Using Potassium Bicarbonate Against Powdery Mildew

Technical articles - Diseases

Market gardening Market gardening Viticulture Viticulture

Chemical formula of potassium bicarbonate

Potassium bicarbonate with the potassium chemical formula KHCO₃, also called potassium hydrogen carbonate, appears as a slightly translucent white powder that tends to clump with moisture. Potassium bicarbonate is a biodegradable, non-toxic, and economical product, effective in the preventive fight against pathogenic fungi of crops, notably downy mildew and powdery mildew.

Mode of action of potassium bicarbonate

Potassium bicarbonate acts as a contact fungicide. It is effective on outdoor or greenhouse crops against aerial fungi. The mycelia of these fungi develop on the surface of plant tissues and are particularly exposed.

The mode of action of potassium bicarbonate involves several factors:

• Effect of the product's pH (pH of potassium bicarbonate = 8.2) neutralizing the acidity of an environment, a necessary condition for the development of downy mildew and powdery mildew.
• Disruptor of the fungal cell membrane's integrity and balance, it causes rupture of the cell membrane and cell death.
• Enzymatic inhibition, inhibition of mycelium development and spore germination.
• Disruptor of osmotic pressure, pH, and effects of bicarbonate/carbonate ions.
• Stop effect by drying out the pathogen present on the plant surface.

The modes of action of potassium bicarbonate provide it with curative and preventive properties. The pathogen is spread by contaminating rains; potassium bicarbonate being a highly water-soluble active substance, its preventive efficacy depends on several factors including wash-off resistance. The protection duration is 7 to 10 days preventively versus 1 to 2 days curatively.

Application of potassium bicarbonate

• Dose: maximum 0.5% potassium bicarbonate in the spray mixture.
  • 1.1 kg/ha to 5.6 kg/ha (dose not to exceed).
  • 400 to 2000 liters of spray mixture/ha depending on leaf density.
• Preparation of the spray mixture: pH of the solution above 7, check mixing compatibilities (copper, alkaline solutions...)
• Potassium bicarbonate leaves no visible residues on plants.
• Important repetition of treatments: 3 to 4 applications at intervals of five to seven days when conditions favor fungal development or at the first appearance of symptoms. Shorten the application interval during rainy periods and high relative humidity.
• As the product acts by contact, spraying must cover the entire plant surface.
• Use the phytosanitary spray mixture immediately after preparation.

The quality and application conditions are essential for treatment success. Potassium bicarbonate must be used as part of a global protection strategy against powdery mildew, integrating prophylaxis, other biocontrol methods, and the use of conventional fungicides.

Benefits

• The main advantage of bicarbonate is that it is non-toxic. The decomposition of potassium bicarbonate produces potassium carbonate, water, and carbon dioxide. These products dissipate rapidly in the environment, making it a recommended product in sustainable agriculture.

• No resistance phenomena.
• Shock effect upon product application.

• The re-entry interval of 6 hours and pre-harvest interval of 1 day facilitate use in protected cultivation and on continuously producing crops.
• This active substance is free of MRLs, making it interesting in quality approaches such as " zero residue " or other sector specifications.

Limitations

• Potassium bicarbonate must be sprayed weekly to provide good control.
• It can cause phytotoxicity on certain species when used at concentrations higher than 0.5%.

• An increase in soil bicarbonate levels can lead to deficiencies (iron, calcium...).

• Insufficient efficacy if disease pressure is high.

• This solution may require more applications than a conventional solution, and greater vigilance regarding spray quality.
  

Cost

The cost of using potassium bicarbonate averages €35-45 per hectare treated for powdery mildew (the average cost of a fungicide treatment is €37/ha against powdery mildew).

However, it is used with the same spraying equipment as conventional fungicides, so no additional application cost.

Commercial substances

Potassium bicarbonate is a basic substance, easily found commercially in raw form.

Many commercial substances are also offered for sale. These are mostly composed of potassium bicarbonate (over 80%) and adjuvants that allow proper product distribution, fixation on the leaf, and prevent the active ingredient from forming large crystals.

Find the list of products composed of potassium bicarbonate here.

Further reading

Feel free to consult these technical datasheets of commercial products:

• Vitisan

• Certis
• Amicarb

Appendices

Est complémentaire des leviers

• Practicing biocontrol using natural substances
• Practicing biocontrol
• Practicing biocontrol in viticulture
• Practicing biocontrol in market gardening
• Alternatives to copper in organic viticulture

S'applique aux cultures suivantes

• Vine
• Tomato
• Zucchini

Défavorise les bioagresseurs suivants

• Powdery mildew
• Powdery mildew of vine
• Downy mildew
• Downy mildew (vine)