Biodegradation of Agricultural Fungicides
135
With regard to toxicity to nontarget organisms other than man, fungicides
such as elemental sulfur, dinocap, and benomyl have deleterious effects on
certain predacious mites and insects and may interfere with the biological control
of some insect pests (Brown, 1978). Frequent application of fungicides of relatively low toxicity can lead to accumulations in soil which affect earthworm
populations. The use of copper fungicides in English orchards over a number
of years has resulted in levels as high as 2000 ppm in the surface layer of soil
and has lead to the disappearance of earthworms (Brown, 1978). Frequent applications of benzimidazole fungicides in orchards results in temporary reduction
of earthworm populations (Stringer and Lyons, 1974). There are, however,
beneficial nontarget effects of fungicides. Benzimidazole fungicides, for example, may aid in the control of parasitic mites (Upham and Delp, 1973) and
nematodes (Miller, 1969).
6.3. STABILITY OF FUNGICIDES
There is considerable literature on this subject, but wide gaps in our knowledge still exist, particularly in respect to the ultimate fate of certain degradation
products. Although stability of organic fungicides or their metabolites is not
Table 6.2. Stability of Various Fungicides in Nonsterile Soil
Half·life
Fungicide
(days)
Comments
Reference
Benomyl
90-365
Based on total
Baude et al.
benzimidazole residues
(1974)
folIowing application of
2.3-5.6 kglha
Captan
3-4
Application rate--l ()() ppm,
Burchfield (1959)
initial soil pH, 6.4
>65
Application rate--I ()()() ppm,
Munnecke (1958)
initial pH 5.7
Chloroneb
30-90
Application rate--2.25 kglha
Rhodes et al.
(1971)
PeNB
117-1059
Based on field samples
Beck and Hansen
(1974)
>21
Flooded (anaerobic soil)
Ko and Farley
(1969)
Thirarn
>40
Not detectable after 40 days
Munnecke and
at application rates of 250
Mickail (1967)
ppm, more persistent at
higher concentrations
Triphenyl tin
140
Based on 1"(:02 released
Barnes et al.
acetate
from 5-10 ppm aromatic(1973)
labeled fungicide
135
With regard to toxicity to nontarget organisms other than man, fungicides
such as elemental sulfur, dinocap, and benomyl have deleterious effects on
certain predacious mites and insects and may interfere with the biological control
of some insect pests (Brown, 1978). Frequent application of fungicides of relatively low toxicity can lead to accumulations in soil which affect earthworm
populations. The use of copper fungicides in English orchards over a number
of years has resulted in levels as high as 2000 ppm in the surface layer of soil
and has lead to the disappearance of earthworms (Brown, 1978). Frequent applications of benzimidazole fungicides in orchards results in temporary reduction
of earthworm populations (Stringer and Lyons, 1974). There are, however,
beneficial nontarget effects of fungicides. Benzimidazole fungicides, for example, may aid in the control of parasitic mites (Upham and Delp, 1973) and
nematodes (Miller, 1969).
6.3. STABILITY OF FUNGICIDES
There is considerable literature on this subject, but wide gaps in our knowledge still exist, particularly in respect to the ultimate fate of certain degradation
products. Although stability of organic fungicides or their metabolites is not
Table 6.2. Stability of Various Fungicides in Nonsterile Soil
Half·life
Fungicide
(days)
Comments
Reference
Benomyl
90-365
Based on total
Baude et al.
benzimidazole residues
(1974)
folIowing application of
2.3-5.6 kglha
Captan
3-4
Application rate--l ()() ppm,
Burchfield (1959)
initial soil pH, 6.4
>65
Application rate--I ()()() ppm,
Munnecke (1958)
initial pH 5.7
Chloroneb
30-90
Application rate--2.25 kglha
Rhodes et al.
(1971)
PeNB
117-1059
Based on field samples
Beck and Hansen
(1974)
>21
Flooded (anaerobic soil)
Ko and Farley
(1969)
Thirarn
>40
Not detectable after 40 days
Munnecke and
at application rates of 250
Mickail (1967)
ppm, more persistent at
higher concentrations
Triphenyl tin
140
Based on 1"(:02 released
Barnes et al.
acetate
from 5-10 ppm aromatic(1973)
labeled fungicide