378 



UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



and disinfected with some success, but the trouble cannot be entirely 

 overcome in this way. Usually decay sets in, as shown in the illustra- 

 tion, and the tree eventually breaks off. 



FIG. 94. Crown gall. 



ROOT ROT. 



(OAK FUNGUS TOADSTOOL DISEASE.) 



The English walnut root is quite susceptible to the so-called oak 

 fungus or toadstool disease, which occasions the loss of many fruit 

 trees of various kinds in California. This disease consists in a decay 

 of the roots, in which the white mycelium of the fungus may be found 

 between the affected bark and wood. Occasional clusters of toadstools 

 appear at the base of affected trees. The disease usually, if not always, 

 occurs in spots where oak trees formerly stood and when once started 

 spreads from tree to tree in quite a regular concentric manner. 

 Experience has amply demonstrated that our native black walnut roots 

 are immune to this fungus and we have seen cases where English walnut, 

 prune, almond and other roots have been picked out and killed, while 

 northern California black walnuts interplanted with these trees 

 remained entirely unaffected. It is altogether probable that all of our 

 black walnut species and hybrids are highly resistant if not totally 

 immune to this disease. 



