260 MINNESOTA STATE HORTICULTURAL SOCIETY. 



on new land. There are occasional exceptions to this rule, but they 

 do not occur very often. (2) That in old potato around, i. e., where 

 the scab has been harmful, the crop is almost certain to be scabb)', 

 even though perfectly clean, healthj^ seed is planted. 



The Length of Time the Germs of Scab will Live in the Soil 

 is not known, but the experience of various growers would seem to 

 show that they maj^ live at least three or four years, and Prof. Bailej' 

 states it has been known to have seriousl}' injured a crop of beets 

 after an interval of live j^ears from the time when a crop of scabby 

 potatoes was harvested. In this connection.it is of interest to know 

 that the disease called scab on beets is the same as scab on pota- 

 toes, and, consequently, potatoes should never follow a crop of 

 scabbj' beets without an interval of at least six years, which maybe 

 long enough to permit the germs to die out in the soil; but as this 

 time may not be long enough to thoroughly cleanse the land from 

 the germs of the scab fungus, a longer time should be allowed to 

 intervene whenever it is practicable. 



Importance of clean seed.— The importance of having seed po- 

 tatoes perfectly smooth and free from scab or contamination bj- 

 coming in contact with diseased potatoes cannot be too firmlj- in- 

 sisted on. It is not enough to have the seed smooth and clean as it 

 would be were it freed from rough or injured tubers that showed 

 signs of the disease, but if the clean seed potatoes have been in con- 

 tact with those that are scabby the chances are that some germs 

 of the disease will adhere to them and be read}- to grow as soon as 

 a favorable opportunit}' otfers. Where there is the least suspicion 

 that clean seed potatoes are infected, or when one is using- seed the 

 history of which is not known, the chances of injurj^ from this 

 source will be greatlj^ lessened, if not entirelj' eliminated, by thor- 

 oughly washing the tubers in running water before planting. This 

 may be done by placing a trough where water will run through it; 

 into this pour one layer of potatoes at a time and rub them with a 

 broom or brush until thej- appear clean and bright, even in the eyes. 

 This will probablj^ remove the germs that adhere to the skins. If 

 such potatoes are planted on perfectly clean land, there is no doubt 

 but what the crop from them will be smooth, although, even if 

 grown from such seed potatoes, some germs niaj' remain after the 

 rubbing process, and the little scab thus spread ma}- gradtially 

 increase until it becomes a source of trouble; so that, even where this 

 method is adopted, it will be found a good plan to occasional]}- 

 change the land used. A better plan would be to disinfect with 

 corrosive sublimate as recommended for scabby seed. 



Scabby seed potatoes may be safely planted, provided the}- are 

 first treated with some material that will kill the germs of the seal' 

 fungus on the skin. Many experiments have been made in this liiu- 

 with various fungicides. The most uniformly successful results 

 have come from soaking seed potatoes before planting- in a solution 

 of mercuric bichloride. Prof. Bolley, of North Dakota, who has exper. 

 imented very largely with this treatment and achieved remarkabU- 

 success in its use, recommends the following method: "Procure an 

 ordinary barrel and fit into the base a common wooden faucet. Pur- 



