EXPERIMENT STATION BULDEtlNS. 347 



TREAT SEED IN THE FOLLOWING MANNER. 



Soak the seed tubers in corrosive sublimate solution for one-half hour. 

 The solution is made with four ounces of corrosive sublimate in 30 gallons 

 of water. This treatment controls Scab and Black Scurf. Reinfection from 

 untreated sacks must be avoided. Disinfect these containers in the treat- 

 ing solution. 



POINTS ON THE TREATMENT. 



Corrosive sublimate crystals or the diluted solution are deadly poisonous. 



Use precaution and keep this material out of the way of live stock or children. 



The crystals dissolve slowly in cold water, but rapidly^in hot water. 



Treated tubers are not safe to feed to stock. 



Corrosive sublimate, as the name indicates, attacks metals. It must be 

 used in wooden vessels. 



Potatoes should be uncut when soaked. 



Treatment with small lots can be readily given by use of a barrel, soaking 

 one sack at a time. 



Larger quantities can most readily be handled in a large vat made of heavy 

 stuff, holding 8 to 12 crates at a time. It is well to make this vat water- 

 tight by the use of heavy duck lining, painted with some water-proof paint, 

 such as asphaltum. 



The solution can be used four times. It loses strength, due to the potatoes 

 taking out more of the chemical than they do of the water. After the fourth 

 batch is treated, make up fresh. 



The addition of one ounce of corrosive sublimate to 30 gallons of solution 

 after each batch is dipped, keeps the treating solution at the proper strength. 



Experiments completed since 1917, at the Michigan Agricultural College, 

 show that treatment for one-half hour is as efficient as the longer soaking 

 (13^ to 2 hours), previously advised. 



i SCAB. 



An interesting fact was gleaned from the seed treatment experiments of 

 1919 and 1920, in relation to Scab control in the limestone regions of the 

 Upper Peninsula. Although corrosive sublimate was found to be effective 

 for Rhizoctonia and Blackleg, neither this disinfectant not formaldehyde 

 were found to control Scab. Plats planted with clean seed which had been 

 treated with corrosive sublimate showed as much Scab as plats planted with 

 scabby seed which had not been treated. These plats were planted on virgin 

 soil of limestone formation, which had never borne a previous crop of potatoes. 

 High percentages of Scab were found in all plats regardless of previous treat- 

 ment. This would indicate that the Scab organism must be present in the 

 virgin calcareous soils of the Upper Peninsula, and that seed treatment for 

 Scab control is not effective in such areas. 



Knowing that the scab organism requires a sweet or alkaline soil for growth 

 and is not present in acid soils, some experiments were conducted in 1920 to 

 change the soil reaction so that it would become more acid or sour, and thus 

 discourage the growth of the Scab organism. Sulphur was used in these 

 trials and was applied at planting time. At harvest the yields from these 

 plats did not show any appreciable decrease in the percentage of Scab, but 

 soil samples taken shortly before harvest showed that the soil reaction had 

 changed sufficiently to prohibit the growth of the Scab germ. It is probable 



