- Operations and Timing
- Application Practices
- Potential Environmental Problems
- Best Management Practices
Pesticides are used to control pests, which include insects, mice and other animals, unwanted plants (weeds), fungi, or microorganisms like bacteria and viruses. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides (that control weeds), fungicides (that control fungi), and substances used to control other pests.
Pesticides are used on the vast majority of U.S. cropland. According
to agricultural chemical usage statistics from USDA, herbicides were applied
to 98% of corn acreage and 96% of soybean acreage in 2001.
Operations and Timing
The label includes information on when the product should be applied. Labels often list the minimum number of days which must pass between the last pesticide application and harvest of crops or grazing by livestock. These are intervals set by EPA to allow time for the pesticide to break down in the environment, preventing residues on food, feed, or animal products.
More and more producers have their pesticides applied by commercial applicators. This practice has many advantages, such as not having to store pesticides on-farm, avoiding having to be certified as pest control applicators, and benefiting from the dealer's record keeping.
- Aerial Application
Aerial application of pesticides has several advantages for the modern agricultural producer. When properly managed, aerial application offers speed of dispersal, accessibility to crops on areas where ground equipment cannot operate, and reasonable cost. In many cases, aerial application also allows more timely applications and, therefore, better utilization of pesticides.
Aerial application programs require good cooperation between the pilot and grower. It must also recognize the potential dangers to people, other crops and the environment.
Limitations on aerial application include weather hazards, fixed obstacles such as radius towers, field size and shape, the distance from the point of application to the landing area, and the danger of contamination of nearby areas due to drift or misapplication. Careless applications can be harmful to the crop, the grower and the applicator.
A growing practice in many areas of the country is the application of pesticides through irrigation systems, often termed "chemigation." Although there are systems specifically designed for chemigation, in most cases an existing irrigation system is modified to mix the chemical with irrigation water. Fertilizers are generally stored in large tanks located near wells drawing ground water for irrigation. Fertilizers flow from the storage tanks into the irrigation water. Concerns about groundwater contamination from this practice arise from the fact that accidental backflow or siphoning of chemicals into the well can occur when the irrigation pumping system shuts down unexpectedly.
Potential Environmental Concerns
The likelihood of pesticide contamination of groundwater and water wells depends partly on the geologic and hydrologic characteristics that vary from location to location as well as on pesticide characteristics.
Contamination of drinking water wells by pesticides is usually the result of one or more of the following:
- Improper application of pesticides on the fields
- Careless handling of the pesticides
- Careless storage of pesticides
- Careless disposal of unused pesticides and pesticide containers.
Ideally, pesticides should be applied at just the right time to control pests, then degrade into harmless compounds in the soil, air, or water without contaminating the environment. However, this is difficult to attain. Pesticides have the potential to harm the environment by injuring nontarget plants and animals, leaving harmful residues, or moving from the application site into the surrounding environment.
Some pesticides (called accumulative pesticides) can build up in the bodies of animals over time, including humans. These persistent pesticides stay in the environment without change for long periods of time. Pesticides which break down quickly in the environment to form harmless materials area called non-persistent. Most agricultural pesticides used in the U.S. are broken down easily by microorganisms or sunlight.
Pesticides come into contact with nontarget insects and plants through drift, runoff, or spills. Drift to nearby areas may injure fish, birds, other wildlife, and sensitive plants. It can also damage nearby crops, forests, or landscape plantings. Poorly timed applications can kill bees and other pollinators which are working in the area, or beneficial parasites and predators that help control pests naturally .
Pesticides have the potential to contaminate both surface waters (lakes, streams, ponds, rivers) and ground water.
Pesticides can move into surface water through surface runoff, attached to eroding soil particles, or from tile drainage systems. Concerns about pesticide movement in surface runoff include pesticide persistence, time between application and a runoff event, and any management practices in place that reduce surface runoff from the field.
Pesticides can also leach into ground water. The soil type plays an important role in determining the extent to which pesticides leach to ground water. Sandy soils greatly increase the risk of pesticide loss, because they have very limited capacities to adsorb pesticides. In karst areas, pesticides can easily reach ground water through sinkholes. Pesticides may also enter ground water via improperly constructed wells or by back-siphoning into wells while mixing and filling the applicator chemicals. Cases of ground water contamination have also been traced to spills and improper handling of pesticides (such as improper disposal of excess spray and rinsate from cleaning equipment).
The EPA has labeled some commonly used pesticides as having a high probability of moving into ground water when applied to very porous soils. Some pesticides are required to have a statement on their label such as "This product is a chemical that can travel through the soil and contaminate ground water, which may be used as drinking water. This product has been found in ground water because of agricultural use. Users are advised not to apply this product where the water table is close to the surface or where soils are very permeable. Your local Cooperative Extension Service Office can provide further information on the type of soil in your area and the location of ground water".
Best Management Practices
- Integrated pest management (IPM): IPM programs use a range of methods and disciplines to assure stable and economical crop production while minimizing risks to humans, animals, plants and the environment. IPM weighs costs, benefits, and impacts on health and the environment and thus identifies the most suitable ways to control pests. Options include prevention, monitoring, mechanical trapping devices, natural predators, biological pesticides, and, if appropriate, chemical pesticides.
- Pesticide selection: Select a pesticide that will have the least impact on the environment. Environmental impacts of pesticides depend on sorption (how tightly pesticide is held by the soil surfaces), water solubility (the amount of pesticide that will dissolve in a given amount of water), and persistence (the amount of time a pesticide remains in the environment. Pesticides with high sorption and low solubility are much less likely to leach into groundwater, or be transported by runoff. Pesticides with low persistence (short half-life) are likely to break down into less harmful compounds before they have a chance to harm the environment.
- Timing: Apply pesticides only when they are needed for pest control, and when conditions are least likely for the pesticide to move to ground or surface water. Contamination events often happen when pesticides are applied just before a high-intensity rainfall, when runoff can move the newly-applied pesticide into lakes and streams. The window of highest vulnerability for pesticide runoff is typically within 10 to 15 days after application.
- Sprayer calibration: Apply the correct amount,
which can only be done if sprayers are calibrated regularly.
Spray nozzles are an important part of pesticide application equipment. Quality nozzles can reduce pesticide use and reduce environmental pollution.
In row crops, nozzle patterns are directed downward. In citrus and other tree crop applications, it is a common practice to direct half the spray volume laterally toward the upper half of the tree and the rest to the lower half.
Sprayer calibration: Application errors can originate from either incorrect pesticide concentration in the tank, (mixing error) or incorrect sprayer output per unit area (calibration error). The latter may be due to travel speed, nozzle pressure, or the use of improper, defective and worn nozzles. By properly matching sprayer discharge rate, swath width and travel speed, calibration errors can be minimized. Sprayer calibration can be carried out by:
a) determining the amount of the tank mix used to spray a known area;
b) operating the sprayer in a fixed place and measuring the amount of discharged liquid (water) for a specified time;
or c) collecting the nozzle discharge and determining the output for a time period.
The use of high capacity nozzles at low pressures to achieve low-volume application rates, one-sided calibration of the sprayer for two-sided operations and vice versa, calibration at closed pressure settings and intermittent operation of the nozzles can introduce errors in application rates. Sprayers using positive displacement pumps (diaphragm, piston, etc.) have more potential for application error compared to sprayers using centrifugal pumps, particularly at high volume rates.
Source: Florida Cooperative Extension Service/Institute of Food and Agricultural Sciences/University of Florida
- Consider alternatives: Alternatives to chemical
- Biological pesticides, which target specific pests. Because of this targeting, these methods are generally considered to pose less risk to human beings, other species and the environment.
- Microbial pesticides, which are naturally occurring or genetically altered microorganisms including fungi, viruses, and bacteria.
- Pheromones, which disrupt normal mating behavior by stimulating breeding pests and luring them into traps.
- Cultural practices such as different tillage practices and not growing the same crop every year (crop rotation)
- Avoid sensitive areas: Know the location of sensitive areas such as sinkholes, depressions, wells, surface water, public institutions. For example, buffer zone should be in effect when applying pesticides around these sites. A buffer is required between the application of atrazine, one of the most common herbicides, and wells or surface water.