SPECIAL REPORT FOR YEAR. 55 



LaboTatory experiments showed that the common potato 

 scab organism is extremely susceptible to the effects of direct 

 sunlight. Fifteen minutes exposure was sufficient to kill all of 

 the germs of the disease when spread out in a thin layer in a 

 culture dish. This explains why sunning potato seed for 

 several days before planting tends to reduce the amount of 

 scab on the crop. It was also determined that the organism is 

 very readily killed by drying and that it is destroyed by much 

 weaker dilutions of formaldehyde and corrosive sublimate than 

 are usually employed for disinfecting purposes. However these 

 stronger solutions are necessary for disinfection on account of 

 the fact that the scab organism is fairly well protected by the 

 corky tissues covering the diseased spot. 



In an experiment to test how long potato scab would remain 

 alive in the soil without the presence o>i any crop, the details 

 of which it is not necessary to give here, it has been found that 

 the organisms causing the disease were able to persist in the 

 soil kept entirely free from vegetation and outside contamina- 

 tion for at least 3 years. This work will be continued for sev- 

 eral years. A part of the same experiment has also to do with 

 the question of what effect growing various grains, grasses 

 and clovers on scab infected ground has upon the continuance 

 of the germs in the soil. 



A TWO-WHEEEED POWER SPRAYER EOR POTATOES. 



The ideal potato sprayer is one which will cover all parts of 

 each and every potato hill thoroughly. This means that by the 

 use of such a sprayer the lower leaves and the under sides of 

 all leaves are as well coated and protected from fungous attacks 

 as the upper sides of the outer leaves of the hill. Bordeaux 

 mixture is a preventative and not a cure and it must be on the 

 leaves before the spores of the parasitic fungus 'which causes 

 the blight. Any application of a spray which only partially 

 or slightly meets these requirements must not be expected to 

 give complete protection from disease. 



One nozzle to the row and 50 gallons of bordeaux mixture 

 to the acre should never be expected to give complete protec- 

 tion, and should never be used except when the plants are small. 

 As the plants increase in size the number of nozzles should be 



