A well-maintained, healthy lawn and lush ornamentals increase property values, help prevent erosion, conserve water, deaden sound, supply oxygen, and increase aesthetic and recreational values.  But landscaping requires intensive care, such as watering, fertilizing, mowing, and pest control.  Protecting the environment also requires care because some pesticides, specifically insecticides, herbicides, and fungicides, may be washed from lawn areas to surface and ground waters.

Public concern generally focuses on the use of pesticides and fertilizers on large tracts of agricultural land.  But, for the urban and suburban environment, residential use may be a greater concern.  Pesticides, fertilizers, and other active materials are used extensively in the urban, suburban, and residential environment.  Studies have shown that, after a heavy summer rain, nitrates and pesticides increase dramatically in streams and lakes near areas of urban or suburban development.

Use of pesticides and fertilizers in residential areas is very different from agricultural uses.  In residential areas, chemicals are applied to smaller areas, but applications may be heavier and more frequent.  Some lawns, for example,  receive 10 or more pesticide applications per season, and two or three times as much nitrogen as a typical field crop.

Pesticide Movement

Pesticides are designed to stay in place to control the target pest, then degrade into harmless products. However, some pesticides can move from the site of application to the surrounding area.  Pesticides leave the target area by degradation or breakdown, evaporation to the atmosphere, leaching to ground water, and runoff to surface water.

Runoff is the most direct route to surface ponds, lakes, or streams.  Even if no body of water is visible, runoff may reach a water body by way of ditches, storm sewers, or underground drainage pipes.  This is a concern particularly in subdivisions where numerous manicured lawns are treated with pesticides and fertilizers.  Runoff from such areas can upset nearby ecosystems and threaten wildlife.  Pesticides differ in their relative runoff potential, as shown in the following tables.

Leaching is the extraction of chemicals from soil by water moving through the soil.  Most pesticide chemicals degrade rapidly in soil.  But, if they are highly leachable, they may reach ground water before they are degraded. In rainy periods or when there is excessive irrigation, leachable chemicals are likely to move to ground water. The tables show the relative leaching potential of commonly used chemicals.

Degradation is the time it takes a pesticide to degrade (break down into simpler substances).  Degradation rate is measured by half-life—the time it takes for half of the active ingredient to break down.  For example, half-life of the insecticide Sevin is 10 days.  Therefore, one ounce of active ingredient would degrade to a half ounce in 10 days.  In another 10 days, only one-fourth ounce (half of a half ounce) would remain, and so on.  Materials with a shorter half-life are less persistent than those with a longer half-life.  Tables 1 through 3 show the degradation rate, expressed as half-life in soil, for some commonly used pesticides.

Evaporation (or volatilization) is the loss of pesticide to the atmosphere.  In most cases, this is not a big concern for water quality, although some evaporated pesticide may return to earth on dust particles or in rainfall.  Evaporation can also contribute to air pollution.  Perhaps the biggest concern is that evaporative loss reduces the effectiveness of the pesticide, requiring extra pesticide treatments with more handling, rinsings, and disposal problems.

Recommendations

1. Always read the label before purchasing a pesticide.  Read it again before applying.
2. Do not apply pesticides when rain is imminent.  Pesticides need time to dry and work.
3. Do not spray pesticides when it is windy.
4. Note the temperature range specified on the label.  High temperature may increase evaporative loss or cause plant injury.
5. Use the correct amount of water.  If too much water is used, the pesticide may not work properly and may be more likely to run off.
6. Calibrate your sprayer.  Too little won't work.  Too much may damage the environment.
7. Use Integrated Pest Management (IPM) to control pests.
8. To protect ground water, select pesticides with low leaching potential.
9. To protect streams and lakes, consider runoff potential.
10. Where possible, substitute low-toxicity, short-lived chemicals for high-toxicity and long-lived chemicals.
11. Finally, use care when handling chemicals and disposing of the leftover material.

Integrated Pest Management for Residential Areas

Integrated Pest Management (IPM) uses biological principles, cultural practices, and some chemicals to control pest populations with minimal environmental impact.

• Select adapted plant materials, considering resistance to commonly occurring pests.
• Select high-quality seed or sod, free of weeds, insects, and disease.
• Use proper planting and establishment techniques to minimize perennial weeds and other problems.
• Manage fertility with soil tests to maintain vigorous growth without excess fertilizer.
• Identify status and abundance of pests.
• Adjust cultural practices, such as mowing, fertilization, irrigation, aerification, and dethatching.  Use mechanical alternatives, such as hand pulling or cultivation, instead of a pesticide.
• Use spot treatments instead of broadcast application.

Impact of Pesticides on Aquatic Organisms

Pesticides in the environment are generally a concern because they kill organisms other than the target insect, weed, or disease organism.  Toxicity varies by species and may be either acute or chronic.  Acute toxicity is fast-acting, affecting organisms directly.  Chronic toxicity is more subtle.  It results from low-level, frequent exposure, and its effects may not be recognized until much later.

Acute toxicity is measured by testing the chemical on a population of organisms, such as invertebrates, fish, or birds.  Toxicity is reported as the median lethal dose (LD₅₀) or the median lethal concentration (LC₅₀).  LD₅₀ is the dose (mg of chemical/kg of body weight) that will kill 50 percent of the designated organisms in a specified period of time, usually 24 to 96 hours.  The lower the LD₅₀ or LC₅₀, the more dangerous the chemical.  Toxicity of some commonly used pesticides to mallard ducks, fish, and aquatic invertebrates is shown in the tables.

Bioaccumulation

Bioaccumulation is the concentrating effect that occurs when many microscopic organisms, contaminated by pesticides, are eaten by organisms higher in the food chain. For example, DDT sprayed on insects accumulated in small mammals, birds, and people. The concentration of pesticides in the tissue of organisms at the top of the food chain may be far greater than the concentration in the water or surrounding environment. Accumulated pesticide may kill the higher organism, or it may have more subtle effects, such as reducing the organisms reproductive capabilities. Today's pesticides do not bioaccumulate.

Reducing Environmental Impact

Pesticide formulation, application timing, and application method can affect runoff and leaching. For example, if it rains, wettable powder formulations are much more likely to be washed off a surface than are emulsified concentrate formulations.3 Timing is important because effectiveness varies with growth stage and pest population. Spraying for a pest that is not present can waste chemicals and threaten the environment. Likewise, some application methods, such as spot treatment, may be better than broadcast spay.

Pesticide selection can be adjusted to avoid known problems.  For example, if soils are sandy or ground water is near the surface, a pesticide with low leaching potential is desirable.  If a pond with fish or ducks is nearby, the chemical's runoff potential and its specific toxicity should be considered.

Care in application and disposal.  Improper handling of chemicals, indiscriminant spraying, and dumping are serious concerns.  Do not apply more pesticide than allowed by the product's label, and never pour pesticide in a storm sewer or other channel.

Water management.  Over-watering lawns can leach pesticides below the reach of plant roots.  This increases the chance of contaminating ground water, particularly if the chemical has high leaching potential.

Identify your pests and use Integrated Pest Management (IPM) [see box on page 2].  Exploring the options for pest control may require expert advice, as well as personal research.  For information about pest identification and IPM, visit your County Extension Office.

Table 1. Characteristics of commonly used insecticides.

^aToxicity to mallard ducks^1,4,7,9 is based on LD₅₀

very low = more than 2,000mg/kg

low = >500 to 2,000

medium = >50 to 500

high = 10 to 50

very high = less than 10mg/kg

^bToxicity to fish^4,6,8 and aquatic invertebrates^1,8 is based on 48- or 96-hour LC₅₀

very low = more than 100mg/l

low = >10 to 100

medium = >1 to 10

high = 0.1 to 1

very high = less than 0.1mg/l
^cFish toxicity based on catfish and bluegill
^dCatfish are less sensitive
^eBluegill are less sensitive

Table 2. Characteristics of commonly used herbicides.

^aToxicity to mallard ducks^1,4,7,9 is based on LD₅₀

very low = more than 2,000mg/kg

low = >500 to 2,000

medium = >50 to 500

high = 10 to 50

very high = less than 10mg/kg

very low = more than 100mg/l

low = >10 to 100

medium = >1 to 10

high = 0.1 to 1

very high = less than 0.1mg/l

^cFish toxicity based on catfish and bluegill
^d2,4-D butoxyethanol ester has medium to high toxicity to fish

Table 3. Characteristics of commonly used fungicides.

^aToxicity to mallard ducks^1,4,7,9 is based on LD₅₀

very low = more than 2,000mg/kg

low = >500 to 2,000

medium = >50 to 500

high = 10 to 50

very high = less than 10mg/kg

^bToxicity to fish^4,6,8 and aquatic invertebrates^1,8 is based on 48- or 96-hour LC50

very low = more than 100mg/l

low = >10 to 100

medium = >1 to 10

high = 0.1 to 1

very high = less than 0.1mg/l
^cFish toxicity based on catfish and bluegill
^dBluegill are less sensitive

References

1. Extoxnet, 1989.  "Pyrethrins and Pyrethroids."  Michigan State University.
2. Terrell, C. R., and P. B. Perfetti.  1989.  Water Quality Indicators Guide:  Surface Waters, U. S. Dept. of Agriculture, Soil Cons. Serv. SCS-TP-161.
3. Water Quality Reference Handbook.  1988.  USDA-SCS.
4. Hartley, D., and H. Kidd, (Eds.). 1983.  The Agrochemicals Handbook, 2nd ed.  The Royal Society of Chemistry, The University Nottingham, England.
5. "Avian Single-Dose Oral LD50."  1985.  Hazard Evaluation Division Standard Evaluation Procedure.  Environmental Protection Agency, Washington D.C.
6. Toth, S. J., G. L. Jensen, and M. L. Grodner.  "Acute Toxicity of Agricultural Chemicals to Commercially Important Aquatic Organisms."  Louisiana Coop. Ext. Serv. Publ. 2343.
7. Smith, G.  1970.  Pesticide use and toxicity in relation to wildlife—organophosphorus and carbamate compounds.  U.S. Dept. of Fish and Wildlife Serv. Res. Publ.  Washington D.C.
8. Johnson, W. W. , and M. T. Finely.  1980.  Handbook of acute toxicity of chemical to fish and aquatic invertebrates.  U.S. Dept. of Int., Fish and Wildlife Serv. Res. Publ.  137. Washington D.C.
9. Hudson, R. H., R. K. Tucker, and M. A. Haegele.  1984.  Handbook of Toxicity of Pesticides to Wildlife, 2nd ed.  U.S. Dept. of Int., Fish and Wildlife Serv. Res. Publ. 153.  Washington D.C.
10. Hornsby, A., and Audustgin (Eds.).  1991.  Pesticide Parameter Database.  In:  Handbook on Managing Pesticides for Crop Production and Water Quality Protection.  SS-SOS-3.

Brad Kard
Professor, Structural and Urban Entomology

Kevin Shelton
Extension Pesticide Coordinator

Charles Luper
Extension Associate