MAINE AGRICULTURAL EXPERIMENT STATION. II 



without the potato growers knowing the difference between it 

 and common scab. Yes, without knowing that such a thing as 

 powdery scab existed. 



Potato leaf-roll, as its name implies, is characterized by a 

 conspicuous upward rolling or curling of the leaflets on their 

 mid-ribs. The leaves assume a more upright position than is 

 normal. A striking characteristic of the disease is the change 

 in the color of the leaves. This is a yellowing, frequently asso- 

 ciated with a reddening or purpling. I was by no means al- 

 ways satisfied that much of what was pronounced to be leaf- 

 roll, even by the experts of the party, always occurred entirel> 

 independent of other disease producing factors. After a cer- 

 tain amount of familiarity with the disease was acquired, two 

 important characteristics were observed, which, if present, 

 tended to eliminate any doubt which existed. One of these 

 was the appearance of the reddish and purplish colors in the 

 curled leaves, and the other was the almost entire failure of the 

 affected plants to set tubers. I know of no other potato dis- 

 ease where these characters are of constant occurrence to- 

 gether. 



Plants affected with leaf-roll .are more or less stunted in 

 appearance. They appear much longer lived than those at- 

 tacked by wilt, and may live as long as the healthy plants in 

 the same field. Apparently it is a non-parasitic trouble, though 

 in some cases it has been maintained that it is caused by fungi. 

 Leaf-roll is carried by the seed tubers, hence those produced 

 by diseased plants should not be used for seed purposes. 



Although fields have been reported in Maine as carrying as 

 high as ioo per cent of the disease, I personally have seen al- 

 most none of what I should call true leaf-roll in this state. I 

 have, however, seen a trouble of similar appearance associated 

 with Rhizoctonia injury which might easily be mistaken for it. 



Plants affected with what is known as curly dwarf have 

 every appearance that the name implies. The whole plant is 

 dwarfed and more compact than normal and has a peculiar 

 crinkled foliage. An important characteristic of the disease is 

 that the stems and leaf petioles are distinctly brittle as com- 

 pared with those of normal plants. As compared with leaf- 

 roll the leaves curl downward rather than upward. Occasion- 



