1921.] 



Corky Scab in Potatoes. 



1D79 



Owing to the severe attacks of Corky Scab in certain districts, more 

 particularly in Derbyshire and Lancashire, the Ministry started a series of 

 small experiments with a view to testing the resistance of different varieties. 



It was known that some of the varieties immune to Wart Disease were 

 particularly susceptible to* Corky Scab, and unfortunately many of the gardens 

 which were infected already with Wart Disease and where only immune 

 varieties could be grown, proved to lie infected with Corky Scab as well. 

 Hence in the first place only varieties immune to Wart Disease were tested, 

 although in one case " Sharpe's Express " was also tried. 



Trials were undertaken at two Centres, namely, two adjoining garden plots 

 in Derbyshire, near Stockport, and another garden plot at Gisburn, near 

 Clitheroe in the West Riding. It was known that the soil in the Derbyshire 

 plots was infected with Corky Scab, but less information was available 

 concerning the Gisburn soil, although it was ascertained that the disease had 

 been present there in former years. 



In Derbyshire, where the Trials were carried out by officers of the Derbyshire 

 Agricultural Education Sub-Committee, the following varieties were planted 

 and the percentage attacked by the disease is given : "Great Scot" (100 per 

 cent.); "Golden Wonder" (98 per cent.); "Flourball" (98 per cent.) : 

 " Arran Comrade " (95 per cent.) ; " King George " (80 per cent). 



On another plot in the vicinity, only "Great Scot" and "Templar" were 

 grown, with the result that 95 per cent, of "Great Scot" were attacked but 

 the severity of the disease was less, and 60 per cent, of " Templar" were 

 attacked. 



At Gisburn no variety was severely attacked owing probably to the slight 

 infection present in the soil. On the other hand the intensity and percentage 

 of attack varied, as is shown by the following table : — 



Variety. Percentage of diseased Tubers. 



Intensity. 



Edzell Blue 



30 



Severe 



Great Scot 



10 to 12 



General 



Majestic 



10 



General 



Bishop 



10 



Slight 



Dargill Early 



10 



Slight 



Sharpe's Express 



9 . 



Slight 



Lochar 



9 



Slight 



Golden Wonder 



8 



Slight 



Arran Eose 



8 



General 



Kerr's Pink 



6 



Very Slight 



Tinwald Perfection 



6 



Slight 



King George 



6 



Slight 



Ally 



5 



General 



Templar 



4 



Very Slight 



Note. — The Edzel Blue were in a low-lying part of the garden. 



While no variety of potato appears to possess immunity from Corky Scab, 

 some varieties have more resistance than others. 



In every instance the soil, where the potatoes were grown, was heavy and 

 had a tendency to hold water. The experience of the Ministry with similar 

 cases of this disease shows that it is always more severe where the soil is damp 

 or water-logged. The natural, and probably the most efficient remedy in 

 dealing with soils producing potatoes attacked by Corky Scab lies in proper 

 and efficient drainage. 



