Illinois Fertilizer
Conference Proceedings
January 29-31, 1996
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George F. Czapar1
The effect of agricultural chemicals on water quality continues to be a major public issue. As part of the Safe Drinking Water Act, public water supplies are required to sample quarterly for regulated contaminants, including several pesticides. Maximum contaminant levels (MCLs) have been established for 24 pesticides and four pesticide metabolites. For example, the MCL for atrazine is 3 parts per billion. It is estimated that the total national cost of complying with SDWA drinking water regulations is $1.4 billion annually for public water systems (Auerbach, 1994).
National monitoring studies of surface water quality have helped identify the most common contaminants, and when they are most likely to occur (Goolsby et al., 1991; Thurman et al., 1991). In Illinois, several monitoring programs have examined rivers, streams, and public water supplies (Taylor and Cook, 1995; Ciba Crop Protection, 1995; Temple and Krueger, 1994). Atrazine is often detected in surface water supplies due to its physical and chemical characteristics, and its widespread use. In 1994, atrazine was used on over 80% of the corn acres in Illinois (USDA, 1995).
Wauchope (1978) reviewed the extent of pesticide loss from treated fields due
to surface runoff. Pesticide losses ranged from less than one percent to over
ten percent of the applied product. Numerous studies have shown that chemical
losses are often greatest when heavy rainstorms closely follow pesticide applications.
Best Management Practices (BMPs) are designed to minimize adverse effects of pesticide use on groundwater and surface water quality. In addition to protecting the environment, these practices must be economically sound. In most cases, a combination of BMPs will be required to achieve water quality goals, and the suggested practices may vary depending on soils, topography and individual farm operations.
Integrated pest management (IPM) plays a vital role in protecting water resources. Regular monitoring of crop conditions and pest populations helps a producer make the most informed production decision. Pesticide applications based on economic thresholds optimize grower profits while reducing environmental hazards.
Spray equipment must be properly maintained and calibrated to insure accurate application. Over application results in unnecessary expense to the farmer and increases the risk of environmental contamination, while underapplication could result in poor control. All sprayer components should be clean and in good working order. Measure sprayer output and replace worn nozzle tips, if necessary. Specific guidelines for sprayer calibration are available from your local Cooperative Extension Service office.
Proper handling and disposal of pesticides can reduce the potential for point-source contamination of water resources. Spills or improper disposal of excess spray can overload the soil's ability to hold and degrade pesticides and could result in groundwater contamination. Mix and load pesticides away from the surface water resources or wells. Never dispose of excess pesticide spray by dumping. If possible, apply the excess spray material to a site within label guidelines. After pesticide application is complete, follow label directions for proper container disposal.
Identify areas that are most vulnerable to contamination. Sandy soils or areas with a shallow water table are more vulnerable to groundwater contamination. Similarly, regions with shallow limestone or dolomite deposits may be susceptible to contamination because water can move rapidly through sinkholes. Steep slopes, compacted soils or areas with poor internal drainage are vulnerable to surface runoff.
Conservation tillage practices reduce sediment loading and also reduce or slow water runoff. Since many herbicides can move from treated fields dissolved in runoff water, conservation tillage practices that increase water infiltration into the soil profile can help to reduce herbicide movement into surface water. Herbicides that are moved into the soil, rather than running off, can be degraded by microbial activity, chemical reactions, and plant uptake and metabolism.
Establish grass waterways in areas of concentrated water flow. These waterways will trap sediment and reduce the velocity of runoff flow, allowing greater infiltration of dissolved chemicals. Similarly, grass filter strips have been shown to effectively reduce the amount of herbicide runoff.
Match herbicide application rates to field characteristics and the type of weeds present. Carefully review product labels and follow setback requirements for perennial streams, intermittent streams, and around tile inlets.
Consider split application of soil applied products to reduce the risk of a heavy rainfall event causing extensive runoff. Select postemergence herbicides with physical and chemical characteristics that have less potential for surface runoff. Herbicide combinations and the use of adjuvants with postemergence products may be alternatives to increasing chemical rates. Consider band application of herbicides and use mechanical control when appropriate.
Rotate crops and use a combination of weed management practices. In addition to helping achieve water quality goals, this will reduce the chance for developing herbicide resistant weeds.
Consider delaying pesticide application if heavy rains are forecast for the next few days. Research has shown that heavy rainfall shortly after herbicide application can cause significant chemical loss.
Finally, some individual BMPs may not be appropriate as part of an overall
cropping system. Incorporation of herbicides, for example, has been shown to
decrease the amount of chemical runoff in surface water. Since this practice
is not compatible with a no-till system, the tradeoff between controlling soil
erosion and reducing pesticide movement must be considered.
Individual watershed characteristics can affect the occurrence of herbicides in water supplies. A watershed refers to the land area that drains into a body of water by surface or subsurface flow. The Lake Springfield watershed, for example, includes a 265 square mile area southwest of the actual lake. Since every acre of land is in a watershed, human activities can influence water quality considerable distance away.
Several watershed protection groups have been formed to solve local water quality problems. Farmers and landowners, agricultural chemical dealers, farm mangers, CES, MRCS, Farm Bureau, water utilities and other interested parties help provide different perspectives on the common goal of protecting water resources. Best management practices that are specific to a watershed can be more effectively implemented than treating every acre the same way.
In 1993, the University of Illinois published 50 Ways Farmers Can Protect Their Groundwater. More than 10,000 copies of this reference, which outlined management practices to reduce the risk of groundwater contamination without cutting into yields or profitability, have been sold. A second publication, 55 Ways Farmers Can Protect Surface Water, will be available later this year.
1Extension Educator, Integrated Pest Management, University of Illinois, Springfield Extension Center.
Auerbach, J. 1994. Cost and benefits of current SDWA regulations. Journal AWWA (February) 69-78.
Ciba Crop Protection. 1995. Voluntary atrazine monitoring programs at selected community water systems: Illinois 1994. Technical Report 2-95. Environmental and Public Affairs Department. Greensboro, NC
Goolsby, D. A., R. C. Coupe, and D. J. Markovchick. 1991. Distribution of selected herbicides and nitrate in the Mississippi River and its major tributaries, April through June 1991. U. S. Geological Survey, Water-Resources Investigations Report 91-4163. Denver., CO.
Taylor, A. G. and S. Cook. 1995. Water quality update: The results of pesticide monitoring in Illinois streams and public water supplies. p. 81-84. Proceedings of the Illinois Agricultural Pesticides Conference. University of Illinois at Urbana-Champaign.
Temple D. L. and H. O. Krueger. 1994. An aquatic and sediment monitoring study of cyanazine and selected metabolites in reservoirs in the Midwestern United States. 160 p. Wildlife International Ltd. Easton, MD.
Thurman, E. M., D. A. Goolsby, M. T. Meyer, and D. W. Kolpin. 1991. Herbicides in surface water of the Midwestern United States: The effect of the spring flush. Journal of Environmental Science and Technology:25 (10) 1794-1796.
U.S. Department of Agriculture. 1995. Agricultural fertilizer and chemical usage: Corn - 1994. Illinois Agricultural Statistical Service. Springfield, IL.
Wauchope, R. D. 1978. The pesticide content of surface water draining from agricultural fields - A review. Journal of Environmental Quality 7:459-472.
