Agriculture Reference
In-Depth Information
It was not until the middle of the nineteenth century that systematic scien-
tific methods began to be applied to the problem of controlling agricultural
pests. About 1850 two important natural insecticides were developed: rote-
none from the roots of derris plants and pyrethrum from the flower heads of a
species of chrysanthemum. These insecticides are still widely used. At about
the same time, new inorganic materials were introduced forcombating insect
pests. For instance, an investigation into the use of new arsenic compounds
led in 1867 to the introduction of an impure copper arsenite (Paris Green) for
control of the Colorado beetle in the state of Mississippi. In 1892 lead arse-
nate was used for control of gypsy moth.
The Irish Potato Famine of the 1840s illustrates what can occur when a
staple food crop is stricken by a disease against which there is no known de-
fense. The potato crop was virtually destroyed by severe attacks of thefungal
disease known as potato late blight, resulting in the deaths of more than a
million people.
Millardet, in 1882, accidentally discovered a valuable chemical treatment
for the control of pathogenic fungi, like potato blight and vine mildew. This
discovery came from a local custom of the farmers in the Bordeaux district of
France. They daubed the roadside vines with a mixture of copper sulfate and
lime in order to discourage pilfering of the crop. At this time the crops of the
French vineyards were being destroyed by the downy mildew disease.
Millardet observed that although the vines away from the road were heavily
infested with mildew, those alongside the road which had been treated with the
mixture were relatively free from the disease. Millardet subsequently carried
out further experiments which established the effectiveness of the mixture of
copper sulfate, lime, and water against vine mildew. The mixture, called the
Bordeaux mixture, was widely applied, the disease was arrested, and Millardet
became somewhat of a hero.
In 1897 formaldehyde was introduced for the first time as a fumigant. In
1913 organomercurials were first used as fungicidal seed dressings against ce-
real smut and bunt diseases.
W. C. Piver in 1912 developed calcium arsenate as a replacement for Paris
Green and lead arsenate. This mixture soon became important for controlling
the boll weevil on cotton in the United States. By the early 1920s the
extensive application of arsenical insecticides caused widespread public outcries
because fruits and vegetables treated with arsenates were sometimes shown to
contain poisonous residues. This stimulated the search for other less
dangerous pesticides and led to the introduction of organic compounds, such as
tar, petroleum oils, and dinitro-o-cresol. The latter compound eventually
replaced tar oil for control of aphid eggs, and in 1933 was patented as a
selective herbicide against weeds in cereal crops. Unfortunately, this
