Agriculture Reference
In-Depth Information
still a valuable disease control measure today. Bordeaux mixture is a simple mixture of
copper sulfate, hydrated lime, and water.
7
The mixture is affordable and effective for
many types of diseases infecting leaves through spores. It will not cure a disease
within a leaf or stem.
10.13.3 Curative Treatments
Once an insect or disease has established itself in a field and the threat for economic
damage is clear, the farmer must attempt to limit the damage. At this stage the
farmer almost always resorts to chemicals to kill the insects or disease.
Insecticides can be divided into three groups based on the feeding habits of the
insects to be controlled. If an insect eats the leaf of the plant (most caterpillars), then
a poison can be applied to the surface of the leaf. When the insect eats the leaf, it
will also eat the poison and be killed. If the insect damages the plant by sucking the
sap from the leaves or stems (aphids), a systemic insecticide must be applied. These
penetrate the plant and circulate in the sap within the stems and leaves. A few insecti-
cides depend on direct contact with the insect.
In all cases, use of chemical insecticides is a last resort. Continuous use of chemi-
cals to control an insect problem often results in a buildup of insecticide-resistant insect
populations. A small valley in the Andes of Ecuador had a problem with whitefly on
tomatoes. Farmers had used various chemicals to kill this sucking insect, but after a
few years it seemed the insects came back even sooner after the spraying. Then the
farmers tried mixing two, three, even four insecticides together in a formula they
called la bomba at ´mica (shown in Fig. 10.19) in an attempt to finally eradicate the
whitefly. Of course, the insects finally evolved resistance to this mixture and the
problem was worse than before.
There are few chemicals available to cure bacterial or fungal diseases after they
have infected the plant. With diseases caused by a virus, the only remedy is destruction
of the infected plants. This usually consists of pulling out the diseased plants, gathering
them together, and burning the remains.
10.14
ELECTRICITY
While crops and animals do not directly use electricity, their production often depends
on a dependable supply of electric current. The warmth provided by an electric light-
bulb shown in Figure 10.20 is enough to keep young chicks warm while their feathers
develop. Without electricity the farmer would need to use a kerosene heat source that is
a fire danger and could possibly asphyxiate the birds.
Electricity is used in the farmer's home to provide light at night and in the farm
buildings to feed animals after dark. In Ecuador the sun sets between 6:15 and
6:30 p.m. (it is on the equator) and nearly 12 hours of each day are dark. Electric
lights help lengthen the day to finish chores. In the United States we are much more
dependent on electricity. Farmers use electric pumps for watering livestock, to
charge batteries, to power milking machines, repair machinery, and to make their
