Colorado Plant Diseases 
81 
All of Cereals in this country. The White Pine Blister Rust made 
its appearance in a small isolated area in Northern Minnesota a few 
years ago. Intensive efforts are now being made to eradicate the 
disease in that area. The Barberry Eradication Campaign being 
carried on by the U. S. Department of Agriculture is a good example 
of eradication on a large scale. Eradication methods may also be 
used on a small scale in eradicating diseases that have gained en- 
trance into such places as greenhouses, hot beds, etc. Soil steriliza- 
tion by steam or formaldehyde are the processes usually employed. 
Protection 
The old adage that “an ounce of prevention is worth a pound 
of cure, ’ ’ is extremely applicable to plant diseases. Few plants that 
have once become affected with a disease can be cured by treat- 
ment as is the case with men and animals. Plants must be protected 
from infection by disease producing organisms. 
The most practical plant disease control measures come under 
this head. The common means of protecting plants from the attacks 
of parasitic organisms are as follows: (1) Good cultural practices, 
(2) Crop sanitation, (3) Crop rotation, (4) Seed selection and seed 
treatment, and (5) Spraying. 
Good Cultural Practices 
There are a large number of disease-producing organisms which 
can attack plants only when they are in a weak condition. Since 
proper cultural methods tend to produce healthy, vigorous plants 
this alone in some cases is adequate protection from the disease. 
Moreover, certain physiological diseases are produced as a direct 
result of improper cultural methods. Better cultural practices would, 
of course, protect the plant against these troubles. 
Crop Sanitation 
Since most parasitic diseases are spread by the scattering of the 
causal organism from a diseased to a healthy plant, the removal and 
destruction of diseased plants or parts of plants is a very important 
means of protecting the healthy plants. The practicability of this 
method is, of course, determined by the nature of the disease to 
be controlled. 
Crop Rotation 
Many disease-producing organisms live from year to year in the 
soil but only become sufficiently plentiful to injure the crop when 
the plant is grown for several years in succession on the same soil. 
