204 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 



We have found that potato stems showing the Corticium stage 

 usually, but by no means always, present some evidence of at 

 least old lesions somewhere on the parts below ground. We 

 have some reason for thinking that the Corticium stage may 

 occur with considerable regularity on the stems of the more 

 resistent varieties of potatoes without any evidence of injury. 

 This, however, in no way weakens the contention that the 

 fungus may be and is, under certain soil conditions and with 

 certain varieties of potatoes, an active and very injurious para- 

 site. 



During the latter part of August the potatoes on the field 

 tinder consideration began to take on an appearance similar to 

 normal ripening and this developed with considerable rapidity 

 so that by September 8 all the plants were dead. Different 

 parts of the field had been sprayed differently and a portion 

 Avas only sprayed with an insecticide to kill the potato beetles. 

 The strip which received no fungicide lived nearly as long as 

 one which had been sprayed with bordeaux mixture every lO 

 days or two weeks after about the first of July, using 4 spray 

 nozzles per row and applying over 200 gallons per acre at each 

 application. Hence the early death of the tops could in no way 

 be attributed to attacks of leaf diseases- Moreover, the adjoin- 

 ing field of Green Mountains, which showed a much smaller 

 percentage of plants attacked by Rhizoctonia, and none of these 

 severely, remained green till frost came a month or more later. 



The crop of Irish Cobblers was harvested as soon as possible 

 after the tops died and at this time a careful study was made 

 of the effects of the fungus upon the tubers. The most striking 

 characteristic to be noted by the casual observer was the abnor- 

 mal number of small potatoes produced. Hills were frequently 

 found where the yield was similar to that shown in Fig. 69. 

 Apparently tubers of all sizes, varying from those just formed 

 to those weighing half a pound or more were cut off from the 

 main stem by the fungus. As has already been stated, in many 

 cases the fungus followed along the tuber bearing branches of 

 the stem and attacked the young potatoes themselves. 



The appearance of such tubers was very characteristic. The 

 lesions were at the basal ends and always surrounded the point 

 of attachment of the tuber with the stolon. In mild cases there 

 was simply a browning of the surface closely resembling the 



