Aug. 21, 1916 Control of Powdery Dryrot of Potatoes 831 



surface, no decay occurred. The lime and sulphur dust did not always 

 reach the deeper bruises and therefore was not effective in such cases. 

 Disinfecting potatoes with mercuric chlorid or formaldehyde prior to 

 storage should be of value when it is necessary to store seed potatoes in 

 a poorly ventilated or improperly cooled storage cellar. Lime and sulphur 

 are not recommended. 



SUMMARY 



(1) Powdery dryrot, caused by Fusarium trichoihecioides , is the most 

 important storage-rot affecting potatoes in the irrigated West. 



(2) F. trichoihecioides under ordinary western field conditions does 

 not attack any part of the growing potato plant. Potatoes in storage 

 are attacked only through bruises. 



(3) Planting badly infected seed potatoes greatly reduces the stand. 

 A slight amount of infection in the seed piece does not cause any serious 

 loss. 



(4) The causal organism is at the present time apparently well dis- 

 tributed throughout western desert soils. 



(5) F. trichoihecioides does not develop at a temperature below 2 C. 

 No loss from powdery dryrot occurs when the storage house is kept at 

 this temperature, or lower. In a dry, well-ventilated storage house losses 

 will be very slight at temperatures from 2° to 4 C. (35 to 40 F.). 



(6) Where it is necessary to store seed potatoes in a poorly ventilated 

 or improperly cooled storage house, the disease may be effectively 

 checked by disinfecting the stock, prior to storage, with a solution of 

 mercuric chlorid or formaldehyde, provided the disinfecting is done im- 

 mediately, or within 24 hours after digging. 



