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How the maps were made

The pesticide-use maps provided on this web site show the geographic distribution of estimated use on agricultural land in the conterminous United States for numerous pesticides (active ingredients). Maps were created by allocating county-level use estimates to agricultural land within each county. A graph accompanies each map, which shows annual national use by major crop for the mapped pesticide for each year. 

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).  Two different methods, EPest-low and EPest-high, were used to estimate a range of use, with the exception of estimates for California, which were taken from annual Department of Pesticide Regulation Pesticide Use Reports (Thelin and Stone, 2013).

EPest-low and EPest-high methods

Both EPest-low and EPest-high methods incorporate proprietary surveyed rates for United States Department of Agriculture Crop Reporting Districts (CRDs), but EPest-low and EPest-high estimates differ in how they treated situations when a CRD was surveyed and pesticide use was not reported for a particular pesticide-by-crop combination. If use of a pesticide on a crop was not reported in a surveyed CRD, 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) to understand the details of how both estimates were determined. Maps are provided for both EPest-low and EPest-high estimates.

Pesticide use dataset

The companion county-level pesticide use dataset Estimated Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 1992–2009(Stone, 2013) was used to create the maps. County-level estimates of total agricultural use for each pesticide were allocated to agricultural land within each county, as defined in the 2009 Cropland Data Layer (CDL) developed by the United States Department of Agriculture, National Agricultural Statistics Service (Johnson and Mueller, 2010). Individual crop types in the CDL raster dataset were reclassified to simply differentiate agricultural land (including pasture and hay) from non-agricultural land. The CDL was then generalized to one square kilometer cell size and the percentage of agricultural land for each cell was calculated. The proportion of county agricultural land included in each one 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, all of the cell values nationwide for the entire period were divided into quintiles and a color-coded map was generated for each year; the quintile classes were converted to pounds per square mile. 

Use-Trend Graphs by Crop

Graphs showing annual use by crop for each pesticide were created by summing the national pesticide use for each compound, for each crop or combination of crops. Combined crops are Pasture and Hay (alfalfa, cropland for pasture, fallow and idle cropland, pastureland,  and other hay); 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 and Cropland Data Layer Crop Names are shown in the following table.

Applications and limitations

Pesticide use estimates from this study are suitable for making national, regional, and watershed assessments of annual pesticide use, however the reliability of estimates generally decreases with scale.  For example, detailed interpretation of use intensity distribution within a county is not an appropriate use.  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. 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), the maps, graphs, and associated county-level use data are critical data for water-quality models and provide a comprehensive graphical overview of the geographic distribution and trends in agricultural use in the conterminous United States.

References 

Johnson, David, and Mueller, Richard, 2010, The 2009 Cropland Data Layer: Photogrammetric Engineering and Remote Sensing, v. 76 no. 11, p. 1201- 1205.

Stone, W.W., 2013, Estimated annual agricultural pesticide use for counties of the conterminous United States, 1992–2009: U.S. Geological Survey Data Series 752, 1-p. pamphlet, 14 tables.

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.

Stone, W.W., 2013, Estimated annual agricultural pesticide use for counties of the conterminous United States, 1992–2009: U.S. Geological Survey Data Series 752, 1-p. pamphlet, 14 tables.

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