POWDKRY SCAB Of^ POTATOES. lOI 



per cent solution of capper sulphate and soaking the potatoes 

 for 3 hours gave even better results but the copper sulphate 

 produced injuries sufficient to materially reduce the yield. Ber- 

 gundy mixture (copper sulphate and sal soda) was nearly as 

 efficient as formaldehyde but its effect on the crop was similar 

 to the copper suilphate solution alone. Rolling moistened seed 

 tubers in calcium cyanamide destroyed their gerniinating quali- 

 ties. The sam.e treatm.ent with superphosphate destroyed four- 

 f.fths of the seed tubers but gave a clean crop. 



These results coming from a recognized authority on potato 

 diseases are very suggestive as to what may be done along the 

 line of seed disinfection but the fact should not be lost sight 

 of that a perfect score was only obtained at the expense of a 

 largely reduced crop. Also it is doubtful if Dr. Pethybridge 

 himsdlf would care to predict how effective these methods of 

 seed treatment would prove to be under Maine conditions. His 

 results, however, do indicate promising lines of attack upon 

 which to base experimental work in this State. No treatment 

 of this nature should be absolutely relied upon till it has been 

 tried out by a number of investigators, under a variety of con- 

 ditions. 



It will be noted that in his second series of experiments Dr. 

 Pethybridge used a much weaker solution of formaldehyde 

 (i to 600) than is customary to recommend in this country for 

 treating seed potatoes, but soaked for a longer time, 3 hours. 

 This Station has always used and recommended one pint of 

 40 iper 'cent formaldehyde in 30 gallons of water (i to 240) and 

 soaking the potatoes for 2 hours in this. This strength of solu- 

 tion has been found to be very effective in treating for the ordi- 

 nary type of scab and for blackleg. Doubtless it would be more 

 efficient than the weaker solution for a longer period. 



Reasoning apparently on a priori grounds, since liming soils 

 tends to control club root of the cabbage, also caused by a slime 

 mold or myxomycete, led one English writer to recommend this 

 for powdery scab. Pethybridge* has since shown that not only 

 is lime not a soil disinfectant with reference to powdery scab 

 but as is the case with common scab its application to the land 



* Pethybridge, G. H. Jour. Dep. Agr. Tech. Inst. Ireland. 10 : 254-256. 

 1910, 11 : 26-29. 191 1, 12 : 19-22. 1912, 13 : 459-461. 1913. 



