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J. R. Plimmer
pesticides such as the organophosphate insecticides are applied to an agricultural
crop, they may be transformed biologically by the action of plant enzymes or
soil microorganisms or they may be transformed chemically by the action of
light, hydrolysis, oxidation, or reaction with soil or biological substrates. In
addition, such physical means as volatilization, adsorption, leaching, and runoff
may dissipate applied pesticides. The relative importance of each process will
be governed by the physical and chemical properties of the pesticide and its
interaction with environmental components.
For a long time, it was assumed that physical, chemical, and biological
reactions occurring in the environment would readily transform residual pesticides into innocuous substances. The past two decades have taught us that this
assumption must be examined very critically, and we now have sufficient experience to realize that the use of pesticides that are resistant to environmental
transformation must be reduced or avoided. As a result, the development of
alternative methods of pest control and the search for biologically active molecules that present fewer residue problems are now recognized as research priorities. Such innovations are accompanied by problems of technology transfer
because a shift in emphasis away from conventional pesticide application techniques, or even the incorporation of new developments into integrated pest
management programs, requires continued acquisition of data and experience
and the development of new pest management skills.
In the case of chemical control of pests that affect stored products, there
are additional special problems. Stored products must be protected from attack
by insects, rodents, and microbial agents; therefore, chemicals used for control
must have a broad spectrum of biocidal activity unless control is to be directed
toward a limited number of species. The chemicals used for this purpose are
usually applied in enclosed situations that afford continued protection against
pests, such as bins, granaries, grain elevators, and holds; thus, the stored product
itself becomes the major recipient of the chemical application, and any chemical
in excess of that used to destroy the target organism is distributed throughout
this commodity. Because the commodity is often intended for human or animal
consumption, it is desirable that as little residual material as possible be retained
and that any such residues be innocuous.
Microbial breakdown, which represents a major pathway for reduction of
pesticide residues in most agricultural applications, is not an available route for
chemicals used for insect control in stored products. Those residual chemicals
that are not volatilized must be degraded by chemical reaction with the substrate,
by hydrolysis, by oxidation, or by photodecomposition (to a limited extent).
Chemicals used for treatment of stored products fall into two major classes:
protectants and fumigants. The former exert residual activity after application
to the substrate or the container; the latter exert their activity in the vapor phase.
J. R. Plimmer
pesticides such as the organophosphate insecticides are applied to an agricultural
crop, they may be transformed biologically by the action of plant enzymes or
soil microorganisms or they may be transformed chemically by the action of
light, hydrolysis, oxidation, or reaction with soil or biological substrates. In
addition, such physical means as volatilization, adsorption, leaching, and runoff
may dissipate applied pesticides. The relative importance of each process will
be governed by the physical and chemical properties of the pesticide and its
interaction with environmental components.
For a long time, it was assumed that physical, chemical, and biological
reactions occurring in the environment would readily transform residual pesticides into innocuous substances. The past two decades have taught us that this
assumption must be examined very critically, and we now have sufficient experience to realize that the use of pesticides that are resistant to environmental
transformation must be reduced or avoided. As a result, the development of
alternative methods of pest control and the search for biologically active molecules that present fewer residue problems are now recognized as research priorities. Such innovations are accompanied by problems of technology transfer
because a shift in emphasis away from conventional pesticide application techniques, or even the incorporation of new developments into integrated pest
management programs, requires continued acquisition of data and experience
and the development of new pest management skills.
In the case of chemical control of pests that affect stored products, there
are additional special problems. Stored products must be protected from attack
by insects, rodents, and microbial agents; therefore, chemicals used for control
must have a broad spectrum of biocidal activity unless control is to be directed
toward a limited number of species. The chemicals used for this purpose are
usually applied in enclosed situations that afford continued protection against
pests, such as bins, granaries, grain elevators, and holds; thus, the stored product
itself becomes the major recipient of the chemical application, and any chemical
in excess of that used to destroy the target organism is distributed throughout
this commodity. Because the commodity is often intended for human or animal
consumption, it is desirable that as little residual material as possible be retained
and that any such residues be innocuous.
Microbial breakdown, which represents a major pathway for reduction of
pesticide residues in most agricultural applications, is not an available route for
chemicals used for insect control in stored products. Those residual chemicals
that are not volatilized must be degraded by chemical reaction with the substrate,
by hydrolysis, by oxidation, or by photodecomposition (to a limited extent).
Chemicals used for treatment of stored products fall into two major classes:
protectants and fumigants. The former exert residual activity after application
to the substrate or the container; the latter exert their activity in the vapor phase.