326 MAiNi: AGRicuivTURAiv e;xpe;rime;nt station. 1909. 



going into the room it may cause some irretation of the mucous 

 membranes of the nose and throat but this soon passes away. 

 It should be mentioned that the amounts of formaldehyde 

 here recommended and the length of exposure to the gas are 

 far in excess of that found necessary for disinfecting rooms 

 for contagious diseases, and are doubtless considerably greater 

 than are needed for treating seed tubers. However, experi- 

 ments have shown that the large amount of gas and long expos- 

 ure, if done according to directions here given, will not injure 

 the germinating quality of the tubers and will control the scab 

 fungus as well, therefore, it seems best to advise a treatment 

 which will answer for both diseases at the same time. If it is 

 desired to reduce the amount of solution and the time of expos- 

 ure the writer would not advise going below 2 pints of formal- 

 dehyde solution and a proportionate amount of potassium 

 permanganate for each 1000 cubic feet of space and 12 hours 

 for the lower limit of exposure. 



, Whether or not the disease germs can remain in the soil for 

 any length of time to infect later crops is still an open ques- 

 tion. The fact that field observations show that the disease, 

 as has already been stated, is almost invariably confined to 

 scattered hills and to stalks which spring from decayed seed 

 pieces indicates that most or if not all the infection comes from 

 diseased seed. However, the somewhat closely related organ- 

 isms which are associated with the soft rots of cabbage, cauli- 

 flower, etc., apparently remain alive in the soil for some time 

 at least. There is no reason why the blackleg organism should 

 not do the same. Therefore, land upon which a potato crop 

 has been grown which was attacked by this disease should be 

 kept in other crops, preferably grass, clover or cereals, for as 

 long as possible before again using it for potatoes. The prac- 

 tice of growing two crops of potatoes on the same land in suc- 

 cessive years should be discouraged, and low, poorly drained 

 soils should be avoided. Fields which show scattered affected 

 stalks should be frequently inspected during the growing sea- 

 son and all diseased plants and any tubers which may have 

 formed on them dug up and burned. Under no condition 

 should the crop from badly or even moderately afifected fields 

 be used for planting in Maine or shipped South for seed. Sev- 

 eral of the leading: seed dealers in Maine are doing their best 



