FUNGICIDES Fungicides used in agriculture to control plant diseases belong to various chemical
1.4 FUNGICIDES Fungicides used in agriculture to control plant diseases belong to various chemical
classes. A wide variation of physicochemical properties of these substances can be observed, according to the different chemical structures of fungicides. Some fungi- cides are stereoisomers and they are normally commercialized as mixtures of these isomers. Fungicides can be applied pre- or postharvest for the protection of cereals, fruits, and vegetables from fungal diseases.
1.4.1 A ZOLES
N Cyproconazole
The imidazole ring is present in several biologically active compounds, while others have a triazole ring. These compounds are fungicides with systemic action, effective against several phytopathogenous fungi and recommended for seed dressing, as well as foliage fungicide and postharvest application in fruits. They are scarcely soluble in water, although their salts are soluble in water (Table 1.18).
1.4.2 B ENZIMIDAZOLES
HN
Thiabendazole
Fungicides of the benzimidazole type have a systemic action. Generally, they are taken up by the roots of the plants, and the active substances are then acropetally translocated through the xylem to the leaves. These compounds have been used in plant protection in the form of their insoluble salts. They are foliage and soil
24 TABLE 1.17 Chemical Names and Properties of Pyrethroid Insecticides
Water Solubility Half-Life in Common Name
Vapor Pressure
K ow
mg=L (258C) Soil (Days) Acrinathrin
IUPAC Name
mPa (208C)
log P
(S)-a-Cyano-3-phenoxybenzyl (Z)-(1R,3S)-2,2-dimethyl- 4.4 3 10 5 5.6 5 –100 C 26 H 21 F 6 NO 5 3-[2-(2,2,2-trifluoro-1-trifluoromethyl ethoxycarbonyl)vinyl] cyclopropanecarboxylate
Analysis Cyfluthrin
(RS)-a-Cyano-4-fluoro-3-phenoxybenzyl(1RS,3RS;
56 C 22 H 18 Cl 2 FNO 3 1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethyl
I: 2.2 3 10 3a –63 cyclopropanecarboxylate
IV: 2.9 3 10 3 Pesticides Cypermethrin
IV: 8.5 3 10 5 IV:5.9
60 C 22 H 19 Cl 2 NO 3 3-(2,2-dichlorovinyl)-2,2-dimethyl cyclopropanecarboxylate Deltamethrin
(RS)-a -Cyano-3-phenoxybenzyl(1RS,3RS; 1RS,3SR)-
(S)-a-Cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dibromovinyl)- 1.24 3 10 5b 4.6 <0.2 3 10 3 23 in C 22 H 19 Br 2 NO 3 2,2-dimethyl cyclopropanecarboxylate
Food Esfenvalerate
35 –88 C 25 H 22 ClNO 3 3-methylbutyrate Tau-fluvalinate
(S)-a-Cyano-3-phenoxybenzyl-(S)-2-(4-chlorophenyl)-
2 3 10 4b 6.22 0.002
(RS)-a-Cyano-3-phenoxybenzyl-N-(2-chloro- 9 3 10 8 4.26 0.001 a 12 –92 and
Environmental Permethrin
C 26 H 22 ClF 3 N 2 O 3 a ,a,a-trifluoro-p-tolyl)- D -valinate
3-Phenoxybenzyl-(1RS,3RS;1RS,3SR)-
6.1 a 6 3 10 3a <38 C 21 H 20 Cl 2 O 3 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate
cis : 0.0025
trans : 0.0015
Sources: Data from Tomlin, C. (Ed.) in The Pesticide Manual, British Crop Protection Council, 2000; http:==ec.europa.eu=food=plant=protection=evaluation=exist _subs_rep_en.htm; http:==www.epa.gov=opprd001=factsheets=; Hornsby, A.G., Wauchope, R.D., and Herner, A.E. in Pesticide Properties in the Environment, Springer-Verlag, New York, 1996; De Liñan, C. in Farmacología Vegetal, Ediciones Agrotecnicas S.L., 1997.
Samples a 208C. b 258C.
Pesticides:
TABLE 1.18 Chemical Names and Properties of Azole Fungicides
Classi
Water Solubility Half-Life in Common Name
Vapor Pressure
K ow
mg=L (208C) Soil (Days) fi cation Cyproconazole
IUPAC Name
mPa (208C)
log P
(2RS,3RS;2RS,3SR)-2-(4-Chlorophenyl)-3-cyclopropyl-1-(1H-1,2,4-triazol-1-yl) 0.04 2.91 140 a 90 C 15 H 18 ClN 3 O
butan-2-ol and Flusilazole
Bis(4-fluorophenyl)(methyl)(1H-1,2,4-triazol-1-ylmethyl)silane 0.04 a 3.74 54 95 C 16 H 15 F 2 N 3 Si
Properties Hexaconazole
3.9 17 — C 14 H 17 Cl 2 N 3 O Imazalil
(RS)-2-(2,4-Dichlorophenyl)-1-(1H-1,2,4-triazol-1-yl)hexan-2-ol
3.82 180 150 C 14 H 14 Cl 2 N 2 O Prochloraz
N -Propyl-N-[2-(2,4,6-trichlorophenoxy)ethyl]imidazole-1-carboxamide 0.09 4.12 34.4 a 120 C 15 H 16 Cl 3 N 3 O 2 Propiconazole
0.03 3.72 100 110 C 15 H 17 Cl 2 N 3 O 2 Tebuconazole
3.7 36 — C 16 H 22 ClN 3 O Triadimefon
(RS)-1-p-Chlorophenyl-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)pentan-3-ol
(1-(4-Chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)butan-2-one 0.02 3.11 64 6 –60 C 14 H 16 ClN 3 O 2
Sources: Data from Tomlin, C. (Ed.) in The Pesticide Manual, British Crop Protection Council, 2000; http:==ec.europa.eu=food=plant=protection=evaluation=exist _subs_rep_en.htm; http:==www.epa.gov=opprd001=factsheets=; Hornsby, A.G., Wauchope, R.D., and Herner, A.E. in Pesticide Properties in the Environment, Springer-Verlag, New York, 1996; De Liñan, C. in Farmacología Vegetal, Ediciones Agrotecnicas S.L., 1997.
a 258C. 25
26 Analysis of Pesticides in Food and Environmental Samples
TABLE 1.19 Chemical Names and Properties of Benzimidazole Fungicides
Water Half-Life Common
Vapor
K ow Solubility in Soil Name
IUPAC
Pressure
log P mg=L (258C) (Days) Benomyl
Name
mPa (258C)
1.37 0.003 67 C 14 H 18 N 4 O 3 benzimidazol-2-ylcarbamate Carbendazim
Methyl 1-(butyl carbamoyl)
Methyl benzimidazol- 0.15 1.51 8 120 C 9 H 9 N 3 O 2 2-yl carbamate Thiabendazole
2-(Thiazol-4-yl)benzimidazole 4.6 3 10 4 2.39 30 a 33 –120 C 10 H 7 N 3 S
Sources: Data from Tomlin, C. (Ed.) in The Pesticide Manual, British Crop Protection Council, 2000; http:==ec.europa.eu=food=plant=protection=evaluation=exist_subs_rep_en.htm; http:==www.epa .gov=opprd001=factsheets=; Hornsby, A.G., Wauchope, R.D., and Herner, A.E. in Pesticide Properties in the Environment , Springer-Verlag, New York, 1996; De Liñan, C. in Farmacología Vegetal , Ediciones Agrotecnicas S.L., 1997.
a 208C.
fungicides with a specific and broad spectrum of action, also used for seed treatment and in postharvest (Table 1.19).
1.4.3 D ITHIOCARBAMATES Ethylenebisdithiocarbamates are prepared from ethylene diamine H 2 N –CH 2 –
CH 2 –NH 2 . [SC(S)NHCH 2 CH 2 NHCSSMn] x Zn y
Mancozeb
These compounds are heavy metal salts of ethylenebisdithiocarbamate and these salts are unusually stable and suitable as fungicides. The dithiocarbamate fungicides are the most widely used organic fungicides and have a wide spectrum of activity as foliar sprays for fruits, vegetables, and ornamentals and as seed protectants (Table 1.20).
1.4.4 M ORPHOLINES
CH 3
CH 3
(H 3 C) 3 C CH 2 CHCH 2 N
CH 3
Fenpropimorph
Morpholines are specific systemic fungicides against powdery mildew fungi and are used to control the disease in cereals, cucumbers, apples, and so on. These
Pesticides: Classification and Properties 27
TABLE 1.20 Chemical Names and Properties of Dithiocarbamate Fungicides
Vapor
Water
Solubility Half-Life Common
Pressure
K ow mg=L in Soil Name
IUPAC
mPa
log P (258C) (Days) Mancozeb
Name
(208C)
1.8 6.2 6 –15 (C 4 H 6 MnN 2 S 4 ) x (Zn) y
Manganese ethylenebis
(dithiocarbamate) (polymeric) complex with zinc salt
Maneb Manganese
0.45 257 25 C 4 H 6 MnN 2 S 4 ethylenebis (dithiocarbamate)
Metiram Zinc ammoniate
0.3 0.1 20 (C 16 H 33 N 11 S 16 Zn 3 ) x
ethylenebis (dithiocarbamate)- poly(ethylenethiuram disulfide)
Nabam Disodium ethylenebis
Negligible
C 4 H 6 N 2 Na 2 S 4 (dithiocarbamate) Zineb
10 23 (C 4 H 6 N 2 S 4 Zn) x
Zinc ethylenebis
(dithiocarbamate) (polymeric)
Ziram Zinc bis
1.23 1.58 –18.3 a 2 C 6 H 12 N 2 S 4 Zn
(dimethyldithiocarbamate) Sources: Data from Tomlin, C. (Ed.) in The Pesticide Manual, British Crop Protection Council, 2000;
http:==ec.europa.eu=food=plant=protection=evaluation=exist_subs_rep_en.htm; http:==www.epa .gov=opprd001=factsheets=; Hornsby, A.G., Wauchope, R.D., and Herner, A.E. in Pesticide Properties in the Environment , Springer-Verlag, New York, 1996; De Liñan, C. in Farmacología Vegetal , Ediciones Agrotecnicas S.L., 1997.
a 208C.
compounds are distributed in the plants by translocation from the root and foliage and protect the plants against infection by phytopathogenic fungi. They have a certain persistence in soil (Table 1.21).
1.4.5 M ISCELLANEOUS
CN
Cl
Cl
SCCl 3
Cl
CN
Cl
Captan
Chlorothalonil
28 Analysis of Pesticides in Food and Environmental Samples
TABLE 1.21 Chemical Names and Properties of Morpholine Fungicides
Water
Vapor
Solubility Half-Life
K ow mg=L in Soil Common Name
Pressure
log P (208C) (Days) Dodemorph
IUPAC Name
mPa (208C)
4-Cyclododecyl- 0.48 4.14 <100 73 C 18 H 35 NO
2,6-dimethyl morpholine
Fenpropimorph 3.5 4.2 4.3 15 –93 C 20 H 33 NO
Butylphenyl)- 2-methylpropyl]-2, 6-dimethylmorpholine
Tridemorph 2,6-Dimethyl- 12 4.2 1.1 14 –34 C 19 H 39 NO
4-tridecyl morpholine Sources: Data from Tomlin, C. (Ed.) in The Pesticide Manual, British Crop Protection Council, 2000;
http:==ec.europa.eu=food=plant=protection=evaluation=exist_subs_rep_en.htm; http:==www.epa .gov=opprd001=factsheets=; Hornsby, A.G., Wauchope, R.D., and Herner, A.E. in Pesticide Properties in the Environment , Springer-Verlag, New York, 1996; De Liñan, C. in Farmacología Vegetal , Ediciones Agrotecnicas S.L., 1997.
Captan and folpet are fungicides used in foliar treatment of fruits, vegetables, and ornamentals, in soil and seed treatments, and in postharvest applications.
Procymidone is a dicarboximide-derived fungicide with moderate systemic action. It is rapidly absorbed not only through the roots but also through the stem or the leaves. It is used for the control of storage roots of fruits and vegetables and it is effective for seed dressing of cereals. Table 1.22 summarizes the properties of various frequently used fungicides belonging to different chemical classes.