i66 Maine; agricuIvTurai, e;xppi;rime:nt station. 1909. 



ditions,* and at other experiment stations, particularly those 

 obtained at the Vermont and the New York State Station lead 

 to but one conclusion, namely : that from 75 to p§ per cent of 

 the loss from blight and rot even under the severe weather con- 

 ditions experienced during the tzuo growing seasons under con- 

 sideration is unnecessary and unwarranted] In fact there are 

 few plant diseases which are so completely and thoroughly 

 controlled by bordeaux mixture as the late blight of potatoes 

 and the resulting decay of the tuber caused by the same fungus. 

 Granted that the above statement is true, why has there been 

 an apparent almost universal failure from spraying during the 

 season of 1909, and to a somewhat similar extent in 1907, 

 instead of universal success? There are several factors respon- 

 sible for this condition of afifairs, some of which it is proposed 

 to discuss in some detail. The general lack of knowledge of 

 the nature of the fungus causing the disease and its method of 

 distribution, the intimate relation of the development of the 

 disease to weather conditions, improperly made bordeaux mix- 

 ture, inefficient or improperly constructed spraying machinery, 

 resulting in imperfectly covering the foliage, too few applica- 

 tions, or if the number of sprayings are sufficient, applied at the 

 wrong time, digging and storing too early if blight gains a foot- 

 hold on the foliage. 



RELATION OF' FUNGUS TO PLANT AND SPRAY TO FUNGUS. 



The late blight of potatoes is caused by a parasitic fungus, 

 a low form of plant life, which is made up of minute, almost 

 colorless threads which permeate the tissues of the healthy leaf, 

 killing the living cells of which the leaf is made and drawing 

 its nourishment therefrom. In the summer when once estab- 

 lished on a few leaves in a field it spreads very rapidly, if 

 weather conditions are right, by means of little reproductive 

 bodies called spores, which every blighting leaf produces by 

 thousands, if not millions. 



Certain soluble copper compounds in exceedingly minute 

 quantities are almost immediately fatal to these little spores as 

 soon as solutions containing such copper salts touches them. 

 The efficiency of bordeaux mixture as a fungicide depends upon 



* Me. Agric. Expt. Sta. Bui. 72, (iQOi) and Bui. 87 (1902). 



