POTATO LEAF CURL 323 



PREVENTIVE MEANS. Spraying with a solution of 

 ammoniacal copper carbonate, or of potassium sulphide, 

 arrests the spread of the fungus. The wisest plan is to 

 remove diseased plants before the conidia diffuse, and by 

 picking off the leaves the formation of sclerotia is pre- 

 vented. If stems are also attacked they should be cut off. 



POTATO LEAF CUEL 



(Macrosporium solani, Cooke.) 



The well-known disease of the foliage of potatoes known 

 as ' leaf curl ' attacks the stem, usually close to the ground 

 at first, and gradually creeps up, first causing the leaves to 

 curl, and finally the stem also collapses. When the leaves 

 first curl, there is usually no external sign of the fungus, 

 but at a later stage the stem and leaves become more or 

 less studded with blackish, minutely velvety patches. 



These dark patches are due to the production of in- 

 numerable conidia on the surface of the host. The 

 conidia are large, olive-brown, and divided into numerous 

 cells by septa crossing at right angles. 



This fungus is closely allied to, if not identical with, 

 the Macrosporium causing ' black stripe ' or blotch on the 

 tomato. 



PREVENTIVE MEANS. The spores persist through the 

 winter on fragments of leaves and stems ; hence, to prevent 

 a repetition of the disease, it is essential the potato ' tops ' 

 should be carefully collected and burnt in the autumn. 



Spraying with dilute Bordeaux mixture, if commenced 

 sufficiently early, prevents the disease from doing serious 

 mischief. 



