Pirimicarb: The Saga of a Selective Pesticide

The insecticide pirimicarb is a selective aphicide; it controls many of the most damaging aphid pests but has little if any effect on most other arthropods. Because it does not directly interfere with beneficial predatory and parasitic arthropods, it fits well in alternative pest-management programs that rely on biological control. However, pirimicarb had a relatively short early history in the United States; it was first registered in 1974 but was voluntarily withdrawn from the market in 1981 because of regulatory and marketing problems.

Pirimicarb was registered only on specialty crops, specifically potato and greenhouse crops, where aphids are serious pests. After initial registration, the Environmental Protection Agency (EPA) requested additional metabolism and residue information that would have been very expensive to gather. Also during this time, the synthetic pyrethroid insecticides were coming on the market, and many pest managers preferred products such as these that had broad-spectrum activity. Faced with the economics of clearing regulatory hurdles as well as facing competition from the new pyrethroids, it was decided to withdraw registration of pirimicarb in the United States, even though the product continued to be used in Canada and Europe.

Over the past 20 years, the climate in the United States has improved to favor the use of selective products that provide effective and economic alternatives to more broad-spectrum pesticides. Pirimicarb is currently undergoing reregistration review in Europe. Data required for this review will satisfy some of the EPA requirements; therefore the parent company intends to once again submit pirimicarb for registration in the United States.

Had a mechanism been in place in the 1970s to foster the development of specific pesticides by helping companies meet regulatory requirements, pirimicarb and other selective pesticides would likely be more widely used in agriculture today.

SOURCE: Personal communication, 1995, M. Moss, ZENECA Ag Products, Wilmington, Delaware.

crop production in much of the world. In the case of rust diseases, a plant cultivar generally is resistant to only one specific race of a pathogen. Other races of the pathogen can infect the plant, and the shift in race composition of the pathogen leads to a boom-and-bust syndrome of rust diseases. Strategies of resistance-gene deployment, in which fields are planted with mixtures of cultivars, each with a different race-specific resistance gene or with one cultivar containing multiple race-specific resistance genes, can be very successful in diminishing this syndrome. Race-specific resistance genes deployed in this manner can be quite successful in controlling plant diseases. Plants also may have a general resistance to plant pests, conferred by the collective action of multiple genes. Polygenic

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