Control of apple scab (Venturia inaequalis) with bicarbonate salts under controlled environment

The effectiveness of potassium bicarbonate against Venturia inaequalis, the cause of apple scab, was studied. In vitro experiments with sodium, ammonium and potassium bicarbonate, as well as potassium phosphate used at 1% (w/v), reduced colony growth of V inaequalis by 99, 98, 90 and 64%, respectively. Under controlled conditions in greenhouse experiments, a single spray of 0.5 or 1% (w/v) aqueous solution of sodium or potassium bicarbonate applied on young apple seedlings, 24 h before or 24 h after scab artificial inoculation, significantly controlled the disease. Greater effectiveness of potassium bicarbonate was recorded when the period of time before or after the inoculation was reduced. A significant increase of the fungicide activity of potassium bicarbonate was observed when salt was mixed with mineral oils. However, combining potassium bicarbonate with vegetable linseed oil and grapefruit seed extract did not increase its efficacy whereas these two vegetable products used alone reduced significantly scab infections. Formulated potassium bicarbonate, under the trade name Armicarb((R)) 100 and containing surfactant compounds, was more effective than bicarbonate alone. A phytotoxicity effect of potassium bicarbonate was observed with a 0.75% dose. The potential and limitations of potassium bicarbonate used to control apple scab in the field are discussed.