APPLE DISEASES 147 



apples and other trees in close proximity are likely to become 

 afflicted. The disease is recognized on cotton by a sudden 

 wilting, usually during the latter part of June or early July, 

 such symptoms being exhibited by isolated plants here and there 

 in the field. 



Apples affected with Ozonium root-rot show a sudden wilting 

 and death of the leaves; this is particularly characteristic of 

 young trees. In case of old trees death is more gradual. In 

 general affected trees have an abnormal, sickly appearance for 

 a year or more prior to actual death. The causal fungus 

 surrounds the tap root as well as the lateral roots; such 

 roots die, decay, and thus cannot function, either in lending 

 mechanical support to the tree or in furnishing the top with 

 water and food. 



Cause. 



Numerous theories have been advanced by growers to explain 

 the causal relationships of the Ozonium root-rot. But, as al- 

 ready intimated, the fungus Ozonium omniwrum creates the 

 disturbance. It lives and spreads in the soil and seems to have 

 a decided preference for the Houston clay or black waxy soils 

 of the Southwest. The fungus grows best where soil aeration 

 is the poorest. A high temperature and plenty of moisture are 

 favorable to its development. Therefore the hot weather of 

 the South favors it ; and it flourishes where there is excessive 

 water of irrigation, if other conditions are favorable. 



Once in the soil the fungus is washed about, and finally a root 

 is encountered. The bark and woody tissues are penetrated, 

 their cells being killed as the mycelium proceeds; ultimately 

 decay is the result. After its work is complete, the mycelium 

 breaks up into segments which are washed away to other roots 

 of the apple or other plants. It may also spread by growing 

 through the soil on decaying material, or may be carried by 

 tools used in cultivation. No special fruiting bodies are 

 known. 



