Controlling powdery mildew (Sphaerotheca mors-uvae) of gooseberry (Ribes uva-crispa) with potassium bicarbonate and risk of phytotoxicity

Powdery mildew (Sphaerotheca mors-uvae) severely infects young shoots, stems and fruits of gooseberry (Ribes uva-crispa). Environmental friendly and biological control measures are being sought throughout the world. Especially in organic currant growing effective control measures are needed, because powdery mildew infections may result in a total loss of the crop. In organic currant growing the number of adequate control methods is very limited. Sulphur as a fungicide against powdery mildew in e.g., gooseberry or table grape growing is not recommendable due to possible bleaching of berries and scorching of tender shoots. Various bicarbonate salts are suggested as a good option to control powdery mildew. In a series of experiments the effect of potassium bicarbonate (formulated and unformulated products) on powdery mildew of gooseberry was evaluated. In the trials different strategies were tested; i.e., preventive and curative strategies. The percent of infected berries, shoots and disease severity were assessed. Very high disease incidences were observed in the untreated control. All potassium bicarbonate treatments significantly reduced the powdery mildew severity in leaves and fruits compared to the untreated controls. The preventive strategies were very successful. However, the number of spray applications was high. Frequently, a severe phytotoxicity caused by potassium bicarbonate was observed. Several experiments were performed with different dosages, timing of sprayings and spray intervals. The potential and limitations of potassium bicarbonate used to control powdery mildew in the field are discussed.