SILVER SCURF, A DISEASE OF THE POTATO. 21 



Appel as Sporuhjlocladium atrovirens. This is also quite apparent 

 from Bohutinsky's figures. It does not seem very probable that 

 silver scurf is the cause of leaf-roll, but it may well be that it causes 

 abnormal plants in certain instances. The fact that it disfigures the 

 tuber and causes abnormal shrinkage is alone sufficient to involve 

 considerable loss where tubers are to be used for human consump- 

 tion after a considerable period of storage. It is not without destruc- 

 tive effect on the early varieties as well, and especially with red- 

 skinned ones. A shipment has come to the writer's attention in 

 which marked disfiguration occurred in the Bhss Triumph variety 

 grown in the South for the early market. The tubers in some cases 

 were so badly infected that the red color, so characteristic of the 

 sound tuber, was no longer in evidence. In such cases considerable 

 loss occurs, due to the sorting and to the decrease in market value 

 of the infected tubers. 



The big question in connection w^th silver scurf has to do with the 

 effect it wiU have on the tubers used for seed purposes. What 

 will be the effect on the >aeld and general vigor of the crop grown from 

 seed infected mth this disease ? What effect will it have on germi- 

 nation, and will the wounds or lesions due to Spondylocladium increase 

 the susceptibility of the parent tuber to the ravages of wound para- 

 sites? Likewise, the relation of the fungus to the soil and the 

 method of spread of the disease in storage are open questions. These 

 are problems that can not be answered at present, but wliich merit 

 careful consideration, especially where the disease is very prevalent 

 and the tubers are held in poor storage for a considerable length of 



time. 



POSSIBLE METHODS OF CONTROL. 



It is of special interest to know whether tliis disease, confined as it 

 is chiefly to the periderm, can be controlled by the well-known formalin 

 treatment used for the Oospora scab. It is claimed by Johnson that 

 such is the case. He treated tubers for one hour in an 0.8 per cent 

 formahn solution (about 2 pints to 30 gallons of water) and planted 

 the same. Other diseased tubers not treated were planted as checks. 

 When the pota^toes were harvested in the fall it was found that the 

 treated tubers were free from disease, while those from the checks 

 were infected with the brown-mold stage of Spondylocladium, indi- 

 cating that the 0.8 per cent formahn solution either killed or materially 

 inhibited the growth of the fungus. 



The effect of the formahn and corrosive-sublimate treatment as a 

 means of destroying silver scurf has also been tested in the laboratory 

 of Cotton and Truck Disease and Sugar-Plant Investigations. Two 

 varieties of potatoes, the Irish Cobbler and the Green Mountain, 

 were washed and soaked in formahn or corrosive sublimate. Follow- 



[Cir. 127] 



