Application of Biodegradable Pesticides in India
271
used most often, and proper dosages have been worked out (Agnihothrudu and
Mithyantha, 1978).
10.5. FARM MANAGEMENT AND METABOLISM
10.5. 1. Organophosphorus Compounds
A majority of the organophosphorus insecticides in use are basically of a
single chemical nature and are the derivatives of phosphoric acid. They also
have a uniform mode of action. Organophosphorus compounds have the characteristic feature of persistence only for short periods of time.
Organophosphorus insecticides have a brief half-life ranging from 1 to 3
weeks. Phosphamidon, for example, has a half-life of 1-3 weeks in soil and
water. Phosphamidon leaches out from many soils, and as such it does not
accumulate in the top layer of soil. Samples of air taken in orchards 1-24 hr
after spraying show less than 0.01 mg of phosphamidOnlm2 (Voss and GeissbUhler, 1971).
The rates of degradation of phosphamidon, diethylphosphamidon and
gamma chlorophosphamidon have been assessed under laboratory and greenhouse conditions. These compounds are degraded rapidly in green leaves. Fruits
degraded them at a much lower rate. Phosphamidon is degraded in sea water,
its half-life in sea water being approximately 2 weeks. The rate of degradation
in soil depends upon the type of soil and the initial residue level.
Dicrotophos persisted in soil up to 75 days. Degradation slowed down in
the presence of fertilizers (Pandey and Agnihotri, 1975). While diazinon was
found in harvested paddy plants even 50 days after application, no residues could
be detected in soil (Gupta, 1974). There was quick degradation of chlorfenvinphos in soil, and no residue was found in the potato plant and its tubers (Misra
et al., 1977). Disulfoton degraded in soil 30 days after application (Rajukkannu
et al., 1973). There is, however, a need to estimate the level of pesticide residues
in potatoes (Solanum tuberosam) and onions (Allium cepa), which are kept in
cold storage and released periodically into the market. Phorate and disulfoton
dissipated quickly from the rape seed (Jain et al., 1974). Dimethoate (0.03%
spray) degraded quickly, and no residue was seen after 48 hr of treatment of
tobacco plants (Joshi and Ramaprasad, 1969). Dimethoate was not found on
peach and guava (Psidium guajava). Approximately 50% of the initial deposit
was degraded within 3-5 days. Grapes treated with fenthion four times at 15day intervals showed very low residues (Rajukkannu et al., 1977a). Rapid degradation, however, was noticed, and in 8 days no residue could be detected.
Persistence of malathion residues in the cow pea (Vigna sinensis) has been
271
used most often, and proper dosages have been worked out (Agnihothrudu and
Mithyantha, 1978).
10.5. FARM MANAGEMENT AND METABOLISM
10.5. 1. Organophosphorus Compounds
A majority of the organophosphorus insecticides in use are basically of a
single chemical nature and are the derivatives of phosphoric acid. They also
have a uniform mode of action. Organophosphorus compounds have the characteristic feature of persistence only for short periods of time.
Organophosphorus insecticides have a brief half-life ranging from 1 to 3
weeks. Phosphamidon, for example, has a half-life of 1-3 weeks in soil and
water. Phosphamidon leaches out from many soils, and as such it does not
accumulate in the top layer of soil. Samples of air taken in orchards 1-24 hr
after spraying show less than 0.01 mg of phosphamidOnlm2 (Voss and GeissbUhler, 1971).
The rates of degradation of phosphamidon, diethylphosphamidon and
gamma chlorophosphamidon have been assessed under laboratory and greenhouse conditions. These compounds are degraded rapidly in green leaves. Fruits
degraded them at a much lower rate. Phosphamidon is degraded in sea water,
its half-life in sea water being approximately 2 weeks. The rate of degradation
in soil depends upon the type of soil and the initial residue level.
Dicrotophos persisted in soil up to 75 days. Degradation slowed down in
the presence of fertilizers (Pandey and Agnihotri, 1975). While diazinon was
found in harvested paddy plants even 50 days after application, no residues could
be detected in soil (Gupta, 1974). There was quick degradation of chlorfenvinphos in soil, and no residue was found in the potato plant and its tubers (Misra
et al., 1977). Disulfoton degraded in soil 30 days after application (Rajukkannu
et al., 1973). There is, however, a need to estimate the level of pesticide residues
in potatoes (Solanum tuberosam) and onions (Allium cepa), which are kept in
cold storage and released periodically into the market. Phorate and disulfoton
dissipated quickly from the rape seed (Jain et al., 1974). Dimethoate (0.03%
spray) degraded quickly, and no residue was seen after 48 hr of treatment of
tobacco plants (Joshi and Ramaprasad, 1969). Dimethoate was not found on
peach and guava (Psidium guajava). Approximately 50% of the initial deposit
was degraded within 3-5 days. Grapes treated with fenthion four times at 15day intervals showed very low residues (Rajukkannu et al., 1977a). Rapid degradation, however, was noticed, and in 8 days no residue could be detected.
Persistence of malathion residues in the cow pea (Vigna sinensis) has been