8o 



years in the given district, and by choosing early varieties 

 it is possible to avoid this disease to some extent. 



It IS even more important, however, to endeavour to 

 prevent the f±rst outbreak of the disease in a given area. 

 All possible sources of infection such as diseased tubers 

 and stalks should be carefully collected and burned at 

 the end of the season. Since the disease is propagated 

 from year to year in slightly diseased tubers, seed potatoes 

 should only be used from a crop which never showed 

 any sign of the disease even on the leaves. 



We have seen that tubers become mfected either, by 

 the growth of fungus down the stalks, or by spores being 

 washed into the soil. If, therefore, the attack occurs late 

 in the season all haulms should be removed and destroyed 

 before the tubers are lifted; and infection from the latter 

 source may be prevented, to some extent, by seeing that 

 the tubers near the surface are well covered with soil. 

 This should be done as soon as possible after the haulm 

 has died down, for apart from the risks of the Phyto-ph- 

 thora disease, tubers left too long in the ground are 

 more liable to be attacked later by rots in the store. 

 The tubers should be stored under dry conditions in such 

 a way that air has free access to them, and diseased 

 haulms should never be used for covering the '^pie" or 

 clamp. 



If potato plants are sprayed three or four times at 

 fortnightly intervals, beginning when they are about six 

 inches high, it should usually be possible to prevent any 

 serious epidemic in a given field or garden. Much can 

 also be done to prevent infection by the immediate destruc- 

 tion of diseased tubers and haulms, and by only using 

 seed potatoes from a perfectly healthy crop. By such 

 precautionary measures, in addition to the use of varieties, 

 known by experience to be resistant in the district, it 

 should be possible to reduce the effects of this disease to 

 a minimum. 



