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Pesticide Information

Identifying Agricultural Management Practices to Reduce Pesticide Runoff

The Situation

Organophosphate (OP) pesticides, especially diazinon and chlorpyrifos, have been routinely detected in water-quality monitoring projects coinciding with flooding of dormant orchards by winter rains in the Sacramento River and San Joaquin River watersheds. These studies, conducted by both federal and state agencies, indicate that small invertebrates are killed when exposed for even short periods to the OP levels measured in the two watersheds during the winter. These invertebrates are indicators of the health of aquatic food chains and serve as primary food for many larval and juvenile fish.

Published and unpublished data reveal that one source of the OPs detected in tributaries and rivers is rain runoff from orchards. The magnitude and duration of the insecticide-caused toxicity following winter storms led the Central Valley Regional Water Quality Control Board to declare this a violation of its Basin Plan water quality standard for toxicity.

In 1998, the State of California placed the Sacramento River and the San Joaquin River, as well as the associated Delta/Estuary, on the Clean Water Act 303(d) list of impaired waterways, partly because of elevated levels of diazinon and chlorpyrifos, presumed to originate at least in part, from dormant spray orchard runoff. These listings necessitate the development of specific restrictions on the quantities of the OPs that can be allowed in surface waters (Total Maximum Daily Loads, or TMDLs). Diazinon and chlorpyrifos are widely used in California for a variety of urban as well as other agricultural applications, and all uses are subject to restrictions stemming from the TMDL limitations. Additionally, OPs, in general, are primary targets of the Food Quality Protection Act of 1996 (FQPA).

Identifying agriculture's contribution to the problem is just one part of the issue. Its resolution requires understanding the specific agricultural production practices and the urban uses related to the problem, the mechanisms of off-site movement of pesticides, and developing alternative practices to reduce pesticide runoff to a level that eliminates toxicity in surface waters.

The best solutions to these issues will be those that evolve from a solid information base coupled with input from the users of pesticides, including growers, landscape managers, urban and suburban residents, and the agencies charged with maintaining water quality.

The Role of the University

Acting on a grant from the CALFED Bay-Delta Program, former Statewide IPM Program Director Frank Zalom has been coordinating a multi-disciplinary team that includes: Dr. Inge Werner, Aquatic Toxicology Laboratory, UC Davis School of Veterinary Medicine; Dr. Barry Wilson, UC Davis Department of Animal Science and Department of Environmental Toxicology; Dr. Wes Wallender, Department of Land, Air, and Water Resources; and Dr. Ken Giles, Department of Biological and Agricultural Engineering. Through September 2002, Mike Oliver, UC IPM, served as the team’s program manager. Steering committees, comprised of representatives from state agencies, grower groups, and local UC Cooperative Extension offices, provide direction for the projects.

One of their initial tasks was to provide detailed assessments of the current knowledge of alternative agricultural practices for reducing or eliminating pesticide use, particularly as it pertains to orchard crops and specifically as it pertains to the use of organophosphate (OP) dormant sprays. They issued a report in September of 1999 that outlined a number of viable alternatives to traditional OP dormant sprays for a variety of orchard crops. The report also contained an economic analysis of costs associated with the various alternatives. Although the alternatives can be somewhat more complex to administer and their costs can run higher than that of OP sprays, the report noted that the increased cost, relative to the total cost of production, was not large.

Building on the economic analysis of the report, Statewide IPM Program staff constructed a Web-based calculator for alternative practices that went online in January 2000. The Dormant Spray Alternatives Calculator can be used by growers and others interested in comparing costs associated with various alternatives. Users can choose to accept default cost values for production parameters (for example, pesticide used, rate of application, method of application, and monitoring costs), or they can enter their own values instead.

In addition to the assessments, the project members developed a number of educational documents and conducted workshops to provide information to growers and pest control industry personnel. Information focused largely on explaining what the problem is, agriculture's role in the problem, and the alternatives available to help eliminate the problem. A number of grower and industry organizations added significantly to the outreach efforts by publishing and distributing newsletters and pamphlets emphasizing the messages coming from the UC efforts.

The UC work has not only successfully produced the products called for in the contract with CALFED, but has also yielded a number of other tools, methodologies, and information that promise to be of value in the overall effort to improve surface water quality throughout the CALFED watersheds of concern. Some of the major UC products/accomplishments include:

  • The information matrices for alternative agricultural practices (orchard production) for reducing the use and impacts of OPs both for dormant season and in-season pest control scenarios.
  • An information matrix for alternative urban practices for reducing the use and impacts of OPs.
  • Presentation of educational and outreach materials for urban and agricultural alternatives via a wide array of meetings and communication media.
  • The development of an online Dormant Spray Alternatives Calculator to assist growers and pest control advisors in comparing the actual costs of viable alternatives to using OP sprays during the dormant season.
  • Publication of detailed information on multi-year usage patterns of OPs relative to other pest control materials throughout the Central Valley region.
  • Active participation with stakeholder groups (e.g., the Sacramento River Watershed Program, the Urban Pesticide Committee, and the Ag Implementation Group—San Joaquin River) and agencies (e.g., the Department of Pesticide Regulation, the Central Valley Regional Water Quality Control Board, and the City of Modesto). The UC products and input have been well received by all of these entities and are considered vital to the accomplishment of their collective goals.
  • A study and report on urban versus agricultural contributions to OP surface water toxicity (the Modesto Report).
  • Development of field monitoring equipment and modeling procedures to allow for the collection of orchard runoff and to account for various hydrological influences that impact runoff.
  • Demonstration sites to elucidate the efficacy of various best management practices in reducing orchard runoff and the associated contamination of surface waters by pesticides.
  • Papers submitted for publication that describe the toxicity data developed by our orchard floor vegetation studies that compared diazinon and esfenvalerate in orchard runoff.
  • Demonstrations of the variations in aquatic species susceptibility to pesticide-caused toxicity, i.e., EPA standard bioassay species versus species native to the CALFED watersheds of concern.
  • A significant investment (labor, travel, and laboratory assistance) in establishing baseline pesticide loading in a sub-watershed that is the focus of a 3-year CWA 319(h) project funded through the Prune Board and supported by the Sacramento River Watershed Program (SRWP).
  • An evaluation of potential spray application technologies that may serve to mitigate the pesticide runoff issue via the amount of pesticide used, more accurate targeting of pesticides, and formulations that enhance efficacy.
Current and Future Goals

The UC program is currently focusing its resources on three main areas:

  • Continuing and strengthening the educational efforts to assist agriculture
  • Conducting field studies to investigate a variety of potential management methodologies for reducing dormant spray runoff from orchards, and
  • Developing methods to better assess the chemical composition and hydrology of orchard runoff.

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