CoLOKADo Plant Diseases 
21 
PART II 
DISEASES AFFECTING COLORADO CROP PLANTS 
On account of the fact that no adequate survey of the plant 
diseases of the state has ever been made, the distribution, prevalence 
and severity of many of the diseases in Colorado are not known with 
any great degree of accuracy. Limited observations on the part 
of the writer and the fragmentary reports that have been received 
from time to time are the only sources of information available at 
present. 
A survey of plant diseases in Colorado has been started, however, 
in co-operation with the office of Plant Disease Survey, of the 
United States Department of Agriculture, and it is hoped that within 
the next few years much valuable data wdll be collected on this 
subject. 
In the following discussion no attempt has been made to treat 
all the diseases that occur on crop plants in Colorado. Only those 
known to be of considerable economic importance have been de- 
scribed. On the other hand a few diseases are included that have 
not yet been found in the state but which, on account of their 
serious nature and the liability of their introduction, it was thought 
best to mention at this time. 
The crops are arranged alphabetically and the diseases of each 
are treated in somewhat the order of their relative importance. 
The figure in parentheses just following the name of the disease 
refers to a bulletin, which gives a more complete discussion of the 
trouble. The list of bulletins will be found at the back of this 
publication. 
ALFALFA 
Bacterial Blight (Pseudomonas medicaginis) (1) — This is one of 
the most serious diseases of alfalfa in Colorado, and is widely dis- 
tributed over the southern half of the state. 
Affected plants are stunted and lighter green in color than 
normal. Infection is chiefly on the stems. In early stages the stem 
has a watery semi-transparent, yellowish to olive green appearance 
along one side. A sticky amber liquid oozes from diseased tissue 
and soon dries to form a shiny cast which becomes black with age. 
Where the ooze collects in drops, light amber colored scales are 
formed. Affected leaves are water soaked and pale yellow in color. 
!I!olored Plate on opposite page shows the bacterial blight of alfalfa. Original was 
used in Bulletin 158, by Sackett. 
