1. (a) Products that contain phosphorous acid shall state on the label the percentage of “Total Phosphoric Acid”, upon conversion of phosphorous acid.

   1. (1) “*Phosphorous acid products are for use as a supplemental fertilizer treatment.
   2. (2) Upon foliar application, the phosphite ions are taken up directly by the plant foliage and may undergo a degree of conversion to phosphate ions, or will be used directly by plants, as phosphite ions.

   3. (3) As a soil application to annual crops, a lesser response from the initial crop, with a corresponding superior response from succeeding crops, may be observed. In addition, placement close to seeds or root zones may be injurious to crops. The effect may be aggravated by a soil pH below 6.5.

      1. (A) The grade of a product containing phosphorous acid shall either possess an asterisk by the available phosphoric acid percentage expressed as total phosphoric acid (X--X*--X) or it shall represent the amount of guaranteed available phosphoric acid (“0”, if no available phosphoric acid is guaranteed). The asterisk from the grade shall also appear in front of the statements described in subsection (1).

   Total Phosphoric Acid (P₂O₅)

   __________%

   In addition, the label shall state the following:

2. (b) Products that contain both phosphoric acid and phosphorous acid shall state on the label the percentage of “Available Phosphoric Acid” and “Total Phosphoric Acid”. The percentage of “Insoluble Phosphoric Acid” (Citrate-Insoluble Phosphorus), if greater than zero, must be stated immediately below, Ffor example:

   Available Phosphoric Acid (P₂O₅)

   __________%

   __________% Total Phosphoric Acid (P₂O₅)

   __________% Insoluble Phosphoric Acid (P₂O₅)

Note: Authority cited: Sections 407, 14502 and 14631, Food and Agricultural Code. Reference: Section 14631, Food and Agricultural Code.

History

1. Repealer and new section filed 8-2-91; operative 8-2-91 pursuant to Government Code section 11346.2(d) (Register 92, No. 7).

2. New subsections (a)-(a)(3) and redesignation and amendment of existing section as subsection (b) filed 11-6-2003; operative 12-6-2003 (Register 2003, No. 45).

3. Amendment of subsection (a) and new subsection (a)(3)(A) filed 9-29-2022; operative 1-1-2023 (Register 2022, No. 39).

4. Amendment filed 11-14-2025; operative 11-14-2025 pursuant to Government Code section 11343.4(b)(3) (Register 2025, No. 46).