Strawberry roots containing P. fragariae oospores were immersed for up to 60 d in 1000 micro g/ml captafol, dichlofluanid, fosetyl aluminium and metalaxyl in water and buffer (pH 6.5). Only fosetyl Al in water increased the numbers of dead oospores within roots. Oospores extracted from roots which had been treated with fosetyl Al in water, or metalaxyl in water or buffer, showed reduced infectivity towards strawberry plants and reduced germination on agar without added fungicide. Oospores extracted from untreated roots and placed on agar incorporating the fungicides showed reduced germ-tube production with metalaxyl (3 micro g/ml), captafol (10 micro g) and dichlofluanid (30 micro g). Fosetyl Al (100 micro g) in water but not in buffer agar also reduced germ-tube formation. It is thus inadvisable to treat strawberry nursery stocks with fungicide, because oospores within roots may survive the treatment, while the fungicide residues on the root surfaces could suppress spore germination and infection and so give false negative results when the stocks are tested for red core in root-tip bait tests.