284 MA1X1-: AGRIClT/rURAL EXl'KRnr ENT STATION. I906. 



once introduced into land, no practical way has thus far been 

 found of removing- it. How long it will remain in the soil is 

 unknown. It certainly may continue for many years even when 

 no potatoes are grown upon the field. 



There are many ways in which it is possible for soil to 

 become affected. The germs may be introduced into the 

 manure pile by feeding scabby potatoes to stock, or by putting 

 them directly into the compost heap. The fungus may then 

 propagate itself in the manure and if this is applied to the 

 land, the disease may be widely disseminated. Alkaline soil 

 favors the growth of the fungus and on this account neither 

 ashes nor lime should ordinarily be used in connection with 

 potato growing. As farm manures are slightly alkaline, they 

 are best not used on potato land. The plowing under of a 

 green crop tends by its fermentation to make the soil slightly 

 acid. This condition is unfavorable to the growth of the 

 fungus. There is a more or less common belief that salt is 

 something of a preventive of potato scab, but exact experiments 

 have failed to demonstrate this. 



Probably the most common way in which scab fungus is 

 disseminated is by the use of infected seed. It is therefore of 

 the utmost importance to use clean seed. Where it is imprac- 

 ticable to procure clean seed, or in case of doubt, it should be 

 treated with a fungicide. While such treatment will help 

 scabby seed, it may not act as an entire preventive. It is there- 

 fore best not to use seed that is much affected. 



Formaldehyde gas either in solution or in the dry gaseous 

 state can be effectively used to clean suspected seed. Formal- 

 dehyde (formalin) is sold in a solution of about 40 per cent, 

 strength and can be obtained at any drug store. A few bushels 

 of seed are most conveniently treated as follows : * Make up a 

 solution of formalin of the desired bulk, using 16 ounces of 

 formalin (40 per cent, solution of formaldehyde gas) to each 

 30 gallons of water. Soak the seed two hours in this solution 

 and then spread out the tubers to dry. After drying, the pota- 

 toes should be cut and planted in the usual way, but care should 

 be taken not to allow them to touch any box, bag or bin where 

 scabby potatoes have been kept. 



The Vermont Experiment Station is studying the treatment 

 of potatoes by formaldehyde gas, and while they have not 



