Over 90 percent of the drinking water consumed in Idaho is supplied by groundwater. This resource is vital to homeowners and industry as well as Idaho's agricultural community. Best management practices (BMPs) for agricultural management have been and are becoming more important.
Groundwater is found in the pores and cracks of underground sand, gravel, and rock deposits. The formation through which it slowly flows is called an aquifer. The top of the water-saturated zone is the water table, and water percolating down to it is called recharge.
Recent surveys by Idaho water quality specialists have found trace amounts of nitrates and, in some cases, pesticides in the drinking water. Nitrates can get into drinking water from many sources, but poor management practices can cause pesticide contamination. Pesticides can get into groundwater through agricultural, industrial, and homeowner uses as well as spills and improper disposal. Contaminated water is difficult and expensive to manage once it becomes dispersed underground.
Careful pesticide application practices will protect the groundwater and help to
ensure personal and public safety. Specific types of BMPs for pesticide
application that should be used in Idaho include:
Some sites are vulnerable to potential contamination, and other sites are tolerant to contamination. You as a potential user of agricultural chemicals have the responsibility of learning the vulnerability of the sites you are going to treat. You need to answer certain questions before you choose to apply chemicals.
Both soil properties and site conditions affect pesticide movement. Soil texture, organic matter content, and permeability are soil factors affecting pesticide movement. Soil conditions that make sites vulnerable to pesticide leaching include:
The physical and chemical properties that make pesticides effective for pest control also create a potential for groundwater contamination. The fate of a pesticide appled to soil depends largely on two of its properties: persistence and adsorption. Persistence is the lasting power of a pesticide. Most pesticides in the soil break down or degrade over time as a result of several chemical and microbiological reactions. Adsorption is the process that binds pesticides to soil particles, like iron filings or paper clips sticking to a magnet. Adsorption occurs because of the attraction between chemicals and soil particles. Factors controlling pesticide adsorption include pesticide charge, soil pH, temperature, water content, and the amount of organic matter present. Pesticide factors that increase the likelihood for pesticide contamination of groundwater include:
Read the Label and Follow Its
The label is a legal document and its instructions should be carefully read. One section will inform you of environmental hazards associated with the pesticide's use. Several common warnings relate to groundwater protection. For example, "(pesticide. . .) can travel (seep or leach) through soil and contaminate groundwater." Other warnings refer to permeable soil types, depth of groundwater, distance to wells, runoff potential, and endangered species. Also be aware of any local restrictions for the pesticides you plan to use.
Mixing and Loading Pesticides
The risks from an accidental spill are higher when mixing and loading concentrated pesticides. Avoid mixing or loading where a spill, leak, or overflow could get into your water source. Load downhill from a well. If necessary, grade the soil or install barriers or a collection pad to divert or contain the flow. Never allow the delivery end of the filler pipe or hose to become submerged as the spray tank is filled. Air space prevents the possibility of back siphoning a pesticide mixture into your water source. Monitor the filling operation and do not allow the tank to overflow.
Calibrate and Avoid Overspray or Drift
Applying too little pesticide may not provide the needed control. Over spraying or exceeding label recommendations not only wastes pesticides but may cause crop damage and leave excessive residues. Errors in either direction can detract from your profits. Excessive amounts of pesticides on the soil surface can move into surface water or groundwater.
Drift from cropland to sensitive sites is always a possibility. The applicator can minimize the risk several ways. Whenever possible, choose pesticides and formulations that are less likely to drift. Consider the use of drift retardant adjuvants. Read the label for any advice it may have on the use of adjuvants. Larger spray droplets have a lower potential for drift. Larger nozzle orifices and lower pressures promote larger droplet sizes. Applications made as close to the target as possible also reduce the possibility for drift. Excessive winds are an obvious cause of drift problems.
Backflow Prevention for Chemigation
Idaho's chemigation law requires antipollution devices to prevent backflow into the water source when adding chemicals through the irrigation system. A chemical injection line check valve is needed. An interlock is needed to shut off the chemical injection when the water supply fails. A sprinkler system (for example) will need an irrigation line check valve, an automatic low pressure drain, and an inspection port. In addition a combination air and vacuum relief valve is required. A gooseneck pipe loop is an alternative. You should read Idaho's chemigation laws and regulations and consult with Idaho Department of Agriculture personnel for possible variances.
Use-up All Diluted Sprays and Properly Dispose of
You need to be sure your sprayer is properly calibrated and you also need to know the exact acreage of the last field you treat with a particular pesticide so that you have no dilute spray material left over after application. This material is a hazardous waste and cannot be disposed of anywhere but a hazardous waste site. The cost of disposal is prohibitive and the wasted pesticide costs money.
Follow Idaho regulations when disposing of pesticides and pesticide containers. Triple rinse or pressure rinse pesticide containers as soon as they are emptied and pour the rinsates into the spray tank. Excess spray mix and rinsates from equipment cleaning can be sprayed on another site or crop listed on the label.
Excess pesticide concentrates must be stored safely until a hazardous waste collection day or disposed of through a hazardous waste transporter, which is very expensive. Triple-rinsed containers are not considered hazardous and may be disposed of at a landfill that will accept them. Unrinsed containers and excess pesticides must be disposed of at a disposal site approved by the Environmental Protection Agency.
Keep Pesticides in a Safe Place Before and After
Pesticides should be kept in cool, dry, and locked storage. The building should be located where there is no danger to wells or groundwater in case of poorly cleaned spills, leaky containers, and heavy rains or flash floods. Containers can be damaged or even lost when transporting them from the field as well as from the warehouse to your storage. After use, return pesticides to storage immediately.
Have a Plan for Pesticide Emergencies
You have probably developed a plan in case someone has been poisoned by a pesticide, but you may not have developed a plan for other pesticide emergencies such as fire, flood, serious spills, or well contamination. You need to notify the fire department of the location of your storage so they will not endanger their lives or flood the pesticides with large volumes of water into vulnerable sites. Have a catch basin around your storage to prevent the pesticides from escaping in case of serious leaks or spills.
Use Non-Chemical Methods of Pest Control When
Sometimes pesticides are not necessary if you properly plan your rotation, use cultural methods of pest control, take advantage of biological control agents, use resistant varieties, alter planting dates, and/or use mechanical methods of pest control. Scout your fields to find if there are economic numbers present to require control measures before treating.
Summary of Best Management Practices for Pesticide
The University of Idaho Cooperative Extension System has over 140 faculty strategically located throughout the state, including 84 agricultural agents and home economists stationed in 42 of 44 counties. In addition, faculty (specialists) are located on campus in Moscow and at research and extension centers in Aberdeen, Caldwell, Idaho Falls, Kimberly, Parma, Sandpoint, Tetonia, and Twin Falls.
This brochure, WQ-14, was prepared by H. W. Homan, R. L. Mahler,
R. W. Clausen, and K. A. Mahler, Entomology and Soil Science Division, University
of Idaho, Moscow, Idaho 83844-2339.
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All contents copyright © 1997-2003. College of Agricultural and Life Sciences, University of Idaho. All rights reserved. Revised: January 3, 2003