Diseases op the Potato. 815 



had received the extra treatment. From this it would seem that 

 the last application made to section 2 was of minor importance. 

 The vines at that time had practically completed their growth, so 

 that there was little new foliage exposed to the disease. The rain- 

 fall had also been slight, and the Bordeaux mixture could still be 

 plainly seen upon all sections treated with it. 



The potatoes were dug September 26. Since the sections varied 

 somewhat in size, the yield of each has been estimated upon the 

 proportionate jield per acre, this furnishing a more convenient basis 

 for comparison. The result was as follows: 



Section 1. Old Bordeaux mixture, 332 bushels per acre. 

 " 2. Fresh Bordeaux mixture, 350 bushels per acre. 

 " 3. No treatment, 284 bushels per acre. 



" 4. Copper chloride mixture, 297 bushels per acre. 



The apparent gains from the treatments of the sections were 

 accordingly, 1-48 bushels; 2-66 bushels; 4-13 bushels. The ad- 

 vantage derived from the copper chloride mixture is so slight that 

 it promises little practical value. The results obtained with the 

 Bordeaux mixture, however, are more encouraging, and seem to 

 indicate that it may be possible to spray for the early blight, although 

 the margin may at times be close. 



To what extent these gains were due to the prevention of injury 

 to the ilea-beetle it is difficult to say. The vines which were most 

 thoroughly sprayed with the Bordeaux mixture did not escape the 

 attacks of this insect, as could be seen by the many pits which re- 

 mained as witnesses of its presence. Untreated plants suffered 

 more severely, as they did also from the early blight. The probable 

 action of the Bordeaux mixture thus appears to be two-fold. In 

 the first place it prevents to a very considerable extent injury from 

 the flea-beetle ; in the second place it prevents the entrance of the 

 macrosporium into tissues which have suffered from the work of 

 the insect, and also protects those which are made susceptible to the 

 disease in other ways. It is certain that the fungus was very abun- 

 dant in the foliage of untreated plants, and it seemed probable that 

 the value of the mixture was just as great in preventing injury 

 from this source as it was in protecting the leaves from the attacks 

 of insects. 



Plot II. This plot was also upon the University farm. It con- 

 tained just one-third of an acre, and was planted 1o several varieties 

 of potatoes, some of which were considerably earlier than others. 



