16 CIRCULAR NO. 114, BUREAU OF PLANT INDUSTRY. 



SEED SELECTION. 



It is now the practice among the better growers to select the seed 

 potatoes at digging time for the next year's crop. Others, however, 

 prefer to do it in the winter or in the spring. The best practice is 

 to select seed potatoes in the fall at digging time and then examine 

 them carefully again in the spring when starting the hotbed and 

 discard all that show any symptoms of stem-rot or black-rot. 



It is extremely difficult to tell during the winter or spring without 

 a very careful examination whether a potato is affected with stem- 

 rot. It is comparatively easy, however, to do so in the fall with the 

 vines attached. Before any seed potatoes are selected from a hill, 

 the main stem just above the potatoes should be carefully examined 

 to see that it is not blackened inside and any suspicious hills should 

 be rejected. The selected seed potatoes should be stored in crates or 

 baskets and kept separate from the general stock. Seed potatoes 

 should be disinfected with a corrosive-sublimate solution (formalde- 

 hyde gas or formaldehyde solution should not be used), 1 part of 

 corrosive sublimate to 1,000 parts of water, for about 20 minutes, 

 rinsed in water, and then thoroughly dried. They may be disinfected 

 either in the fall or spring, but preferably in the fall. 



THE HOTBED. 



With clean seed potatoes it is essential that the hotbed should be 

 free from parasitic organisms. Great care should be exercised in 

 the preparation of the hotbed. Before the soil is put in the bed, the 

 cement, boards, or whatever is used in the construction should 

 be thoroughly sprayed with a solution of 5 pounds of copper sul- 

 phate to 50 gallons of water and then with a Bordeaux mixture, or 

 whitewashed. In some localities where these diseases are very preva- 

 lent it is almost impossible to find soil that is not infested. Fields 

 which had not been grown to sweet potatoes for nearly 40 years have 

 given an infected crop when clean slips were used. Where such a 

 general infection has occurred the soil is light and it is probable that 

 the organisms were distributed by the wind. In view of these facts 

 it is advisable to disinfect all hotbed soil. This can be done in two 

 ways: (1) By steam sterilization and (2) by treating with a solution 

 of formaldehyde. 



Steam sterilization is preferable when possible. When disinfecting 

 by steam, any system can be used that insures the greatest efficiency 

 with the least expenditure of time and money. Efficiency, however, 

 should be the first consideration. It is a useless expenditure of time 

 and money to sterilize if it is not done thoroughly or, if after once 

 being thoroughly sterilized, the soil is allowed to become infested by 



[Cir. 114] 



