212 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



beneath. The fifth inoculated puncture developed no decay. 

 These and the other inoculated tubers were later placed in a 

 moist chamber but no more injury developed. No decay or 

 discoloration appeared on the check punctures or where the 

 fungus was placed on the surfaces over lenticels. 



We have, therefore, been unable to present any conclusive 

 evidence that Rhizoctonia produces a true decay of stored or 

 growing potatoes. However, on the latter in the soil after the 

 tubers had been cut ofif from the parent stem a distinct necrosis 

 of the surface which works slowly inward, o'ten producing 

 deep cavities in the basal end is by no means uncommon in 

 severe attacks of the disease. 



Experiments with germicides and disinfectants. Field experi- 

 ments with germicides and disinfectants both upon soil and seed 

 are now under way. The present discussion will, however, be 

 confined to certain rather limited greenhouse experiments. A 

 review of the previous work on formaldehyde and corrosive sub- 

 limate as a means of disinfecting seed tubers for Rhizoctonia 

 has already been given and it has been shown that data obtained 

 to date indicate that corrosive sublimate is the more effective 

 of the two. Our own experience in using sterilized soil in the 

 greenhouse indicates that formaldehyde is of some value but 

 even under the best of conditions was not always effective. 



In one lot of 40 ten-inch pots of soil sterilized for two hours 

 at 20 pounds steam pressure, planted with formaldehyde disin- 

 fected potatoes which had been first thoroughly washed and a 

 large percentage of the sclerotia removed, the crop produced 

 in two of these pots showed Rhizoctonia sclerotia on their sur- 

 faces. In another case out of 25 pots one plant developed the 

 Corticium stage of the fungus on the stem. 



Six tubers badly covered with sclerotia were selected and 

 planted in sterilized soil after first disinfecting 3 of them with 

 formaldehyde in the usual manner. In both lots bad cases of 

 the disease developed. The yield consisted exclusively of little 

 potatoes, close to the surface and covered with sclerotia. One 

 plant from each lot of disinfected and undisinfected tubers 

 showed typical stem lesions below ground and one plant from 

 each series produced the Corticium or fruiting stage above 

 ground. 



In another trial formaldehyde was much more effective. In 

 this test 6 tubers badly covered with the sclerotia and 6 badly 



