^6o AGk I CULTURE OF MAINE. 



OTHER LEAF DISEASES. 



A new leaf disease of potatoes has recently been observed in 

 Maine, and whether or not it is of any importance is yet to be 

 shown. This was first seen on some plants grown by the United 

 States Department of Agriculture at Houlton last year, and 

 appeared again on their plots at Caribou this year. I have 

 since seen it in northern New York, and near Tacoma in the 

 State of Washington. The two slides shown were made from 

 material obtained in the latter state. For the lack of a better 

 term this has been called the "Streak disease." It is charac- 

 terized by a browning of the veins and tissues on the lower 

 side of the leaf. No parasite has yet been isolated from the 

 diseased area, yet there are certain characteristics about it 

 which indicate that it might be of a bacterial nature. 



There are a number of leaf troubles recognized by pathologists, 

 and known by the names of curly dwarf, leaf roll, mosaic dis- 

 ease, etc., the nature of which is not very thoroughly under- 

 stood. From a practical standpoint, however, we do know that 

 most of these troubles are carried by the seed, and that they are 

 pretty sure to grow worse if tubers which are grown from 

 plants which show these abnormalities are used again for seed. 



Therefore, tubers found to produce abnormal types of foliage 

 should be eliminated from the seed stock. If the number of 

 affected plants are few they should be dug and discarded 

 before they set tubers. If they are many, the entire field should 

 be sold for table stock, and a new lot of seed from a healthy 

 field be obtained. Leaf roll has only occurred to a slight extent 

 in Maine as yet, but it is rather serious in certain western states. 

 On the contrary, the mosaic disease which is characterized by 

 a peculiar mottling or calico appearance of the leaves is by no 

 means uncommon in the Green Mountain fields in this state. 

 With the exception of New York, I have seen it in no other of 

 the northern or western states. 



WART DISEASE OF THE POTATO. 



The illustration of the worst known potato disease is left for 

 the last. This is the wart disease, which, when it attacks a 

 tuber, entirely destroys it and converts it into an irregular, 

 coral-like mass in no way resembling its original shape or 



