Phosphorous Acid Supplier South Africa | 98.5% Grade H3PO3

What Is Phosphorous Acid?

Phosphorous Acid (H₃PO₃, also written H₂PO₃ in some older literature) is a phosphorus-containing acid with 98.5% purity in the solid (crystal or flake) form. It is distinct from Phosphoric Acid (H₃PO₄) and is not a direct plant-available phosphate fertilizer. Instead, phosphorous acid and its salts (phosphonates) are taken up by plants and stimulate systemic acquired resistance (SAR), activating the plant’s own defence mechanisms against oomycete pathogens such as Phytophthora, Plasmopara (downy mildew), and Pythium.

Phosphorous Acid in Crop Protection

Phosphorous acid is used to manufacture potassium phosphonate (by neutralising with potassium hydroxide), which is one of the most widely used biostimulant/fungicide combination products in fruit and vegetable production globally. Applications reduce the severity of Phytophthora root rot in avocados, downy mildew in grapes and potatoes, and other oomycete diseases. In citrus programs, phosphonate products are widely used as part of integrated management programs. The product must not be confused with phosphoric acid (H₃PO₄), which is a different compound.

Sourcing Phosphorous Acid From Terracore

Terracore supplies 98.5% phosphorous acid in 25 kg bags and drums. We advise on compatibility with potassium hydroxide for phosphonate production, and supply both ingredients. Technical datasheets and SDS are provided with every order.