148
Hugh D. Sisler
Infonnation concerning microbial degradation of benomyl or MBC is very
limited. Helwig (1972) reported degradation of benomyl to nonfungitoxic compounds by bacteria and fungi. Mixed cultures of bacteria were reported to degrade
ring-labeled MBC; 2-aminobenzimidazole (2AB) was identified as one of the
metabolites, and 14C02 was evolved, indicating benzimidazole ring cleavage
(Fuchs and Bollen, 1975). Methyl-5-hydroxy-2-benzimidazole carbamate (5hydroxy-MBC, Fig. 6.12) has been identified as a transfonnation product of
MBC in cultures of the fungi Pellicularia sasaki;, Alternaria mali (Yasuda et
al., 1973), and Aspergillis nidulans (Davidse, 1976). To my knowledge, this
compound has not been reported as a soil metabolite of benomyl, MBC, or
thiophanate-methyl. One avenue of loss of MBC from soil might be the leaching
of this hydroxylated derivative.
Principal residues following benomyl application to plant foliage are benomyl and MBC (Baude et al., 1973). Due to its instability in aqueous solutions
(Clemons and Sisler, 1969), benomyl does not persist for long in plant tissues
(Fuchs et al., 1972; Peterson and Edgington, 1969; Sims et al., 1969). MBC,
on the other hand, is quite stable in plant tissues. Fifty-two days after application
of [l4C]-MBC to roots of pea plants, 78% of the label remaining in the plant
tissue was in MBC (Siegel and Zabbia, 1972). The metabolites present were not
identified except for traces of 2AB. Degradation of MBC was more rapid in
strawberry plants than in pea plants, but except for 2AB the metabolites were
not characterized fully (Siegel, 1973). The benzimidazole nucleus is quite stable
in plants (Siegel, 1973); however, there is evidence for slow degradation. Solei
et al. (1973) reported that about 1.5% of 14C in ring-labeled MBC applied to
melon plants was released as 14C02 in 14 days.
H
H O O N
0
v
"
"
I /.C-NH-C-OCH
~
~
3
N
H
a
N
I )C-NH 2
":::::,..
N
5-Hydroxy-MBC
2-Aminobenzimidazole
Benzimidazole
(X I NH2
~
NH 2
Q - Aminobenzonitrile
Q - Phenylenediami ne
Aniline
Figure 6.12. Degradation products of MBC.
Hugh D. Sisler
Infonnation concerning microbial degradation of benomyl or MBC is very
limited. Helwig (1972) reported degradation of benomyl to nonfungitoxic compounds by bacteria and fungi. Mixed cultures of bacteria were reported to degrade
ring-labeled MBC; 2-aminobenzimidazole (2AB) was identified as one of the
metabolites, and 14C02 was evolved, indicating benzimidazole ring cleavage
(Fuchs and Bollen, 1975). Methyl-5-hydroxy-2-benzimidazole carbamate (5hydroxy-MBC, Fig. 6.12) has been identified as a transfonnation product of
MBC in cultures of the fungi Pellicularia sasaki;, Alternaria mali (Yasuda et
al., 1973), and Aspergillis nidulans (Davidse, 1976). To my knowledge, this
compound has not been reported as a soil metabolite of benomyl, MBC, or
thiophanate-methyl. One avenue of loss of MBC from soil might be the leaching
of this hydroxylated derivative.
Principal residues following benomyl application to plant foliage are benomyl and MBC (Baude et al., 1973). Due to its instability in aqueous solutions
(Clemons and Sisler, 1969), benomyl does not persist for long in plant tissues
(Fuchs et al., 1972; Peterson and Edgington, 1969; Sims et al., 1969). MBC,
on the other hand, is quite stable in plant tissues. Fifty-two days after application
of [l4C]-MBC to roots of pea plants, 78% of the label remaining in the plant
tissue was in MBC (Siegel and Zabbia, 1972). The metabolites present were not
identified except for traces of 2AB. Degradation of MBC was more rapid in
strawberry plants than in pea plants, but except for 2AB the metabolites were
not characterized fully (Siegel, 1973). The benzimidazole nucleus is quite stable
in plants (Siegel, 1973); however, there is evidence for slow degradation. Solei
et al. (1973) reported that about 1.5% of 14C in ring-labeled MBC applied to
melon plants was released as 14C02 in 14 days.
H
H O O N
0
v
"
"
I /.C-NH-C-OCH
~
~
3
N
H
a
N
I )C-NH 2
":::::,..
N
5-Hydroxy-MBC
2-Aminobenzimidazole
Benzimidazole
(X I NH2
~
NH 2
Q - Aminobenzonitrile
Q - Phenylenediami ne
Aniline
Figure 6.12. Degradation products of MBC.