Department of Pesticide Regulation

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June 8, 2001   ENF 2001-027
County Agricultural Commissioners  



This letter interprets the status of phosphorus acid and whether certain uses (e.g., Sudden Oak Death (SOD)) fall under the jurisdiction of pesticide or fertilizer laws. The example brought before us involves the use of phosphorus acid by tree injection to oaks infected or showing symptoms of SOD. We recognize that the impact of SOD can be devastating and the control strategies are limited, however, the search for treatments must be conducted within the confines of current law.

The issue of phosphorus acid used as a pesticide, and the associated nutritional claims, dates from the early 1980's. There are two Enforcement Letters, 87-114 and 88-4, addressing use of phosphorus acid in avocados as a fungicide to control phytophthora. The application method (tree trunk injection) and the nutritional claims made for this product are the same for avocados with phytophthora as oak trees infected with SOD.

Phosphorus acid is currently registered with the U.S. Environmental Protection Agency (U.S. EPA) and the Department of Pesticide Regulation (DPR) as a pesticide. The California Department of Food and Agriculture (CDFA) has reviewed specific labels for phosphorus acid products to be certain that they are in compliance with labeling requirements pursuant to Title 3 California Code of Regulations, Division 4, Chapter 1, subchapter 1, Article 1, Section 2303.

CDFA has authority over phosphorous acid products sold in California as fertilizers. Their determination governs the continued use of these fertilizer products. CDFA concurs that phosphorus acid when applied to soil, slowly converts to phosphate, the only nutritionally active form of phosphorus. CDFA has not evaluated tree trunk injection of phosphorus acid (phosphite). CDFA has no data on file to support nutritional claims made for this application method. Questions concerning the nutritional value of phosphorus acid applications should be directed to CDFA, Agricultural Commodities and Regulatory Services. Any attempts to regulate phosphorus acid products when claims are limited to nutrition and not pesticidal would have to be based on a clear determination that there is no nutritional benefit and they are therefore fraudulent.

DPR has authority over phosphorus acid products sold or used as pesticides, or, intended for pesticidal purposes in California, regardless of their fertilizer status with CDFA. Registration with U.S. EPA and DPR is required for any pesticidal use. Phosphorus acid fertilizer products cannot be represented as pesticides or be sold with written or oral claims to that effect unless registered. There are currently several phosphorus acid compounds registered as pesticides. Any violations of this requirement would be subject to enforcement actions by DPR or the county agricultural commissioners.

Over the years, DPR has been very consistent in its interpretation of when phosphorus acid and other "fertilizers" become pesticides. If the intention, claim or use is pesticidal, the product must be registered for that use. This includes other fertilizers, such as, CAN 17, calcium nitrate, etc. which may also be used as pesticides. Examples of this requirement include the minerals in fertilizers such as zinc, copper, and/or sulfur which may also be the active ingredient in fungicides; these products may require registration as pesticides based on their intended use.

Enforcement action against the illegal claims, intent, or use of unregistered pesticide products should be based on solid investigations and case files. Additionally, you may consider the possibility of proving fraud, based on unsubstantiated claims, through your local District Attorney. Please refer any unregistered pesticide products, or any further questions to your county Senior Pesticide Use Specialist. Any questions concerning he plant nutrient properties of phosphorous acid or other fertilizers should be directed to Mr. Steve Wong, Branch Chief, Agricultural Commodities and Regulatory Services Branch, CDFA, at (916) 654-0574.

Original Signature by:
Scott T. Paulsen, Chief
Pesticide Enforcement Branch
(916) 324-4100


cc:  Mr. Daniel J. Merkley, Agricultural Commissioner Liaison
      Mr. Steve Wong, CDFA