 All
over the world, an incessant war is being waged against animal diseases
which attack cattle and sheep, as well as the fungus growths, moulds,
microbes and insect pests that decimate crops. In this struggle, many
kinds of treatment are needed because what is effective in some diseases
may be quite useless in others. Spraying and dusting are the most
common remedies, and copper compounds are a constituent of many of
the powders and solutions used.
Much information on this vital subject can be found in the Copper
Development Association's (CDA-USA) Publication No. 41, Copper Compounds
in Agriculture and Industrial Microbiology, from which the following
statement is taken:
"The earliest commercial use of copper was in the form of sulphate
as a seed dressing to destroy cereal diseases. Much later it was discovered
that copper sulphate also prevented foliage diseases. If applied in
too strong a solution it damaged the foliage but, by mixing with lime,
Bordeaux Mixture was formed, and this has excellent adherence to foliage.
This mixture enables plants to be provided with a protective coating
of copper which prevents the penetration of the spores into the tissues.
As long as the copper deposit remains on the tissue protection is
maintained."
The most serious disease treated in this manner is potato blight,
and neglect to spray the crop can be disastrous. Tomatoes are also
sprayed against blight; raspberries and currants against leaf-spot;
stone-fruits, hops and vines, citrus fruits, bananas, and tea (against
blister blight); coffee (against rust and blight); and tobacco (for
wildfire).
Probably, about 200,000 tons of copper sulphate are used in the world
every year for these and similar purposes. In addition, smaller quantities
of other copper compounds are applied, such as copper oxide, oxychloride,
and the copper-arsenic compound known as Paris Green.
Minute quantities of copper are essential to life; hence it is the
practice on poor peaty or sandy soils deficient in that element to
add copper sulphate to the usual fertilizer, thereby increasing the
yield of the crops. For similar reasons 'salt licks' are provided
for sheep to prevent the disease of lambs known as 'sway-back', and
for cattle and other grazing animals. The dangerous tropical disease
bilharzia, which is due to a minute animal parasitic on snails, is
also controlled by treating infected streams and lakes with a copper
sulphate solution. Liver rot in sheep, due to flukes in another water-snail,
is also treated by applying copper sulphate to the infected ground.
Thus, in the 20th Century we have turned the complete circle. Industry
began when people picked up shining pieces of copper and wondered
what they were. We concluded with the century by replenishing the
same element, by applying it to soils and feed from copper solutions
sprayed out of a watering can. |
