Material name: Bicarbonate (Potassium or Sodium)

Material type: mineral

U.S. EPA Toxicity Category: III, "Caution"

USDA-NOP:
Considers sodium bicarbonate as nonsynthetic and allowed. Potassium bicarbonate is considered synthetic and is permitted for plant disease control. The related chemical ammonium carbonate is permitted only for use as bait in traps for insect control. Organic crops destined for export to Japan may not be produced using potassium bicarbonate. (NOP 2000).

Material description:
These products rely on a bicarbonate salt (usually potassium bicarbonate) as the active ingredient. They are promoted for use against powdery mildew diseases. The use of baking soda (sodium bicarbonate) as a fungicide is not a new idea. In Alfred C. Hottes’ A Little Book of Climbing Plants, published in 1933, mention is made of using one ounce of baking soda per gallon of water to control powdery mildew on climbing roses. The author credits the idea to a Russian plant pathologist, A. de Yaczenski (Williams and Williams 1993).

How it works:
According to the Kaligreen® product label, these products disrupt the potassium or sodium ion balance within the fungal cell, causing the cell walls to collapse. Studies to identify the exact mode of action are on-going.

OMRI LISTED PRODUCTS:

Kaligreen® (Arysta Life Science Corp.)
MilStop® Broad Spectrum Foliar Fungicide (BioWorks, Inc.)

References to OMRI listed products in this Guide are based on the June 2004 edition of the OMRI Brand Name List. Please consult www.omri.org for changes and updates in the brand name product listings.

Non OMRI-listed:

Armicarb 100 (85% potassium bicarbonate)
Remedy® (Bonide)
FirstStep®
Bi-Carb Old Fashioned Fungicide®
Note: Baking soda (sodium bicarbonate) cannot legally be used as a pesticide unless it is an ingredient in an EPA registered product.

Formulations and Application guidelines:
Kaligreen is 82% potassium bicarbonate and 18% surfactants and other inerts. The potassium bicarbonate is micro-encapsulated. It is used at rates of 1-5 lb/acre. The pH of the spray solution should be kept at 7.0 or above. Bicarbonate products may be phytotoxic if used at rates above 5 lb/acre. Several studies have shown much better efficacy against powdery mildew when oils are added to bicarbonate products, typically at the rate of 0.5-1.0% (Kuepper et. al. 2001, Ziv and Zitter 1992).

Reentry interval (REI) and pre-harvest interval (PHI):
The EPA Workers Protection Standard requires a minimum of 4 hours before reentering treated areas for Kaligreen®, one hour for Milstop®. There is usually a one day to harvest PHI requirement.

Availability and Sources:
Available through several mail order suppliers.

Effect on the environment:
The active ingredient is a salt of two ions that are very common in nature. It is non-flammable and not considered to be a carcinogen. Neither the active ingredient nor its decomposition products (potassium ions and bicarbonate or carbonate ions, water, or carbon dioxide) have chronic toxic effects. The effects of the inert ingredients are unknown, but in order to meet NOP requirements, approved formulations must be on the EPA list 4, “inerts of minimal concern”.

Effect on human health:
The oral LD50 of Kaligreen is 3358 mg/kg for rats (Labels 2004: Kaligreen MSDS); that of Armicarb is 2700 (Labels 2004: Armicarb MSDS). The Federal EPA ruled (as of December, 1996) that sodium and potassium bicarbonates are exempt from residue tolerances. This action served to facilitate the development and release of commercial bicarbonate products for horticultural use (Kuepper et al. 2001). Sodium bicarbonate has been a component of many foods, and widely consumed over hundreds of years.

Types of pests it controls:
A summary of recent field bicarbonate product efficacy trials on vegetables and fruit commonly grown in the Northeast was compiled for this fact sheet. These university-based trials typically test products with untreated buffer rows and other conditions that create unusually severe pest pressure. The level of pest control is likely to be higher on completely sprayed fields in which a good program of cultural controls has been implemented. Furthermore, many of these trials were implemented without adding oil or other adjuvants to the spray mixture, which might improve efficacy.

In the discussion below, “good control” means statistically significant reductions in disease severity or damage of 75% or more, compared to an untreated control. “Fair control” includes those with significant reductions of 50-74%, and any non-significant reductions of over 50%. The “poor control” group includes any results with less than 50% reduction.
Bicarbonate products give at least partial control of many powdery mildew diseases. Powdery mildews have a more superficial nature on the plant surface that may allow more contact with the product. Many other diseases do not appear to be affected by bicarbonate products, perhaps because they penetrate deeper into plant tissues. However, in some studies, potassium bicarbonate has given good control of other diseases such as black rot and Phomopsis on grapes and strawberry leaf spot.

Among the 68 recent studies reviewed for this fact sheet, bicarbonate products gave only poor results against some diseases. These included anthracnose and Phomopsis on blueberry, brown rot and leaf spot on cherry, Botrytis on grapes and strawberries, potato late blight, downy mildew on pumpkins, Phytophthora on squash, and powdery mildew on strawberry.

With these results removed from the data set, 39 studies remained, on the pest species against which bicarbonate products showed some potential. The efficacy of different products was compared over these 39 studies. Armicarb 100® gave good results in 28% and fair results in 44% of the studies in which it was used. Kaligreen® showed 9% good and 9% fair results. Since the difference between the two products would appear to be mostly due to ingredients besides the potassium bicarbonate active ingredient, obtaining better results with the OMRI-approved Kaligreen product may depend on the farmer adding sticker-spreaders (and oil, as mentioned above). When pure baking soda or potassium bicarbonate was used, the results also showed some efficacy.

References
Hottes, Alfred C. 1933. A Little Book of Climbing Plants. A.T. De La Mare Co., New York.

Labels 2004: Kaligreen and Armicarb labels available online at: http://www.cdms.net/manuf/default.asp Milstop label: http://www.bioworksinc.com/

Kuepper, G., R. Thomas, and R. Earles. 2001. Use of Baking Soda as a Fungicide. Appropriate Technology Transfer to Rural Areas (ATTRA) http://attra.ncat.org/attra-pub/bakingsoda.html

NOP. 2000. USDA National Organic Program regulations, 7CFR 205.206(d)(2), 205.601(c)(1), 206.601(i)(8) http://www.ams.usda.gov/nop

Williams, G. and P. Williams. 1993. Baking soda vs. powdery mildew: Not a new idea! HortIdeas. June. p. 62.

Ziv, O. and T. A. Zitter. 1992. Effects of bicarbonates and film-forming polymers on cucurbit foliar diseases. Plant Disease. Vol. 26, No. 5. p. 513-517.