376 Diseases of Economic Plants 



To destroy mistletoe the infected branches should be cut 

 from the trees and no berries allowed to mature, thus pre- 

 venting dissemination of the pest by birds. Razoumofskya, 

 the dwarf mistletoe, is represented by some eleven species in 

 the United States, parasitic on conifers, spruce, pine, fir, 

 hemlock, larch. Phoradendron, or the leafy mistletoe, 

 consisting of several species is found on practically all kinds of 

 broad-leaf trees. 



Witches-brooms. — The production of numerous adven- 

 titious buds may result in the close, broomlike branching 

 which gives rise to this common name. The condition is 

 prevalent on many kinds of trees, particularly so on the hack- 

 berry, which is rarely without the witches-brooms in profu- 

 sion. They are also common on horse-chestnut, juniper, and 

 fir. The cause of this abnormal branching is a stimulus im- 

 parted by insects (mites) , or by any one of several fungi as for 

 example: Taphrina, Gymnosporangium, Peridermium, or 

 the Powdery-mildews. 



Slime-flux. — This is a term applied to a condition in 

 which portions of the tree are covered by a slimy, fermenting, 

 wet, often foamy, flow. This usually originates in sap oozing 

 from a crack or other wound, often following surgical work, 

 and is most in evidence when the sap flows freely. The 

 organisms, yeast, bacteria, or their products, that induce the 

 fermentation, may cause death of neighboring cells of the 

 tree and result in a chronic wound, though the injury is at 

 most little more than unsightly. Excision and disinfection 

 may be practiced. 



Damping-ofif ^^' ^-' ^^® (Corticium, Pythium, and Fusa- 

 rium). — Coniferous seedlings chiefly are affected. Soil 

 disinfection by sulfuric acid, copper sulfate, zinc chlorid, or 

 formalin, or when practicable by steam, are advised. See 

 p. 460. 



Tree Surgery '">'■ ''-' ^"^^ ^'^ 



Ornamental, shade, and even nut and fruit trees are often 

 of value sufficient to warrant careful surgical treatment to 



