THE POTATO IN BRITISH COLUMBIA. 



69 



The cause of this disease, like leaf-roll, is unknown. 



Control. The best means of control up to the present time is that of selection 

 of seed from districts where mosaic does not occur. 



Fig. 74. Plant on the left typical Mosaic; the 

 one on the right healthy (original). 



EARLY BLIGHT (Alternaria solani). 



This is so called because it usually first appears earlier in the season than late 

 blight. It appears as dark-brown spots on the leaves, which, typically, have a very 

 characteristic zoned or target-like appearance. The tips and margins of the leaf 

 may also be affected. Tubers are not directly attacked, but if the leaves are seriously 

 injured their development is checked. Spraying with Bordeaux is effective against 

 early blight, but must be done early, beginning when the plants are 4 inches high. 





Fig. 75. Skin-spot disease. Cause not yet determined (original). 

 TIP-BURN. 



The tips and edges of the leaves turn brown, curl up, and become crisp and 

 brittle, due to intense sunlight, especially after dull, cloudy weather. This is often 

 associated with early blight and is controlled by the same means; the covering of 

 Bordeaux mixture apparently screening out the rays of light most injurious to the 

 plant-tissue. 



