Department of Pesticide Regulation

APPLICATION OF NITROGEN-BASED MATERIAL TO DORMANT PLANTS FOR PLANT GROWTH REGULATING EFFECTS

This letter clarifies current Department of Pesticide Regulation (DPR) application of the law to the use of nitrogen-based materials during dormant season on trees and vines.

DPR's interpretation is that materials applied directly to or "over the top" of dormant vines or trees to stimulate bud break are being used as a plant growth regulator (PGR) regardless of the product's status as a registered fertilizing material with the California Department of Food and Agriculture, and must be registered as a pesticide (see Pesticide Registration Branch letter PRB 97-51, enclosed). It is not necessary that the manufacturer make specific PGR claims for the product. Enforcement letter ENF 2000-02 was not intended to limit the general policy to any specific product.

Based on DPR's scientific review of University of California literature concerning the use of nitrate-containing fertilizers, the use of CAN, UAN, potassium nitrate, or other materials to break buds is analogous to the use of hydrogen cyanamide, both in intent and mode of action. Specifically, DPR does not agree that the fertilizer products are acting as "nutritional bud-breaking agents." The scientific evidence indicates that (1) nutrition does not break buds and (2) the nitrogen fertilizers are acting through physiological means to break bud dormancy and are PGRs. Questions concerning the scientific literature relative to PGRs versus fertilizers and dormancy can be directed to Dr. Don Koehler of DPR's Pesticide Registration Branch at (916) 324-3950 or at e-mail dkoehler@cdpr.ca.gov.

The integrity of the pesticide regulatory program dictates that we not ignore this issue. We can recommend education and outreach to industry for the balance of this growing season. In the future, this use pattern should be given appropriate priority and integrated into your overall pesticide use enforcement program, recognizing that current data indicate that calcium cyanamide more closely approaches the worker safety and environmental hazards of hydrogen cyanamide than other commonly used materials. If you see a need to make this a focused activity in your county, you should discuss this with your liaison Senior Pesticide Use Specialist for the next negotiated workplan.

If you have any questions, please contact the liaison Senior Pesticide Use Specialist serving your county.

cc:  Mr. Steve Wong, CDFA (w/Enclosure)
      Mr. Daniel J. Merkley (w/Enclosure)
      Dr. Don Koehler (w/Enclosure)