Rural School Leaflet 



923 



also killed the eyes, or undeveloped sprouts, of the potato. A treatment 

 with hot air has been recommended, but this is not convenient for most 

 farmers. Certainly, diseased tubers should not be planted. One should 

 obtain seed tubers from fields that were free from the disease, or should 

 carefully sort out and discard all tubers showing any rot. Even then, some 

 of the fungus may slip through and the disease in the field start from this. 

 If one were perfectly sure that all tubers planted by him were free from 

 this disease and that there were no neighboring fields within a half mile 

 from which the spores of this fungus could be carried, he need not fear 

 that the disease .would develop in the vines of his potatoes ; but since one 

 cannot be sure of these conditions, it is wise to protect all the vines from 

 infection. This can be done successfully by spraying them thoroughly 

 with bordeaux mixttue several times diiring the season. This mixture 

 dries on the vines and is not washed off easily by rains. When the ger- 

 minating swarm spore secretes the enzyme that dissolves the cuticle of the 

 leaf, some of the copper in the bordeaux mixture, if present, is released 

 from its combination with the lime and, penetrating the young infection 

 tube, destroys it before it has been able to enter the leaf. In order, there- 

 fore, to protect all parts of the vine it is necessary to have all parts covered 

 by the mixture. The potato vine grows throughout the summer and the 

 new growth made after one spraying should also be protected by a second 

 appHcation, and so on throughout t.he summer. 



A field of potatoes of which one row that was not sprayed was entirely killed by the 



downy mildew 

 (After Geneva Bui. 264, Plate XV) 



