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Dursban Uses Reduced

June 14, 2000

On June 8, the U.S. Environmental Protection Agency (USEPA) released a revised risk assessment on chlorpyrifos, sold as Dursban, Lorsban, and under other trade names. The main results of this action for ornamental plants is to eliminate the uses by residents and restrict turf use. This is a massive undertaking as there are 147 companies that have 803 labeled products containing chlorpyrifos. Production of residential-size containers of chlorpyrifos, the small containers typically sold to the public in garden centers and hardware stores, will stop by December 1, 2000, with formulators (pesticide producers) stopping sales by February 1, 2001, and retailers will not be able to sell these small containers after December 31, 2001. The only exception is baits in child-resistant packaging.

Homeowners will be able to use chlorpyrifos for as long as they have it. There is no date when home-owners can no longer use the insecticide. By December 1, 2000, remaining chlorpyrifos uses for landscapes and indoors will either be reclassified as restricted-use pesticides or packaged in large containers that are unlikely to be purchased by the general public. There are also restrictions on nonresidential uses. Use in indoor and outdoor areas where children could be exposed, such as schools and parks, will be cancelled according to the same schedule for residential size containers. In addition, in areas where children are not likely to be present, that is, golf courses, road medians, and industrial-plant sites, maximum application rates will be reduced to 1 pound of active ingredient per acre. This 1 pound of active ingredient per acre rate is the same as that currently recommended for all turf insects except for the higher-labeled rates for billbugs, mole crickets, and white grubs. Chlorpyrifos use is not suggested by the University of Illinois on billbugs and white grubs due to control inconsistency.

Use of chlorpyrifos for professional termite control will be phased out by the end of 2005. After December 31, 2000, the rate of application will be below that for which there is reliable data on its effectiveness against termites. Use of chlorpyrifos for mosquito control will continue to be legal but only by professionals.

For all of these uses, there are control options that are at least as effective, except for borer control on trees and shrubs. Lindane is labeled and is effective in most situations as a borer treatment, but it appears likely that lindane will lose its labeling within a few months. Dimethoate, sold as Cygon, is labeled and effective against many borers but is not labeled for many trees and shrubs other than most needled evergreens. Although it appears that professionals can still use chlorpyrifos to control borers in landscapes, the publicity that these restrictions are getting may make it unwise from a customer-relations viewpoint.

These changes are due in part to the Food Quality Protection Act of 1996. Under that law, all uses of a pesticide must fit into a risk cup that covers all exposures by residents and especially children. In addition, repeated research studies have shown that the nervous systems of rat fetuses do not develop properly when exposed to even relatively low levels of chlorpyrifos. These studies showing that chlor-pyrifos crosses the placental barrier cause additional concern about the exposure to children. About 50% of chlorpyrifos is used in and around the home. Cancelling residential use should greatly reduce this level and concurrently reduce exposure. Undoubtedly, recent research that shows that chlorpyrifos is tracked into homes from its presence on turf also added to the concern. There apparently is no other new research on toxicity that is driving these decisions.

In summary, all residential uses end in about 18 months, except for bait stations. All emulsifiable concentrates will become restricted-use pesticides, and all other formulations will be packaged in large quantities that are unlikely to be used by homeowners. Additional information can be obtained at USEPA’s Web site: http://www.epa. Gov/pesticides/op/ chlorpyrifos.htm.

Author: Phil Nixon


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