Phosphorous Acid (H3PO3)

Last updated: November 19, 2021

What Does Phosphorous Acid (H3PO3) Mean?

In gardening, phosphorous acid is commonly used to prevent and treat various types of fungus-related diseases. Growers tend to favor phosphorous acid because it has a unique mode of action and is known to be much less expensive than other types of fungicides.

Aliette, Agri-Fos, Phostrol, and ProPhyt are the most popular types of phosphorus-based fungicides on the market.


Maximum Yield Explains Phosphorous Acid (H3PO3)

Studies have shown that spraying grapes with phosphorous acid every two weeks can both prevent and control downy mildew.

Phosphorous acid has also been known to protect plants against extreme humidity in rainy weather. While there have been some concerns about acid burns on the leaves, research has shown that wine grapes such as ‘Blanc Du Bois’ and ‘Lenoir’ could easily sustain phosphorous acid of up to 0.65 percent with no damage to the leaves. However, a concentration of 1.0 or more can cause severe damage to the plants.

Along with being an excellent fungicide, phosphorous acid can additionally encourage the plants to produce new tissue while boosting cell growth and enlargement. Phosphorus deficiency can create a severe imbalance in plants as it causes stunted growth.

Note that phosphorous acid and phosphoric acids are very different. Phosphorous acid, which has one less oxygen molecule (H3PO3) is used as a fungicide in diluted form. It is generally sold in salt form, but some liquid mixtures are available. Phosphoric acid, on the other hand, is a mineral acid used in a wide range of applications, including plant fertilizer, where it forms the “P” in the N-P-K rating.


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