THE PREVENTION OF POTATO SCAB. 87 



toes may be included in the rotation without the danger of a 

 large amount of infection. There is reason to believe that possi- 

 bly the latter can be done in from 3 to 5 years on many soils 

 which are not too strongly alkaline. It is a question which must 

 be settled by the individual grower on his own land. However, 

 if one has a piece of badly infested soil the chances of success 

 are sufficient so that it is well worth while to select fertilizers 

 which do not tend to increase scab, to practice rotation with 

 cats, grass, clover, etc., and to frequently plow under a green 

 crop such as clover, rye or buckwheat. 



MANAGEMENT OE CLEAN SOILS. 



On clean soils we are not so restricted with regard to the 

 nature of the fertilizers, except that the manure of animals 

 which have been fed on uncooked scabby potatoes or in which 

 the uncooked refuse or skins have been thrown, should not be 

 applied. 



There is some difference of opinion on the question of the 

 ability of the scab fungus to pass through the digestive tract 

 of animals without being destroyed. Be this as it may there is 

 practically a certainty that the litter from the mangers and some 

 pieces of unconsumed tubers bearing the spores of the fungus 

 will find their way into the manure, and thus make it a con- 

 stant source of danger. 



For seed select tubers which are free from scab and disin- 

 fect by one of the methods described below. While very 

 satisfactory results have been obtained in the disinfection of 

 badly scabbed potatoes no method has been devised which will 

 guarantee an absolutely clean crop from scabby seed. Un- 

 treated, healthy tubers having been in contact with diseased 

 tubers are almost sure to carry sufficient scab germs to infect the 

 soil. 



Bags, baskets, barrels, etc., which have been used for scabby 

 potatoes should not be used for clean or disinfected seed tubers 

 without first being disinfected with formaldehyde gas or solu- 

 tion. 



Plows, harrows, planters, cultivators and other implements 

 should be thoroughly cleaned of all particles of dirt, etc., prefer- 

 ably with a stream of water from a garden hose, when changing 

 to clean from infected tubers or land. 



