CHAPTER XXXI 



WALNUT DISEASES 



The walnut is commonly attacked by leaf-spot diseases which 

 may cause defoliation. The common white wood-rot and the 

 brown checked wood-rot sometimes are found in walnut. Com- 

 pared with many other kinds of deciduous trees, the walnut is 

 rarely affected by important diseases. The native black wal- 

 nut is Juglans nigra. The walnut of commerce, usually 

 called " English " walnut, is J. regia. Other species are in 

 cultivation. 



Leaf-Spot 

 Caused by Marssonia juglandis (Ldb.) P. Magnus 



This leaf-spot is also common on butternut. The spots are 

 irregular in shape and dark brown (Fig. 15, page 123). In some 

 seasons these spots become abundant and the leaves fall. This 

 leaf-spot is more fully described under butternut diseases, on 

 page 123. 



Common White Wood-Rot 



Caused by Fames igniarius Fries 



The wood of the black walnut is sometimes reduced to a white 

 punk by the false-tinder fungus. Beech, poplar, oak and maple 

 are commonly affected by the same fungus. The sporophores 

 and the nature of the decay are similar for all the kinds of trees 

 affected and are described under poplar diseases, on page 305. 



339 



