Aug. 21, 1916 Control of Powdery Dryrot of Potatoes 827 



and poorly ventilated. He has been in other cellars where the bruised 

 tubers showed only an incipient rot, the decay usually extending inward 

 from the bruised surface for less than one-fourth of an inch. Such cellars 

 have invariably been very dry and well ventilated. It is to be regretted 

 that there has been no opportune to obtain the percentages of atmos- 

 pheric humidity most favorable to the development of the rot. How- 

 ever, a preliminary study of the effect of humidity on powdery dryrot 

 development was undertaken in the spring of 191 5. 



In the month of April, owing to the fact that heavy rains had been 

 falling, the storage cellar of the Jerome Experiment Station was in a com- 

 paratively damp condition, the doors having been open for a considerable 

 portion of the time to allow workmen to enter. At the same time the 

 cellar under the Station laboratory building was being kept in a compara- 

 tively dry condition, while the air of the laboratory itself was very dry, 

 owing to the fact that fire was being constantly maintained in the stove. 

 One hundred and fifty Netted Gem tubers inoculated with F. trichothe- 

 cioides were allowed to remain for several days in moist chambers until 

 the fungus had well established itself, after which fifty tubers were re- 

 moved to the potato storage cellar; fifty of the tubers were put in the cellar 

 of the laboratory building, while the remaining fifty tubers were exposed 

 to the dry air of the laboratory room. After six weeks the potatoes were 

 examined. Though the temperature had been very favorable for the 

 development of the rot, the fifty tubers left in the dry laboratory room 

 showed no apparent advance in the decay from the time they had been 

 removed from the moist chambers. Those in the laboratory cellar showed 

 but a very slight advance in the decay, while those in the storage cellar 

 showed well-defined pockets of dryrot, each tuber being from one-eighth 

 to one-fourth decayed. This preliminary experiment shows that the 

 drier the atmosphere the less will be the decay in storage from this cause. 



DISINFECTION OF POTATO STOCK BEFORE STORING 



In order to learn whether the progress of powdery dryrot in storage 

 could be inhibited by disinfecting the potatoes before storage, the follow- 

 ing experiments were set up. Both bruised and sound tubers were em- 

 ployed. The bruised ones had been injured in the field during the 

 process of digging. Fumigation with formaldehyde gas was the method 

 of disinfection used. The potatoes were fumigated in an air-tight room 

 at a temperature of about 6o° F. To produce the formaldehyde fumes 

 the following formula was employed: Formaldehyde (40 per cent), 3 

 pints; potassium permanganate, 23 ounces for each 1,000 cubic feet of 

 space. The potatoes were arranged in two lots as follows : 



Lot 1 in trays, each tray holding about 50 pounds of potatoes. One 

 tray each of bruised tubers of Early Rose, Improved Peachblow, Peoples, 

 Netted Gem, and Pearl, and three trays of bruised tubers of Idaho Rural; 

 also a similar number of trays of sound tubers of each variety. 



