34 MANUAL OF TREE DISEASES 



from bits of leaves or diseased twigs which were not burned. 

 The eradication measures, therefore, should be supplemented 

 by spraying or dusting, as the leaves unfold and grow to full 

 size. For large trees, these measures are expensive and are not 

 advised except under extraordinary circumstances. Directions 

 for spraying and dusting will be found on page 357. 



Powdery Mildews 



Caused by fungi of the family Erysiphaoese 



The leaves and sometimes the twigs and fruits of many kinds 

 of plants are attacked by the fungi of the family Erysiphacese, 

 which cause powdery mildews. One or more of these powdery 

 mildews attack the leaves of most kinds of deciduous trees in 

 the United States. Two species of these fungi, Microsphcgra 

 alni and Phyllactinia corylea, occur generally throughout the 

 country and may be expected on all kinds of broad-leaf trees. 

 The following list of the powdery mildew fungi reported in this 

 country on the different kinds of trees may be of interest, al- 

 though without the aid of a microscope no definite characters 

 are available for distinguishing one powdery mildew from 

 another : — 



Alder 



Erysiphe aggregaia (Peck) Farlow (on female catkins), see page 86. 



Microsphoera alni (Wallroth) Salmon 



Phyllactinia corylea Karsten 

 Ash 



. Phyllactinia corylea Karsten 

 Basswood 



Uncinula Clintonii Peck, see page 101. 

 Beech 



Microsphcera alni (Wallroth) Salmon 



Phyllactinia corylea Karsten 

 Birch 



Microsphoera alni (Wallroth) Salmon 



Phyllactinia corylea Karsten 



