Agriculture Reference
In-Depth Information
Toxicity
As stated above, diocap has a relatively low mammalian toxicity with an
oral LD
50
(rat) of 980 mg/kg and is assigned to Toxicity Category III with the
signal word “Caution.”
f.
Thiophthalimides (sulfenimides)
Introduced in 1949, captan has become one of the most popular and versa-
tile fungicides for foliar treatment of fruits, vegetables, and ornamentals, for
soil and seed treatments, and for postharvest applications. Captafol and folpet
were introduced later and were also used as dusts and sprays on fruits, vegeta-
bles, and ornamentals. Captafol and folpet were later discontinued by the
manufacturers because of their long-term health hazards.
Mode of Action
The fungicidal action of captan results from the toxic moiety or toxophore
N—S—CCl
3
. Studies suggest that captan interacts with the sulfhydryl groups
within fungal cells to produce thiophosgene. This highly reactive chemical
then reacts with free sulfhydryl, amino and hydroxyl groups of enzymes and
causes the inhibition of metabolic processes.
Toxicity
Captan has been classified in Toxic Category I because of the potential for
severe eye damage. Dermal sensitization may occur; captafol appears to have
been responsible for several episodes of occupational contact dermatitis. No
systemic poisonings by thiophthalimides have been reported in man (captan has
a very high oral LD
50
in rats of 9,000 mg/kg).
Table 5.32
Commercial products containing thiophthalimide compounds.
Active Ingredient
Trade Names
Captan
Captanex, Captaf, Drexel, Merpan, Orthocide, Vondcaptan
Captafol
Not marketed in the U.S.
Folpet
Not marketed in the U.S.
g.
Quinones
The first member of this group, chloranil, was first used as a fungicide in
1938. It was found to be useful as a seed protectant and foliage fungicide for
downey mildew. The more popular, related derivative known as dichlone was
used on a number of fruit and vegetable crops and for the control of blue-green
alge in ponds.
