14 CIRCULAR NO. 110, BUREAU OF PLANT INDUSTRY. 



The disease is still too new and our experience too limited to permit 

 positive statements relative to means of control, but the following 

 advice is based on what is known of the life history of the causal 

 fungus. 



POSSIBLE MEANS OF CONTROL. 



Clean seed. — The powdery dry-rot is a storage trouble and appears 

 not to begin work till after the harvest, yet there is evidence that 

 land becomes infected through planting diseased seed potatoes and 

 that this contagion is carried over until fall and communicated to the 

 new crop. Consequently the most rigid inspection of the seed planted 

 is advised. No potatoes with a trace of decay should go into the 

 ground. All the seed stock should be disinfected by soaking for two 

 hours in a solution of 1 pint of formaldehyde in 30 gallons of water. 

 This will also kill the germs of potato scab. 



Rotation of crops. — Rotation is necessary for the permanent success 

 of potato culture in any country, and particularly in irrigated dis- 

 tricts. While it is possible to produce two or three successive crops 

 on new land, it is unwise to attempt it on account of the disease factor. 

 One potato crop in three years has been proved too short a rotation in 

 many districts. One in five may serve the purpose in our Western 

 States. If a field has produced potatoes affected by powdery dry-rot, 

 it is especially desirable to rotate before planting potatoes there 

 again. 



The storage problem. — Most important of all for the control of dry- 

 rot is the method of handling the potatoes after digging and during 

 storage, as it is probably here that the main fault lies. 



Well-built storage cellars are a necessity from an economic stand- 

 point, to enable the grower to await better prices and to properly 

 assort and pack his crop. In such cellars, if properly built, venti- 

 lated, and wtached, the greatest immunity from decuy may be 

 insured. 



These storage houses should be thoroughly cleaned at the end of 

 the season, all old potatoes and debris carried out, and the walls and 

 floors washed with a disinfectant like copper sulphate (blue vitriol), 

 using a 1 per cent solution, or corrosive sublimate, using 2 ounces to 

 16 gallons of water. 



The greatest losses that have been brought to our attention have 

 occurred in that portion of the crop which was not put in storage or 

 shipped direct from the field to the market, but held for some weeks 

 after having been dug and sacked. Such potatoes, stored in sacks 

 in large piles and subjected to variable and occasionally rather high 

 temperatures, offer most favorable conditions for the development 

 of the dry-rot fungus. 

 [Cir. 110] 



