Many readers have expressed interest in using potassium bicarbonate or sodium bicarbonate as preventive fungicides. As a result, we have devoted several articles (Issues 2 and 3 in 1997 and Issue 9 in 1998) to this topic but have been unable to provide information about legal and available products or about how well the products might work.
Recently, however, I received information about a new product called Remedy, which is a dry formulation containing 82% potassium bicarbonate as the active ingredient. The product is now being marketed by Bonide Products, Inc., and is available to garden centers and other stores carrying the Bonide line of pesticides. A few calls in the Champaign–Urbana area revealed that Remedy is not yet on the shelves.
A little background on the bicarbonates. Although I have not been able to find published research dealing specifically with Remedy, I have found a scattering of articles about sodium, potassium, and ammonium bicarbonates. Most often, these compounds were tested against black spot of rose and various powdery mildew pathogens of ornamentals. Although most of the research indicates that bicarbonates alone reduce disease compared to untreated plants, it also indicates that addition of a horticultural summer oil does a much better job. What are the drawbacks to these products and the published research? First, the mixing rate is critical because even a small change in spray concentration can lead to reduced control (lower concentration) or plant damage (higher concentration). Second, the bicarbonates are seldom compared to available, conventional fungicides so at this point it is impossible to say that Remedy is more or less effective than products currently being used.
The Remedy label states that it controls black spot, downy mildew, powdery mildew, botrytis blight, scab, and a variety of other foliar diseases. It is labeled for use on many woody and herbaceous ornamentals and for many garden plants. As mentioned above, the bicarbonates tend to work much better when used with a horticultural summer oil. However, the Remedy label clearly states: “Do not mix with other pesticide products or spray adjuvants.” This appears to be a problem. However, I spoke with a technical representative who assured me that the Remedy formulation contains a dry spreader/sticker, which provides an increase in effectiveness similar to that reported in the literature.
Even though the active ingredient for Remedy (potassium bicarbonate) is considered to be relatively nontoxic (source: MSDS sheet, Cornell University), it is still a pesticide and must be used responsibly and with respect. As with all pesticides, remember to read and follow all label precautions, directions, and other instructions.