National Water-Quality Assessment (NAWQA) Project
For all States except California, proprietary farm survey pesticide-use data are aggregated and reported at the multi-county Crop Reporting District (CRD) level. Harvested-crop acreage data by county from the U.S. Department of Agriculture Census of Agriculture are used to calculate the median pesticide-by- crop use rates for each crop in each CRD. These rates are applied to the harvested acreage of each crop in a county to obtain pesticide-use estimates at a county level. Estimates for California are obtained from annual Department of Pesticide Regulation Pesticide Use Reports (California Department of Pesticide Regulation). Methods for generating county-level pesticide-use estimates are described in Estimation of Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 1992–2009 (Thelin and Stone, 2013) and Estimated Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 2008-12 (Baker and Stone, 2015).Maps are created by allocating county-level use estimates to agricultural land within each county based on land classifications defined in the National Land Cover Database 2011 (NLCD11) (Jin and others, 2013; NLCD 2011 Data Download). The NLCD11 is used for the entire period of record because at a national level agricultural land use has not changed much during that time frame, and by using a single snapshot in time, changes in pesticide use are not obscured by changes in land use. NLCD11 Planted/Cultivated categories 81 (Pasture/Hay) and 82 (Cultivated Crops) were combined to differentiate agricultural land from non-agricultural land. The NLCD11 was then generalized to 1 square kilometer cell size and the percentage of agricultural land for each cell was calculated. The proportion of county agricultural land included in each 1 square kilometer cell was multiplied by the total county use for each pesticide to calculate the proportional amount of use allocated to each cell. To display pesticide use on the annual maps for each compound, the range of all of the cell values nationwide for the entire period are divided into quartiles and a color-coded map is generated for each year based on these quartiles. The quartile classes are converted to pounds per square mile.
For all States except California, two different methods, EPest-low and EPest- high, are used to estimate a range of pesticide use. Both EPest-low and EPest-high methods incorporate proprietary surveyed rates for Crop Reporting Districts (CRDs), but EPest-low and EPest-high estimates differ in how they treat situations when a CRD was surveyed and pesticide use was not reported for a particular crop present in the CRD. In these situations, EPest-low assumes zero use in the CRD for that pesticide-by- crop combination. EPest-high, however, treats the unreported use for that pesticide-by- crop combination in the CRD as missing data. In this case, pesticide-by- crop use rates from neighboring CRDs or CRDs within the same region are used to estimate the pesticide-by- crop EPest-high rate for the CRD.
State-based restrictions on pesticide use were not incorporated into EPest- high or EPest-low estimates. However, EPest-low estimates are more likely to reflect these restrictions than EPest-high estimates. Users of the maps and data should consult the methods presented in Thelin and Stone (2013) and Baker and Stone (2015) to understand the details of how both estimates were determined. Maps are provided for both EPest-low and EPest-high estimates.Use estimates for California are obtained from annual California Department of Pesticide Regulation pesticide use reports. Because these reports provide county-level use estimates, they are incorporated into the data without further processing and low and high rates are the same for counties in California. California county data are appended after the estimation process is completed for the rest of the Nation.
Graphs showing annual use by crop for each pesticide are created by summing the national pesticide use for each compound, for each crop or combination of crops. Combined crops are Pasture and Hay (cropland for pasture, fallow and idle cropland, pastureland, and other hay); Alfalfa; Orchards and grapes (stone fruit trees, citrus, nut trees, apples, pears, and grapevines); Vegetables and fruit (all vegetables and non-orchard fruit, including beans, peas, greens, berries, and melons); and Other (sorghum, non-wheat grains, tobacco, peanuts, sugarcane, sugarbeets, and other miscellaneous crops). The relations of graphed crops and combinations of crops to individual Epest Crop Names are shown in the following table. State-by crop estimates are available in tabular format.
Pesticide-use estimates from this study are suitable for making national, regional, and watershed estimates of annual pesticide use; however, the reliability of these estimates generally decreases with scale. For example, detailed interpretation of where and how much use occurs within a county is not appropriate. Although county-level estimates were used to create the maps and are provided in the dataset, it is important to understand that surveyed pesticide-by- crop use was not available for all CRDs and, therefore, extrapolation methods were used to estimate pesticide use for some counties. Moreover, surveyed pesticide-by- crop use may not reflect all agricultural use on all crops grown. In addition, State-based restrictions on pesticide use were not incorporated into EPest-high or EPest-low estimates. EPest-low estimates are more likely to reflect these restrictions than EPest- high estimates. With these caveats in mind, including other details discussed in Thelin and Stone (2013) and Baker and Stone (2015), the maps, graphs, and associated county-level use data are critical information for water- quality models and provide a comprehensive graphical overview of the geographic distribution and trends in agricultural pesticide use in the conterminous United States.
Baker, N.T., and Stone, W.W., 2015, Estimated annual agricultural pesticide use for counties of the conterminous United States, 2008-12: U.S. Geological Survey Data Series 907, 9 p., http://dx.doi.org/10.3133/ds907.
California Department of Pesticide Regulation, Variously dated, Pesticide use reporting: California Department of Pesticide Regulation pesticide use reporting (PUR) database, at http://www.cdpr.ca.gov/docs/pur/purmain.htm.
Jin, S., Yang, L., Danielson, P., Homer, C., Fry, J., and Xian, G. 2013. A comprehensive change detection method for updating the National Land Cover Database to circa 2011. Remote Sensing of Environment, 132: 159-175.
Thelin, G.P., and Stone, W.W., 2013, Estimation of annual agricultural pesticide use for counties of the conterminous United States, 1992–2009: U.S. Geological Survey Scientific Investigations Report 2013-5009, 54 p.
U.S. Department of Agriculture, 2014, State and county data, Geographic area series parts 1–50, AC–12–A–1—AC–12–A–50: U.S. Department of Agriculture 2012 Census of Agriculture, v. 1, at http://www.agcensus.usda.gov/Publications/2012