Potassium Bicarbonate as a Potential Sulphur Substitute in Protected Organic Cropping

Summary in the original language of the document

Powdery mildew attacks several important crops in greenhouses (e.g. tomatoes, cucumbers). Compared to other airborne pathogens, such as downy mildews (e.g. Pseudoperonospora cubensis or Phytophthora infestans) or Botrytis, the damage is often not very severe. However, an effective control of powdery mildew with organic fungicides gives the possibility to optimize climate conditions to also prevent downy mildews and gray mold. Sulphur, a well established fungicide, is rated as slightly to very harmful to beneficial organisms (Koppert Biological Systems, 2010) and may have a phytotoxic effect on some crops (e.g. melon). Effects of potassium and sodium bicarbonate (baking soda) against diseases are well known (Horst et al., 1992). In 2008, the European Commission authorized the use of potassium bicarbonate in organic agriculture (EC, 2008). In this study, the effects of a formulated potassium bicarbonate product, Armicarb® were tested against powdery mildew on tomato, cucumber, melon, rosemary, sage and corn salad. The disease-reducing effect of potassium bicarbonate was comparable to sulfur for most of the tested crops. With protective applications, the efficacy was higher than 90%. However, in melon, where powdery mildew was present before the first spray was applied, efficacy was only 74%. Compared with plant oils or extracts (such as fennel oil, tea tree oil and lecithin), potassium bicarbonate has shown the same or better efficacy. In our experiments, we found no phytotoxicity caused by the potassium bicarbonate product Armicarb®.