Spray Calendar. 67 



fects of spraying are cumulative ; that is, tlie effects of spraying 

 and keeping fruit trees free from disease this year will give a bet- 

 ter crop next year. Even with trucking crops that die down in the 

 fall the danger from disease next year in a particular field will be 

 greatly reduced if the field is kept free from diseases this season. 



DOES SPRAYING SOMETIMES INJURE FOLIAGE AND FRUIT? 



If fungicides are not properly made they will burn the foliage 

 and discolor the fruit. It is a well-known fact that the foliage on 

 some plants is much more tender than it is on others, and for this 

 reason it is necessary to suit the strength of the fungicide to the 

 host-plant. Certain fungicides, like bordeaux mixture, cannot be 

 used in spraying fruit that is nearly ripe, since the fruit would be 

 stained by the mixture, and thereby rendered unsalable. 



WHY DOES SPRAYING SOMETLSIES FAIL TO PREVENT DISEASE ? 



There are several reasons why spraying sometimes fails to accom- 

 plish the results expected. It may be that the fungicide was not 

 properly made; that the spraying was not done early enough in 

 the season, or that the applications were not thorough or persistent 

 enough. If we wait until we see the disease at work before we be- 

 gin spraying, our efforts will not result in success, for the reason 

 that when we see the disease it is certain that the fungus spores 

 have germinated and the fungus has grown into the affected part 

 of the host-plant. In such cases it is impossible to destroy the 

 fungus without destroying the diseased part of the host. The 

 most that can be hoped for in such cases is that the disease may be 

 prevented from spreading to the healthy plants or plant parts. If 

 the spraying is not thorough, so that all parts of the host are cov- 

 ered, spores may fall upon the unprotected parts and grow as 

 readily as if no fungicide had been used ; or, if the applications are 

 not frequent enough, so that the fungicide is washed off, or new 

 planfparts are developed and left unsprayed, attacks of fungi may 

 take place as readily as if no spraying had been done. It should be 

 remembered that no fungicide will restore any plant part once 

 destroyed or injured, hence the necessity of preventing attacks of 

 fungi, and this can be done by an early, thorough, and persistent 

 use of fungicides. 



