Agriculture Reference
In-Depth Information
Mode of Action
Quinone reacts with the sulfhydryl groups of enzymes such as amylase
and carboxylase. This reaction interferes with their activity and, indirectly,
with other cellular processes such as oxidative phosphorylation. Chloranil
and dichlone have been discontinued and are no longer available in the U.S.
Toxicity
The quinone fungicides are of low to moderate acute toxicity with oral
LD
50
values (rat) of: chloranil 4,000, dichlone 1,300, and dithianon 638
mg/kg. Under some conditions, these compounds may cause severe skin irri-
tation in sensitive individuals.
Table 5.33
Commercial products containing quinone fungicides.
Active Ingredient
Trade Names
Chloranil
Spergon
Dichlone
Phygon
Dithianon
Delan
B. SYSTEMIC FUNGICIDES
1.
Organic Fungicides
Systemic fungicides are absorbed by the plant through the roots, leaves,
or seeds and translocated thoughout the plant. In this way the whole plant,
including new growth, is protected against fungal attack or an established fun-
gal infestation.
Phytotoxicity is a much more difficult problem to overcome with sys-
temics, because they are brought into intimate contact with the host plant.
Most of the early systemic fungicides (benomyl) showed translocation
through the xylem. However, pyrimidine systemic fungicides e.g., ethirimol
and dimethirimol, appear to move through the phloem.
a.
Oxathiins and Related Carboxanilide Compounds
Oxathiins are a group of heterocyclic compounds with interesting sys-
temic properties. Carboxin and oxycarboxin are examples of this group.
Carboxin was the first seed disinfection agent with systemic activity used
in cereals to control loose smut in barley. Today, newer fungicides have dis-
placed carboxin.
