146 MANUAL OF FRUIT DISEASES 



developed throughout the growing-season. In the spring the 

 pathogene renews activities; thus perpetuating itself from year 

 to year. 



Control. 



Spraying is said to offer little hope for the control of rough- 

 bark. In most cases it would be a tedious operation to attempt 

 eradication of all diseased twigs. On the other hand, the deci- 

 sion in this regard must rest with the grower who is especially 

 desirous of cultivating the Yellow Newtown in those apple 

 regions where the disease is most prevalent. The susceptibility 

 of the above-named variety should be borne in mind in contem- 

 plation of orchard planting ; the experience of the local growers 

 of this variety should be the guide in determining whether it 

 can be profitably grown in spite of rough-bark. 



REFERENCES 



Roberts, J. W. The rough-bark disease of the Yellow Newtown apple. 



U. S. Agr. Dept. Plant Indus. Bur. Bui. 280 : 7-15. 1913. 

 Roberts, J. W. A new fungus on the apple. Phytopath. 2 : 263-264. 



1912. 



OZONIUM ROOT-ROT 

 Caused by Ozonium omnivorum Shear 



The apple and pear particularly are likely to suffer from this 

 root-trouble occurring in the South and Southwest. To growers 

 in these regions it is probably best known as a cotton disease ; 

 however, it affects not only fruit-trees and cotton but also forest- 

 trees, vegetables, forage crops and weeds. The range of host- 

 plants is practically unlimited, a matter of no mean considera- 

 tion from the standpoint of control. 



Symptoms. 



Plants affected by this disease usually show threads of the 

 causal fungus on the roots. These threads are at first whitish, 

 then dirty-white or brown. If cotton shows the disease, then 



