Continuing Education and
Communication Services
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
9/10/01
Contacts:
Mark Shour, Extension Entomology, (515) 294-5963, mshour@iastate.edu
Del Marks, Continuing Education and Communication Services, (515) 294-9807,
delmarks@iastate.edu
Yard and Garden Column for the Week Beginning Sept. 14
How Pesticide Bans Affect Homeowner Products
By Mark Shour
Extension Program Specialist
Iowa State University Extension
Aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, kepone, mirex and toxaphene … what do these names have in common? They are insecticides that have been banned from use in the United States.
The first product to be canceled was DDT in 1972. All of these chemicals are fat-soluble, persist in the environment for several years and have chlorine atoms attached to molecules made of carbon and hydrogen (chlorinated hydrocarbons). Most of these insecticides were used on the farm; chlordane and dieldrin were standard control tools for termite and other wood-destroying organisms and DDT had been instrumental against malaria-transmitting mosquitoes. There are three chlorinated hydrocarbon insecticides that are still available for use by homeowners; methoxychlor and dicofol are found in orchard sprays and lindane is used as a borer spray and for head louse control.
Many of the chlorinated hydrocarbons have been implicated in causing various cancers and other human illnesses. Some apparently are responsible for a variety of environmental maladies, including reduced populations of fish-eating birds (eagles, peregrine falcons, brown pelicans) due to eggshell thinning and other reproductive disorders. Water purity analyses from both rural and urban sources still detect some of these chemicals, years after their registrations were revoked.
The scientific community responded by generating volumes of information from the 1960s, addressing the effect of the chlorinated hydrocarbon pesticides on wildlife, domestic animals, the environment and human systems. Some people claimed victory in removing these hazardous insecticides from use, whereas others cried foul for the many alleged "misses" (misinterpretation, misapplication and misrepresentation of scientific data; gross misuse of product; governmental misrule; miscarriage of justice).
There is a second phase of insecticide products that have lost registration or had uses severely restricted by the Environmental Protection Agency (EPA). Some products have been canceled voluntarily by the manufacturer. These activities have occurred primarily from 1990 to the present. Azinphos methyl, chlorpyrifos, diazinon, ethyl parathion and methyl parathion fall into this group. All of these chemicals act by poisoning the nervous systems of animals (neurotoxins) and have oxygen and phosphorus atoms attached to molecules made of carbon and hydrogen (organophosphates).
These insecticides often have important agricultural production uses. Two of these pesticides, chlorpyrifos and diazinon, also have had widespread use in the homeowner market---everything from ready-to-use sprays, to containerized ant or cockroach baits, to granular lawn products, to pet flea collars. Chlorpyrifos (often marketed as Dursban) has been implicated to cause neurophysiological effects, with special concern for nervous system development in children.
Diazinon is the leading cause of acute pesticide poisonings in the United
States. In addition, misapplications on turfgrass have resulted in numerous
bird kills. Chlorpyrifos sales for homeowner uses are to cease by December
2001, whereas diazinon is to be phased out by 2003. The EPA continues
to review pesticides; thus, other products may have use restrictions or
may be banned in the future.
The impact of the loss of chlorpyrifos and diazinon on the Iowa home,
yard and garden remains to be seen. In an informal survey of four garden
centers supplying pesticides to homeowners in central Iowa, chlorpyrifos
was present in 8 to 27 percent of the products, whereas diazinon was present
in 8 to 15 percent of the pesticides sold for use in and around the home.
Many products with active ingredients other than chlorpyrifos and diazinon were present on the garden center shelves. There were four different insecticides labeled for controlling turfgrass pests, 10 products for vegetable garden pests and 16 different active ingredients for use against pests feeding on trees, shrubs, roses and other ornamental plants.
One category of insect pests -- wood and stem borers -- leaves very few effective products for homeowner use. The ban of chlorpyrifos leaves dimethoate, lindane and permethrin as the only products that can be used to protect trees and shrubs from insects that bore into the plants. Because lindane is a chlorinated hydrocarbon and dimethoate is an organophosphate, these products may not be available in the future. Currently, permethrin as a borer preventative is only available to commercial applicators.
Perhaps the banning of chlorpyrifos by EPA should be viewed as a perfect opportunity to shift from reliance on chemicals to integrating control methods. Borers usually colonize plants that have been injured (by lawn mowers or weed trimmers) or are not growing optimally (due to drought, poor soil conditions, improper site, planted too deeply or weather extremes). Proper choice of the plant species for the site and care (watering, light fertilization and keeping it free from other insect pests) maximize the plant growth and enable the plant to defend itself from boring insects. Finally, applying mulch around the base of the tree preserves moisture and eliminates mechanical injury by lawn equipment.
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