AbstractChanges in the relative importance of the fungi attacking blackcurrants have possibly been due, in part, to the replacement of lime sulphur for insect control. The dwarfing due to sulphur can also be induced by the use of (2‐chloroethyl)‐trimethylammonium chloride or N‐dimethylaminosuccinamic acid, and these chemicals may also affect the incidence and severity of certain fungal diseases. While some growth regulators may be generally beneficial in reducing infection, the results are unpredictable, and the effects are examined in the light of other ways in which host resistance may be altered.