202 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



Plants attacked by Rhizoctonia at the stage described above 

 may be readily distinguished from those affected by blackleg 

 when they are dug up. The latter always show inky-black dis- 

 colorations of the stem and the disease always starts at the 

 bottom at its junction with the seed-piece and works upward 

 through the stem. In the case of the Rhizoctonia trouble the 

 diseased areas are brown in color, may occur anywhere on the 

 stem below ground, and work from the surface inward. In 

 later stages, where the attacks of Rhizoctonia have not been 

 sufficiently severe to cause the early death of the plant a large 

 part of the surface of the diseased stems below ground may 

 become browned. 



About the middle of July a large number of hills, so selected 

 as to give as accurate sample as possible of the entire field, were 

 uncovered in an endeavor to estimate the per centage of plants 

 affected at that time. Fully 50 per cent showed the slightly 

 sunken, brown lesions, overrun with Rhizoctonia threads, vary- 

 ing in size from a mere dot to those which covered from two- 

 thirds to three-fourths of the under-ground surfaces of the 

 stems. 



A similar examination was made on August 4, taking care 

 that a different but equally representative lot of plants was 

 selected. By careful estimate 91 per cent of the stems showed 

 evidence of the attacks of the Rhizoctonia fungus below ground. 

 (Only about 17 per cent of the Green Mountain plants on an 

 adjoining portion of the same field at this time showed evidence 

 of similar lesions below ground. Here the attacks were not 

 serious and apparently the damage was slight. The latter con- 

 clusion was confirmed when the crop was dug). At this time 

 the plants were large and the tops nearly covered the ground. 

 The gaps made by the previous death of the more severely at- 

 tacked plants were entirely obscured by the growth of the 

 others. To the average observer this looked like a healthy and 

 exceedingly promising potato field. A careful inspection re- 

 vealed the fact that slightly abnormal plants, showing a clus- 

 tering of the leaves or a suggestion of a rosette effect were by 

 no means uncommon. 



In many instances the stems gave evidence of partial recovery 

 as the plants grew older, the lesions appeared to be healed, 

 showing simply a dark, russeted surface. In more severe 



