. We assessed total yield, marketable and unmarketable yields, average fruit weight, grey mould incidence on fruits caused by Botrytis cinerea and leaf spot severity caused by Mycosphaerella fragariae. Effi cacy (%) of preparations was calculated. Preparations did not show positive eff ect on yields parameters. Total and marketable yields were not signifi cantly diff erent to untreated control in both years. Nevertheless considerable increase of yields from 2011 to 2012 was observed in strawberries treated by biofungicide Polyversum®. Preparations did not signifi cantly reduce the incidence of grey mould. Alginure® showed the best results by effi cacy 39.6 % and 57.4 %, respectively. All preparations provided very low, less than 10% effi cacy to control leaf spot severity.