276 ARID AGRICULTURE. 



losses. This disease is due to a fungus known 

 as Rhyzoctonia. It appears in various forms, 

 and receives different names, according to the 

 way it strikes. Common names for it are "Root 

 Rot/' "Little Potatoes/ 7 "Big Vines and Little 

 Potatoes/ 7 "Collar Rot/ 7 and "Blight/' and Pro- 

 fessor Paddock informs me it is the cause of 

 most of the Western potato scab. This fungus 

 lives through the winter, either in the soil or in 

 the resting stage (sclerotia) on the potatoes 

 themselves. The disease can be recognized 

 by anyone who knows what to look for. It 

 appears as spots of brown or black on the outside 

 of the potato. These spots may be from the size 

 of a pin point to a quarter inch in diameter, and 

 they stick very tight to the potato skin. They 

 look like particles of black soil. Seed potatoes 

 with much of this disease on them should not be 

 planted, or if they must be planted, they should 

 be sunburned, as suggested in our chapter on 

 potatoes. The principle remedy for this dis- 

 ease, as stated by Professors Paddock and Ben- 

 nett, is to plant on "potato soil. 77 They class as 

 potato soil those loams which are well under- 

 drained, or alfalfa sod upon which experience 

 shows that potatoes will grow. There are cer- 

 tain regions in the West where potato culture 

 fails on account of Rhyzoctonia, and with our 

 present knowledge such areas can not be made to 

 produce sure and heavy crops of potatoes. 



