244 SCIENCE AND FRUIT GROWING 



greater reduction in the disease than had the paste, and, accord- 

 ing to the tubers, a much smaller reduction, whereas as regards 

 the total sound crop obtained (the only point of importance) 

 they had both had exactly the same effect. 



It is evident, therefore, that the bolstering up of special 

 remedies by a display of illustrations of sprayed and unsprayed 

 plots, should be unhesitatingly condemned, as being misleading : 

 indeed, the appearance of the haulms is in any case, whether 

 spraying has been adopted or not, no criterion of the total yield 

 of tubers. It is well known that potatoes when grown in a virgin 

 soil show a phenomenal development of haulm, whilst the crop of 

 tubers is generally very small. 



Much of the work on potato-spraying done at Woburn was 

 directed to determine the proportion of Bordeaux paste which 

 would generally be equivalent in its effect to ordinary Bordeaux 

 mixture, and the results from that point of view have been stated 

 on p. 178. Some results of more general interest, however, were 

 obtained. 



In the first place it was clear that spraying sometimes, but 

 not always, caused an actual decrease in the crop of sound 

 tubers obtained, especially in seasons where there was not much 

 disease ; a fact which has already been noted by other ob- 

 servers. Thus, in 1895, there were 5 cases out of 25 where 

 spraying had slightly reduced the crop, and in 1896, 8 cases out 

 of 14. In 1913, when the total disease was as low as O'i2 per cent., 

 spraying had a more marked effect on reducing the yield, there 

 being a reduction of 5 per cent, when an average amount of 

 fungicide was used, and a reduction of II per cent, when the 

 amount of fungicide was increased threefold. In 1918, in the case 

 of some plots where there was no disease, and where Burgundy 

 mixture and Bordeaux paste, each at three different strengths, 

 had been used, the crops obtained were in the proportion of 91, 

 in and 127 where the strongest, medium and weakest spray- 

 fluids had been used, respectively. On the other hand, however, 

 there are exceptions found to such an action, for in 1911, where the 

 amount of disease was very small, the effect of spraying, though 

 somewhat insignificant, was in the direction of increasing the 

 crop (by 3*5 per cent.). 



Any deleterious effect of spraying, when such exists, is easily 

 accounted for by the fact that copper is toxic towards all plant 

 growth, and that it is only in cases where the harm done by it 

 to the plant is more than counterbalanced by the good done in 

 destroying the fungus, that the result will be beneficial. 



