POTATO SCAB 257 



greater part of the external surface of the tuber. 

 The presence of the fungus may be detected by dis- 

 coloured blotches on the skin. It often happens that 

 no trace of the disease is to be seen at the time of 

 harvesting, but it frequently shows itself during 

 winter in stored Potatoes, small discoloured spots first 

 appearing on the skin of the tuber. These spots 

 increase in size and become confluent, till at length 

 the entire surface of the potato is discoloured. The 

 cuticle then bursts in many places, and the olive-green 

 spores are set free. 



Prevention. Scab may generally be prevented by 

 adding lime to the soil, either in the autumn or early 

 in spring, and avoiding the use of rank manure at the 

 time of planting. A hundredweight of quick lime 

 per rod is a proper quantity to apply, slaking in little 

 heaps convenient for spreading, and digging or plough- 

 ing in as soon afterwards as convenient, always choos- 

 ing a dry time for the operation. If manure is applied 

 in autumn the liming may be performed in March. 

 In the case of land previously heavily manured it is 

 well to omit manuring altogether, relying upon the 

 liming and the application of artificial fertilisers. 

 When the land is limed in autumn thoroughly rotted 

 stable or farmyard manure may be applied in spring. 



No Potatoes showing traces of scab should be 

 planted, and when the disease appears among stored 

 tubers the whole should be sorted and the sound ones 

 freely dusted with air-slaked lime before again storing. 

 When Sorosporium disease in the Potatoes is suspected 



17 



