214 The Potato 



damage even though the seed has been, carefully selected 

 and treated and other precautions taken. 



Treatment for potato blight 



The blight-rot fungus is not destroyed by seed treat- 

 ment, and slightly affected tubers may be overlooked in 

 sorting. Blight spores, being easily carried by air cur- 

 rents, are readily disseminated from one field to another 

 and bring about an infection if wet weather prevails. It 

 must be remembered that the tubers are infected by 

 spores produced on blighting vines. Hence, to prevent 

 this rot from occurring, it is necessary only to prevent 

 the vines from blighting. The vines will not blight, even 

 under very favorable weather conditions, if the spores do 

 not gain entrance into their tissues. The spores cannot 

 enter the leaves if the vines are thoroughly sprayed with 

 bordeaux mixture before the spores have germinated. 

 As they germinate only in the presence of moisture, the 

 applications need be made only before moist conditions 

 prevail, that is, before rainy periods. "The grower should 

 not hesitate to spray at such times for fear that the mix- 

 ture will be washed off. It dries rapidly, and once dried 

 on the vines, enough remains even after heavy rains to 

 protect them from the fungus." 



Every susceptible part of the vines should be protected 

 by the mixture. To do this effectively, it is necessary 

 that the mixture should come from the nozzle as a fine 

 mist and settle over every leaf and stem like a fog. Such 

 a mist can be produced with a satisfactory nozzle and 

 with good pressure. 



One application thoroughly done will protect the parts 

 receiving it for a long time, but new leaves appear, and 



