DISEASES. 21 



Wilting. The leaves of shade trees frequently wilt out of season. 

 Sycamores are apt to lose their first leaves in the spring from a 

 prevalent disease, but soon get a second set and usually suffer lit- 

 tle permanently. No specific treatment is advised. Other species, 

 especially maples, are beset with lice or scale insects which by suck- 

 ing their juices cause the leaves to die. If the attack is slight let 

 nature take care of it ; if it is serious spray as directed on page 22. 

 But most trouble of this kind is found in Norway and sugar maples ; 

 the cause is obscure, yet there is reason to believe that too little food, 

 sometimes too little water, is available to nourish the heavy leafage 

 that these trees produce. Feeding and watering (p. 13) will usually 

 prevent this trouble ; if it develops, let the foliage of the affected tree 

 be curtailed by an interior pruning (p. 14), then fertilize. (Figs. 



8,9.) 



Bleeding. This frequently occurs when branches are cut while 

 the sap is moving freely. Under such conditions stop all pruning as 

 loss of sap lowers the vitality of a tree. 



Another sort of bleeding, sometimes called "slime-flux," and hav- 

 ing an offensive odor, usually begins in a wound, or behind a filling, 

 and is often hard to manage. Like a sore in the flesh the worst 

 possible course is to stop it from the outside ; it must be cleansed, 

 sterilized and made to heal from the inside. Let all affected tissue 

 bark and wood, be cut out with a sharp chisel, the wound pointed 

 at top and bottom (fig. 10) and all edges left smooth : sterilize the 

 exposed surfaces with weak formalin and cover with tar; never 

 use cement. If the trouble is due to a split crotch, clean the crack 

 as well as possible, bolt the parts together, as at D, figure n, and 

 treat as above. 



Insects . 



Not all insects are harmful to trees: some, tho harmful, are so 

 controlled by natural enemies that they rarely are found in num- 

 bers great enough to do serious damage; others attack only trees 

 that have been weakened by neglect or injury. 



As with diseases, harmful insects usually confine their attacks 

 to trees of one species, or one genus. Thus the elm beetle attacks 

 elms only, the hickory borer only hickories. It is entirely safe to 

 say that a few insects of any kind on a vigorous tree will do little 

 harm ; a few insects on a weak tree should be looked after, and many 

 insects on any tree demand prompt attention. But to be always on 

 the safe side every suspected case should be referred to some au- 

 thority an entomologist or a forester. Ants are rarely harmful ; 

 their presence about a tree usually means that honey dew, decayed 

 wood or fungus growths are available for their food. 



Injurious insects are grouped in three classes: biters, suckers, 

 and borers. 



