1722 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



ilar to that produced by the common dry 

 rot associated with the late blight fungus. 

 This sirr^ilarity to the late blight dry rot 

 is greatly increased if the spots of pow- 

 dery scab are numerous and close to- 

 gether, so that the discolored area of the 

 skin becomes continuous. 



"In such cases the tissues dry out and 

 shrink away very rapidly beneath the 

 discolored area, giving every appearance 

 of a form of dry rot. Cutting through 

 these blackened areas of the surface 

 usually reveals simply a thin layer of 

 dry, dead tissue resting on the appar- 

 ently sound and healthy flesh of the 

 tuber below. Frequently a distinct strat- 

 um of dry rot has been found beneath 

 some of these discolored areas, but 

 whether or not this is due simply to sec- 

 ondary infection by some fungus I am 

 not yet able to say." 



Thus far no satisfactory method of 

 seed treatment has been devised. When 

 the soil is once infected it requires sev- 

 eral years' rotation of crops to eradicate 

 the organism. 



It is unwise to buy seed potatoes from 

 localities where the disease is known to 

 exist; examine the seed carefully before 

 planting; treat the seed with formalde- 

 hyde or corrosive sublimate even though 

 neither of these treatments is an abso- 

 lute preventive. 



Bhizoctonia, Little Potato 



Gorticium vagum var. solani 

 F. D. Bailey 



This disease is widely distributed in 

 this country and in Europe and Asia. 

 The fungus causing it attacks many other 

 plants, and consequently is an organism 

 having a wide range of destruction. It 

 is often present when very little damage 

 is caused, however, and seems able to 

 live indefinitely in the soil. 



During the season of 1911; this disease 

 has been found on potatoes in the Pacific 

 coast region, and has caused a loss of 30 

 per cent in some cases. 



Symptoms 



The affected plant displays a number 

 of symptoms, some of which accompany 

 the disease only under certain conditions. 



Fig. 1. Rhizoctonia on the Stem of a Young:, 

 Rapidly Growing Potato Plant. 



We often find aerial potatoes produced 

 resulting from early attacks of the fun- 

 gus. This does not always follow, how- 

 ever. Sometimes this production of 

 aerial potatoes is brought about in other 

 ways. It has been observed in a field 

 where gophers had worked around the 

 roots and cut the underground stems of 

 the plants. Many times the tops are 

 large, or an abnormal branching, result- 

 ing in a rosette, accompanies the attack 

 on the underground parts; in this case 

 many small potatoes are produced close 

 to the surface of the ground. Sometimes 

 as many as 50 potatoes, varying from 

 the size of a pea to that of a hen's egg 

 have been found in such hills. 



When conditions are favorable for the 

 fungus to attack the plant early in its 

 growth, death may follow immediately. 

 In such cases the stem rots off at the 

 surface of the ground and the plant falls 

 over. Fig. 1 shows the grayish white 

 fungous growth on the stem just above 

 the surface of the ground. The stem 



