CONFEEENCE ON SPRAYING OF FRUIT TREES. 



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of course it goes on developing as before. Again, many people, I believe, 

 have an idea that so long as the spraying mixture, whatever it may be, 

 is evident on the leaf, that leaf is perfectly safe from infection. That 

 also is a very misleading conception on the part of those who entertain 

 it in connection with spraying. I have repeatedly, after the end of a 

 month, when the leaf has been sprayed with Bordeaux mixture, known a 

 fungus to grow perfectly freely on the surface of the Bordeaux mixture. 

 That is a common experience, and not my own only ; it can be found 

 in almost every pamphlet dealing with the subject. Again Bordeaux 

 mixture will not prevent the development of a fungus that was present 

 previous to the spraying. Its development goes on much as usual. 

 Numerous instances are on record of that. The common scab fungus 

 causes defoliation all through the season. If you absolutely cover that 

 carefully — I mean, as you can do in the laboratory — with Bordeaux 

 mixture, giving it a far better covering than you get when spraying over 

 a ten -acre field, it goes on just as usual. Many others are the same ; it is 

 so with the pea scab and the scab of the broad bean and the scarlet 

 runner. The fungus may be painted over with Bordeaux mixture, but it 

 grows on and comes through, and will propagate as usual in spite of the 

 Bordeaux mixture. That is a point of importance, and it shows the 

 fallacy of holding that so long as the spray is obviously on the leaf your 

 tree is safe. Quite recently an American has been devoting consider- 

 able attention to this matter in connection with apple scab ; and pro- 

 bably apple scab is the one thing pre-eminent, the thing we are most 

 desirous of preventing, and the thing we are least successful in 

 preventing. He found that by taking apples where the scab was 

 present and covering them over carefully, so that every particle was 

 covered with Bordeaux mixture, from actual measurements the spots 

 under the Bordeaux mixture extended at exactly the same rate as at other 

 places that were not covered at all. This shows that there is perhaps 

 not as much good to be derived from fruit- spraying as we have been led 

 to believe. We expect too much from spraying. In the ordinary 

 course of things when spraying is done some result is expected. The 

 only benefit that can possibly be gained is to prevent to a certain degree 

 the extension of the disease, nothing more. 



We imagine when a leaf is sprayed that any spores falling on that 

 leaf will be destroyed. This is generally true so long as the Bordeaux 

 mixture, or whatever other medium is used, remains effective ; but no one 

 quite knows how long it remains effective. That depends on many con- 

 ditions. The most important point is the climate. The spray may be 

 washed off, or it may be induced to undergo such chemical changes that 

 it entirely disappears at a very early stage. On the other hand, I dare 

 say there are plenty here who have done practical work, and can say with 

 perfect truth that they have succeeded, by means of spraying, in preventing 

 an epidemic. Undoubtedly spraying has its benefits, but the benefits, 

 I am afraid, are very much lower than we are generally led to expect. 



I am sorry to say at the present day we have reached the point where 

 spraying has become a commercial business altogether. When a man 

 made his own spray solution, whatever it might be, it was most effective, 

 but now we are able to get ready-made stuff. I have not experimented) 



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