potato diseases *n i907. 323 



Black Leg of Potatoes. 



Late in July the Station Entomologist noticed that many of 

 the potato stems on one field at Sherman were blackened and 

 decayed at the base. Examination of the specimens which she 

 collected showed that they were affected with what is known 

 in England as "black leg." This is a disease, or more likely 

 in the present case, one of a class of similar potato stem diseases 

 which has begun to attract considerable attention in America 

 within the past few years. It has not been previously reported 

 from Maine, and so far as the writer can learn was first credited 

 to New England by Jones in 1906.* It is interesting to note 

 that he makes the following statement with regard to the seed 

 used on the field where the outbreak occurred : "The field was 

 planted with Green Mountain potatoes, the seed being from 

 Houlton, Maine." 



The field in Sherman where the diseased stems were first 

 found was visited with Miss Patch on July 30. This was on 

 rather low land which had recently been cleared, having never 

 been under cultivation before. The field where the seed was 

 grown was some miles away and planted to another crop, there- 

 fore no attempt was made to discover if the disease occurred 

 on the original field. However, as will be seen later, there is 

 some reason to think that the disease is carried with the seed. 

 Affected plants were scattered all over the field, but probably 

 less than one per cent of them were involved. When the field 

 was examined, and in fact the same is true of all the fields seen 

 later, the disease had apparently passed its greatest period of 

 activity and was now on the decline. Affected plants could 

 usually be detected some distance away. Their leaves were, 

 as a rule, of a lighter green or yellowish color, especially in 

 the later stages of the disease. The diseased plants were almost 

 invariably more compact than the healthy ones, due to the 

 upward trend of the lateral branches and petioles. The leaves 

 also tend to curve upward, the younger ones folded upward 

 along the midrib. Occasionally small green tubers could be 

 found on diseased plants growing in the axils of the leaves 

 above ground. Careful observation showed that any one of 



* Jones, L. R., Vt. Sta. Rept. 19, p. 257 (1906). 



