42 



window. It was a vei\y healthy specimen having grown about six feet 

 in a single year. It seemed to have escaped the leaf spot until rather 

 late in the season but when the disease did start it took only about 

 three weeks to cause all but a few of the leaves to droj). 



This fungus produces large crops of spores on the under surface 

 of the leaves and these are the source of further infection. In addition 

 the young twigs are attacked and it has been demonstrated in Europe 

 that spriiiig infection may take place from fresh crops of spores pro- 

 duced on these overwintering spots. But it is probable that infection 

 also takes place from the dead leaves beneath the tree since the fungus 

 lives over winter in these leaves and produces a crop of spores of 

 different character from those produced on the twigs and leaves. 

 These spores are capable of reinfecting the leaves in the spring. Little 

 is acti;ally known concerning the life history of this parasite and 

 one must guess as to the best methods of control. Undoubtedly any 

 practice which reduces the amount of shade in the orchard will aid 

 in reducing the amount of injury from this disease. Destruction of 

 the deid leaves underneath the tree during the winter or early spring 

 would probably be of benefit. Dormant spraying would probably be 

 of value since similar diseases on the other dormant plants are con- 

 trolled by this method. Summer spraying will control the disease but 

 the number and time of applications would have to be worked out 

 experimentally. 



It is evident from the above statements that we are sadly in need 

 of some experimental work on the control of nut diseases of this type. 

 I will take up this point later under some suggestions I have to make. 



As most of you know^ the butternut is a short lived tree. Many 

 explanations have been given for this fact. One is that of wood decay 

 while others believe that it is due to some special disease of roots. 

 JNIuch needs to be learned about this condition. 



All three of these nut trees suffer from other leaf spots. The 

 walnut has at least four others but none of them are of any great im- 

 portance so far as we now know. 



There are two powdery mildews on walnut and butternut and one 

 on hickory. These are seldiom serious but may prove of importance in 

 the orchard and are certain to cause trouble in the nursery. 



