54 MAINE AGRICULTURAL EXPERIMENT STATION. 



tempted, corrosive sublimate should be used as formaldehyde 

 i': not entirely effective upon it. 



The injury is all below ground and the plants may be at- 

 tacked at any time after the sprouts begin to start from the 

 seed pieces. The sprouts which are attacked first or most 

 severely, either never reach the surface of the ground or come 

 up much more slowly than the healthy plants. The diseased 

 stems show brownish patches or areas of varying size, situated 

 anywhere on the parts below the surface of the soil. These 

 lesions start at the surface, are not so black as those produced 

 by blackleg, and do not invariably start from the base and 

 work upward as is the case with the latter disease. Badly 

 affected plants are either cut off and killed or have a stunted 

 appearance, frequently showing leaf-roll or rosette characteris- 

 tics. Sometimes a stalk will be cut off" and then throw out 

 new branches from below. 



Fields attacked with Rhizoctonia are quite sure to prove 

 deceptive in the matter of yields. While the plants may be 

 considerably affected by the fungus the majority will appear 

 strong and thrifty till a few weeks before normal maturity. 

 Then, especially if a period oif dry weather comes on, they will 

 suddenly wither and die. When the crop is dug the yield falls 

 far short of what it should be and consists of an abnormally 

 large number of small tubers, many of them not much bigger 

 than marbles — hence the name "Little potato disease." The 

 little potatoes result from the fungus cutting off the tuber- 

 bearing stolons as fast or nearly as fast as they are produced. 



POTATO SCAB. 



The work upon potato scab which has been going on for 

 several years has been continued. Much of that which has 

 been done during the past year has been along the line of 

 laboratory studies of the organism which causes the disease, 

 which while important and necessary are not of general inter- 

 est except where the facts discovered admit of practical appli- 

 cation. 



Comparative studies of a large number of cultures of organ- 

 isms isolated from scabby tubers checked up by inoculation 

 tests, showed that potato scab obtained from many parts of 

 Maine, from several different states and from Canada and 

 Russia is the result of the attack of the same parasite. This of 

 course refers only to the common type of potato scab. 



