Report of State Board of Horticulture. 89 



others, and for this reason it is necessary to suit the strength 

 of the fungicide to the host-plant. Certain fungicides, like 

 bordeaux mixture, can not 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 SOMETIMES FAIL TO PREVENT DISEASE? 



There are several reasons whj'- spraying sometimes fails to 

 accomplish the results expected. It may be that the fungi- 

 cide 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 begin 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 witliout de- 

 stroying the diseased part of the host. The most that can 

 be hoped for in such cases is that the disease may be pre- 

 vented from spreading to the health}^ plants or plant parts. 

 If the spraying is not thorough, so that all parts of the host 

 are covered, 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 plant parts are developed and left un- 

 sprayed, 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. ' 



WILL SPRAYING PREVENT ALL PLANT DISEASES? 



Several plant diseases, of which "peach yellows" is an ex- 

 ample, are not, so far as known, produced by organisms, and 

 these diseases can be neither prevented nor controlled by fun- 

 gicides. 



Other plant diseases are prorbiced by bacteria that live in 

 the tissues of diseased plants. These minute organisms sel- 

 dom appear on the surface of the host-plant and consequently 

 would not usually be reached by spraying. Such a disease is 



