92 



All affected plants should on the first appearance of the disease be cut 

 down to the ground, to avoid the affection spreading to the tubers, for it 

 must be remembered that when once this bacillus has gained an entry into the 

 tissues of the potato-haulra, spraying would be of no avail. The tops, when 

 cut off. should, if possible, be burned. — tiew Zealand Bulletin, No. 25. 



Potato Scab (Oosporia scaWes). 

 Description. 



At the present day Oosporea scahies is one of the most widespread of 

 diseases affecting the potato. The fungus usually attacks the tubers while 

 young, forming scattered rough patches or scabs on the surface ; these patches 

 gradually increase in size and number, and not infrequently when the tuber 

 Is full-grown its surface is more or less completely covered with scab. 



The injury is confined to the surface of the tuber, the skin being broken 

 up into fragments over the disea.sed patches. Although the market value is 

 much depreciated when scab is present in quantity, the quality of the potato 

 is not in the least impaired for eating. 



rrcvcntion and Remedies. 



(1.) If scalAed potatoes are used for "seed" without having been ster- 

 ilised, the resulting crop will almost certainly be diseased, and in addition the 

 fungus will pass into the soil, where it is capable of living for several years. 

 Scabbed potatoes may be used for "seed" without the slightest danger of 

 spreading the disease if they are immersed for two hours in a solution consist- 

 ing of one pint of commercial formalin (=formaldehyde, 40 per cent.) mixed 

 with thirty-six gallons of water. The potatoes are then spread out to dry. 

 when they may be cut and planted in the usual manner. Great care must be 

 taken after potatoes have been treated as above that they are not placed in 

 sacks or hampers that have contained scabbed potatoes. 



(2.) Land that has produced scabbed potatoes is certain to be infected 

 with fungus, and should not be planted with potatoes for several years after- 

 wards ; beet, swedes, carrots, and cabbages are also attacked by the fungus. 

 Cereals may be sown with safety on infected land. 



(3.) In the case of gardens and small allotments, where potatoes are of 

 necessity grown every year, the trenches in which the potatoes are planted 

 should be sprinkled with powdered sulphur. 



(4.) Lime favours the development of the fungus in the soil: the same 

 is true of stable manure, night-soil, etc. Acid manures only should be applied 

 to land that is infected. 



(5.) Peelings from infected potatoes should not be fed to pigs unless they 

 have been boiled. Burning is the safest, and in the end the most economical, 

 method of dealing with them. — Board of Agrieulture and Fisheries, London, 

 Leaflet No. 137. 



What iriU iirerent Scab on Potatoes? 



There are two more or less standard remedies for the prevention of potato 

 scab: (1.) Soak uncut seed potatoes in a solution of one ounce of corrosive 

 sublimate in eight gallons of water: (2.) Soak cut or uncut potatoes in 

 a solution of one pound of formalin in fifteen gallons of water. These solutions 



