Agriculture Reference
In-Depth Information
from infected fields in the southern United States to start the next cycle of rust infec-
tions in the north.
Another method commonly used to reduce disease and insect problems is to destroy
the stems and leaves from the previous crops. The preferred way is to cover these resi-
dues with soil (plowing) so that decomposition will destroy the eggs and spores. In some
areas of the world burning is still practiced. This is effective but causes loss of soil
organic matter and nutrients as well as increasing erosion. In spite of these disadvan-
tages, it is still practiced in parts of the Sahel, Asia, and the United States.
A common way to reduce insect and disease problems is by crop rotation. If corn
borers are a problem, planting soybeans for 2 years will deprive them of food and
reduce the population to manageable levels. Nurseries with nematode problems (a
microscopic worm in the soil) will often plant marigolds to cause the nematode cysts
to hatch. Since nematodes cannot feed on marigolds they will die by starvation and
the total population in a field is dramatically reduced.
Use Varieties of Crop Resistant to Insect or Disease.
Using a variety of the
crop that is resistant to the insect or disease is an extremely cost-effective way to
manage a problem. Normally, the seed costs the same or slightly more than varieties
that are not resistant. Just planting a different seed solves the problem. This has been
the most successful approach to control diseases. Improved wheat varieties sold
around the world have resistance to wheat rust. Browsing through any sales brochure
for varieties of a crop reveals a long list of diseases for which each variety is more
or less resistant. Because diseases mutate, new resistant varieties must be constantly
developed to maintain production.
Development of insect resistance has been less successful using conventional
breeding techniques. With the release of genetically modified organism (GMO)
crops, insect resistance has become something farmers can expect. The release of
cotton varieties in China that make their own insecticide (Bt trait) has dramatically
reduced use of insecticides and costs of production. The farmers only need to buy a
different seed and their boll weevil problems are greatly diminished but not eliminated.
A problem with insect-resistant crops is that 20 percent of the field must be planted to
non-GMO crop plants as a “refuge.” This prevents a buildup of Bt-resistant insects by
giving them something to eat and survive. So there is no magic bullet to prevent insect
damage to crops. The best solution to date is to reduce damage to minimal levels.
Apply Preventive Treatments.
Certain insecticides are applied to seeds before
planting. These work only against insects in the soil that eat the roots of the seedling.
The corn rootworm is an example. These insects will eat away much of the root system
of a young maize plant. If the seed is treated with insecticide, the worm will only eat
enough of the insecticide to kill it. If an insect does not eat the roots of the seedling,
there is no effect. Seed treatment is an efficient way to prevent damage to young
plants but does not protect mature plants.
Applying chemicals to prevent a disease is possible but may be expensive. One
chemical that has been used for many years to control disease is Bordeaux mixture.
This was developed in France in the 1860s to control leaf diseases in vineyards. It is
