Nov. io, 19*3 
Two Diseases of Udo 
275 
took place considerably in advance of the hyphae, showing that this was 
due to an enzym, no doubt a pectinase. The browning of the vascular 
bundles before the appearance of the hyphae was especially noticeable, 
although their cells did not seem to lose coherence, at least to the same 
degree as did the pith cells. This fact seems to indicate the presence of 
some toxic substance. 
In the infected roots practically all of the tissues appeared to lose their 
coherence to a greater or less degree; the epidermis, however,remained 
intact. A large quantity of sap could be squeezed from the decayed root. 
Little if any change in the color of the root took place, even when it was 
entirely decayed. The decayed tissues of the root, as well as those of 
the stem, were filled with mycelium. Sclerotia of varying sizes and 
shapes, at first white, but gradually turning black, were found through¬ 
out the diseased root and stem, as well as on their surfaces. The 
decayed tissues eventually disintegrated, leaving the sclerotia in the 
soil. 
Probably insects and rodents are the chief agents in distributing this 
fungus, although it is possible that the fungus growing saprophytically 
in the soil may gain entrance to the roots through root hairs, dead root¬ 
lets, or wounds made during cultivation or cutting. 
CONTROL 
The control of diseases caused by species of Sclerotinia has proved to 
be difficult, especially under field conditions. Where the crop is grown 
in the greenhouse or can be subjected to cold-storage conditions the 
problem of disease control is greatly simplified. However, the udo is 
strictly a field crop and, being a perennial, is grown continuously in 
the same field for several years. The practicability of crop rotation as 
a control measure is therefore not great. It is quite obvious, however, 
that certain useful precautions can be taken. Should the causal organism 
prove to be Sclerotinia libertiana , as the writer believes, its distribution 
in this country is very general, and its available hosts many and various. 
Obviously, therefore, it is difficult to obtain land free from the fungus on 
which to start a planting. For growing udo care should be exercised to se¬ 
lect land on which no plants known to be susceptible, such as lettuce, celery, 
cabbage, carrots, and still others have been grown for a number of years. 
It is a wise precaution to have the udo planting some distance away from 
trucking centers, where so many susceptible hosts are grown. The plants 
should preferably be grown from seed, thus eliminating the danger of 
carrying the disease to the new planting on old roots. The disease may 
be brought to the field in particles of soil on cultivators or other tools, or 
by man or animals. Since a majority of infections probably occur through 
wounds, precautions should be taken to avoid wounding the plants 
during cultivation, by cutting young shoots or otherwise. Plants which 
have become infected should be taken up at once, all diseased parts 
should be eliminated, and any soil which may contain sclerotia or myce¬ 
lium should be removed. If the disease is detected in its early stage and 
the plant taken up at once before sclerotia are formed, there will be less 
danger of scattering the fungus about the field. By observing these 
precautions the grower should be able to keep the disease fairly well 
under control for some time. When once the land becomes infested 
the growing of udo upon it should be discontinued, at 4 east for several 
years. 
Nothing is known regarding susceptible or resistant varieties. 
60377—23 - 3 
