DISEASES OF CULTIVATED PLANTS 669 



Potato Disease and Treatment of Seed. There can be no 

 doubt that the success of the potato crop depends very much on 

 the condition of the seed. Our experiments indicate that treatment 

 of the seed, if it be carefully done, will prove highly profitable. The 

 average grower does not realize as great profit from his potatoes as 

 he might. There are too many failures ; too many instances of only 

 partial crops, and top many potatoes put on the market which are 

 scabby or otherwise imperfect. 



About two years ago Prof. F. M. Rolfs of the Colorado Ex- 

 periment Station discovered the cause of many of our potato fail- 

 ures, and his study since that time has been of great value to the 

 potato grower. The troubles which are often called blight, collar 

 or crown rot, black ring, and little potatoes, are due to a disease 

 which is caused by a fungus, known as Rhyzoctonia. This fungus 

 grows on a dozen or more different kinds of plants, and does seri- 

 ous injury to several of our more important agricultural crops. 

 It was first discovered on alfalfa and clover roots in Europe nearly 

 ninety years ago, but the first account of its appearance in this 

 country was published by the Cornell and Geneva Experiment 

 Stations in 1901. So serious is the pest on potatoes in the West, 

 that it not only decreases the potato crop thousands of dollars' 

 worth every year, but over large areas farmers make few attempts 

 to raise potatoes at all, under the impression that their soil is such 

 that it is impossible to grow profitable crops. 



In our potato regions it is necessary to change seed every two 

 or three years, in order to get that which is more free from the 

 disease or more able to resist its attack. Two years ago potato 

 crops failed generally over a large portion of the West. The cause 

 was not apparent, but it is now believed that the season was espe- 

 cially favorable to the growth of this fungus. 



The fungus grows on the potatoes themselves, producing rough, 

 cracked, corky skins, but the principal damage is done by its attack 

 on the young sprouts. It either kills them before they come up, 

 causing poor stands of plants, or affects the growing vine in such a 

 manner that the root-stalks, upon w r hich the young potatoes set, are 

 either cut off or the vine is deprived of nourishment, so the tubers 

 which do set on, remain small. The effect on the vines is often called 

 blight. The fungus remains over winter in the soil, and also on the 

 potatoes themselves, where it is easily seen in the brown or black spots 

 which look like particles of soil, and these are difficult to remove, but 

 when rubbed open they look something like smut of the wheat 

 kernel. 



If potatoes are grown on soil which has become affected with the 

 fungus, little can be done, though Rolfs found that after the vines 

 showed blight, spraying with Bordeaux mixture increased the crop. 

 It is believed that the fungus will live at least three years in the soil, 

 and be ready to produce the disease on potatoes planted therein. 



Dissolve two ounces of corrosive sublimate in two gallons of hot 

 water, and mix this with fourteen gallons of water in a barrel. This 

 gives a solution containing one ounce of corrosive sublimate in eight 



