Agriculture Reference
In-Depth Information
canopy closure, weeds often get ahead of the crop. For situations like the one shown in
Figure 10.18, the only solution is to kill the weeds.
10.13.2 Preventive Treatments
From past experience a farmer will know if there is a good chance of insects or diseases
attacking the crop. Some insects are endemic to an entire region as are soil-borne dis-
eases. For these it is not a question of waiting to see if a problem will develop: it is
certain. In this case it is better to prevent the attack than to wait until the insect or
disease has built up in the field. There are several preventive tactics a farmer can use
to diminish yield losses from insects and diseases.
Reduce Source of Spores or Insects.
Prevention is always cheaper than trying
to cure a problem. Knowing the life cycle of a disease or insect can help to reduce its
effect on a crop. For example, the wild barberry bush is often infected by wheat rust.
The disease does not kill the barberry but remains dormant over the winter in the north-
ern United States. In spring spores develop and are carried by winds to wheat plants in
fields. Soon many wheat plants are producing more spores to infect other plants in the
field and an epidemic can destroy the crop. Removing wild barberry plants from areas
near fields is one way to reduce the severity of rust attacks in wheat fields. This has been
practiced since the 1600s in Europe. Starting in 1918 in the United States a program
was put into place to eradicate wild barberry as a means of reducing wheat rust. This
was effective in preventing early infections of wheat fields in the northern United
States but did not completely eliminate wheat rust. Enough spores were blown north
Figure
10.18.
Weeds competing with maize.
