Insect and Disease Control 259 



effect on these parts as a rule is relatively unimportant, 

 though the small twigs are sometimes killed thereby. 



Course of development. 



The affected leaves gradually turn yellowish, finally 

 blacken and drop off, though in the course of these changes 

 certain areas of the leaves assume a mealy or frosted ap- 

 pearance, due to the growth of the spores by which the disease 

 is perpetuated. The disease works largely in early spring, 

 as the new leaves are developing. The occurrence of cold 

 damp weather is favorable to its development and in some 

 cases the early infections result in affected trees becoming 

 entirely defoliated. This depletes the vitality of the trees, 

 and where it occurs for several seasons in succession, they 

 become weakened thereby to a serious extent. 



Methods of control of curl. 



Apparently the leaves become infected as soon as they 

 begin to unfold or possibly even before, since spraying after 

 the foliage is partially developed has little or no effect in 

 controlling the disease. Trees that are systematically 

 sprayed during the dormant season, especially shortly be- 

 fore the buds begin to open in the spring, with lime-sulfur 

 mixture (dormant strength) for San Jose scale do not or- 

 dinarily suffer from this trouble. When spraying is done 

 for this disease alone, bordeaux mixture applied very 

 thoroughly about two weeks before the buds open seems to 

 give the highest measure of protection ; in fact, it usually 

 holds the disease in practically complete control. Or the 

 lime-sulfur preparations applied at this time or during the 

 winter, or even in November or early December, usually 

 give a high degree of protection. 



