92 MAINE AGRICULTURAL EXPERIMENT STATION. igOJ . 



SUMMARY. 



The use of untreated seed and the too common practice of 

 reserving unsalable, scabby tubers for planting has resulted 

 recently in a rapid increase of potato scab in Maine. Page 81. 



Scab is caused by a minute parasitic fungus. Soil conditions, 

 the application of lime, ashes, chip dirt, etc., may favor the 

 development of scab but are incapable of causing it. Page 83. 



Crop infection on old land may come from the soil, from the 

 seed, or from both. On new land the source is largely from 

 undisinfected seed. Page 84. 



Alkaline soils, the use of stable manure, lime, ashes, and cer- 

 tain chemicals of an alkaline nature favor the fungus. Acid 

 soils and certain other chemicals are unfavorable to it. Page 84. 



Beets and the roots of a few other vegetables are attacked by 

 the disease but the fungus may persist in infected soil for sev- 

 eral years without the presence of known host plants. Pages 

 82 and 86. 



Badly infested soils should be devoted to such crops as grains, 

 grasses and clovers, for as long a time as possible. Fertilizers 

 favorable to scab should be avoided and "souring" the soil by 

 green manuring is recommended. Page 86. , 



On clean soils, only healthy, disinfected seed tubers should 

 be used. Manure containing uncooked scabby potatoes or 

 refuse should be avoided but no other precautions as to fertili- 

 zers are necessary. Clean soil may be infected by means of 

 tools, bags, baskets, etc., which have been in contact with 

 infected land or tubers. Page 87. 



Small amounts of seed are best disinfected by soaking: (a) 

 2 hours in solution of one-half pint formalin to 15 gallons water, 

 or (b) one and one-half hours in 2 ounces of corrosive subli- 

 mate dissolved in 15 gallons of water. Page 88. 



For large quantities of seed, formaldehyde gas, generated by 

 the use of potassium permanganate, is the most practical disin- 

 fecting agent. Place seed tubers in bushel crates or shallow, 

 slat-work bins in a tight room. For each 1,000 cubic feet of 

 space spread 23 ounces of potassium permanganate evenly over 

 the bottom of a large pan or pail in center of room. Pour over 

 this 3 pints of formalin, leave room at once and allow to remain 

 tightly closed for 24 to 48 hours. Page 89-91. 



