Department of Pesticide Regulation

Environmental Monitoring and Pest Management Branch

830 K Street

Sacramento, CA 95814-5624

Identifying Types and Locations of Non-crop Preemergent Herbicide Applications in Fresno and Tulare Counties, California.

STUDY #180

February 1999


The preemergent herbicides simazine and diuron are the most common currently registered pesticides detected in California's ground water. Most detections are in Fresno and Tulare Counties where 412 and 311 confirmed detections of simazine and diuron, respectively, have been reported. Simazine and diuron are applied to a variety of crop sites, including citrus, grapes, olives and nutcrops. The two herbicides are also widely used for weed control in non-crop sites such as railroad and highway rights-of-ways (ROW), ditchbanks, and along county roads. Of the approximately 590,000 lbs of simazine and diuron active ingredient applied in Fresno and Tulare Counties in 1995, 88,000 pounds - about 15 percent - were applied to non-crop sites.

California has had mandatory pesticide use reporting since 1990. The Department of Pesticide Regulation (DPR) maintains the annual pesticide use report (PUR) databases. The databases contain a variety of information about pesticide applications, including type of crop or site, date of application, and location of crop applications according to the meridian/township/range/section (MTRS) convention. This site and location information is invaluable for understanding the relationship between pesticide applications and subsequent detection in ground water, leading eventually to development of mitigation measures to prevent further ground water contamination.

In the case of ROW applications, MTRS data are not reported in the PUR. This is particularly important for simazine and diuron because of the uncertainty about the respective contributions of crop vs ROW applications to detections in ground water. In addition, no distinction between different ROW application sites (highways, railroads, etc.) is made in the PUR. This lack of information contributes to our inability to determine the potential contribution of ROW herbicides to ground water contamination. As a result, effective mitigation measures for ROW sites are difficult to develop. The purpose of this study is to investigate the types and locations of ROW applications in Fresno and Tulare Counties where ROW mitigation measures may be most needed.


The objectives of this study are to:

(1) Identify the most prevalent types of non-crop and ROW applications of simazine and diuron based on total use,

(2) Determine the geographic locations of such applications, and

(3) Characterize the potential for off-site movement of herbicides at selected representative ROW application sites.


This study will be conducted by the Environmental Hazards Assessment Program (EHAP) under the general direction of Don Weaver, Senior Environmental Research Scientist. Key personnel are listed below:

Project Leaders: Frank Spurlock, Cindy Garretson

Field Coordinator: Cindy Garretson

Senior Staff Scientist: John Troiano

Questions concerning this study should be directed to Mark Pepple at (916) 324-4086, facsimile (916) 324-4088.


This study will be conducted in two phases. Phase one will involve gathering information and data about ROW/non-crop applications in Fresno and Tulare Counties. This information will include, but not be limited to, answers to the following questions:

1. Who are the greatest users of ROW herbicides?

2. Where do most of the ROW applications take place?

3. How much of this use is in agricultural areas?

4. What types of best management practices, if any, have different users developed?

5. What application rates are being used in different scenarios?

Additional questions/data needs will be developed during this portion of the study. Information sources for these questions may include, but are not limited to, Fresno and Tulare County Agricultural Commissioner's records, CalTrans personnel, county personnel, railroad companies, commercial applicators, irrigation districts, etc.

Phase two will consist of locating and characterizing "representative" ROW application sites. The number and location of these sites will depend on the results from phase one of this study. Depending on the sites selected, a variety of data may be collected. This may include, but not necessarily be limited to, the following:

soil type

depth to ground water

soil infiltration rate

drainage area

simazine and diuron soil residue concentrations (FY99-00)

presence and type of vegetation

concentration of simazine and diuron in runoff water (FY99-00)

application history

size of treated area

location and method of drain water disposal


The results from this study will be detailed in an EHAP report or memorandum, and will also be used to determine the possible need for, and types of potential ROW/non-crop herbicide application mitigation measures to protect ground and/or surface waters.

The projected timeline for this project is as follows:

Start date: February, 1999

site selection: fall/winter, 1999

sampling: winter/spring 2000

report completion: summer 2000