Agriculture Reference
In-Depth Information
physiological processes, and the fungus is an infection within the plant, it is
almost impossible to discover a completely nonphytotoxic fungicide that
would specifically block a process or reaction in one without effecting the
other.
Fungicides may be applied to seeds, foliage, or fruits as sprays or dusts.
For a dust to be effective, it must provide uniform coverage, and this requires
a small particle size. Spraying is the more widely used method of application.
The fungicide may be applied in solution or as a fine suspension and, there-
fore, the reduction in particle size increases the effectiveness of the fungicide.
1.
Inorganic and Organic Metal Fungicides
The earliest fungicides were inorganic chemicals like sulfur, copper, and
mercury.
a.
Sulfur
Sulfur alone and in combination as lime-sulfur was one of the most im-
portant fungicides. In the 1800s and early 1900s, sulfur dust and spray were
used against mildew on fruit trees. In 1958, the weight of sulfur used against
fungi was four times that of all other fungicides. However, the recent devel-
opment of organic fungicides has reduced the use of sulfur along with other
inorganic chemicals.
There are three formulations of sulfur used predominantly today. The first
is finely ground sulfur mixed with 1 to 5 percent talc or clay to assist in the
dusting effectiveness. The sulfur in this form may be used as a carrier for ad-
ditional pesticides. The second form is colloidal sulfur that is so fine that it
must be formulated as a paste to enable it to be mixed with water. The third
form is wettable sulfur. In this formulation the sulfur is finely ground with a
wetting agent so that it will mix readily with water for spraying.
Mode of Action
There has been much speculation regarding the mode of action of sulfur.
The current view is that sulfur itself (S
8
) may be toxic to fungi. Recent stud-
ies indicate that sulfur is not biological inert and probably becomes involve in
biological redox reactions. These studies also suggest that sulfur can more
easily penetrate spores in the presence of urea, hydrocarbons, surfactants, and
lime.
Toxicity
Sulfur in many of its formulations is relatively nontoxic. However, some
formulations may slightly irritate the skin.
