BUCKEYE DISEASES 121 



unsatisfactory results for two reasons : spray mixtures do not 

 act as efficiently if the foliage is drenched, and lime-sulfur 

 may cause burning. Dusting nursery trees with a mixture of 

 finely ground sulfur and powdered arsenate of lead, in the pro- 

 portion of ninety parts of sulfur to ten of lead powder, has 

 proved effective in controlling this disease. It may, therefore, 

 be assumed that dusting shade and ornamental trees will be 

 equally effective. For further directions on spraying and 

 dusting for the control of leaf-diseases, see page 357. 



References 



Stewart, V. B. The leaf blotch of horse-chestnut. Cornell Univ. 

 Agr. Exp. Sta. Bui. 371 : 411-419, pi. 10, figs. 85-92. 1916. 



Stewart, V. B. The leaf blotch disease of horse-chestnut. Phyto- 

 pathology 6 : 5-19, pis. 2-4, fig. 1. 1916. 



Powdery Mildew 



Caused by Uncinula flexuosa Peck 



The leaves of the buckeye and horse-chestnut are affected 

 by a powdery mildew, in eastern, southern and central United 

 States. The powdery white mycelium usually occurs only on 

 the under surface of the leaf in' diffused spots. The black 

 fruiting-bodies of the fungus are just visible to the unaided eye 

 and are found scattered over the mildewed areas late in the 

 summer. For a discussion of the general life history and methods 

 of control of powdery mildew fungi, see page 37. 



Curled Leaf-Blight and Witches'-Broom 



Caused by Exoascus cesculi (Ell. and Ev.) Patterson 



This disease is described on the California buckeye. It 

 occurs in several localities in California. The most noticeable 

 symptom is the production of many large witches'-brooms. 

 The leaves which are borne on the twigs composing the broom 



