10G SHADE TREES. 



Treatment. 



The only practical method of control consists in cutting 

 and burning diseased parts. 



BLACK KNOTS. 



These unsightly growths occur on the twigs and leaves of 

 some trees. Among the most important are those on the 

 plums and cherries which are caused by the fungus (Plow- 

 rightia morbosa Sacc.), and those upon the hazel caused by 

 the fungus (Cryptosporella anomala Pk.). 



Treatment. 



They are of no very great importance 011 shade trees, but 

 can be controlled by cutting out and burning early in the 

 fall and by spraying with copper sulphate or lime-sulphiu* 

 before the buds open in the spring. 



WITCHES' BROOMS. 



These conspicuous and unsightly growths are quite com- 

 mon and are due to the attacks of both fungi and insects 

 which cause the formation of masses of short twigs and are 

 sometimes mistaken for mistletoe growths. (See page 107.) 

 The most common and most conspicuous is the one on the 

 hackberry. (Celtis occidentalis L.) This is so common 

 that it is extremely difficult to find a tree that does not have 

 them, and many people consider them a characteristic growth 

 of the hackberry. However, they are a disease, and if the 

 tree is kept free from them, it makes a very beautiful growth. 

 The disease is said to be due to two parasitic organisms, a 

 powdery mildew (Spcerotheca phytoptophila Kell and S. AY. ) 

 and a mite (Eriophyes sp.) 



