ENEMIES OF THE ROSE 91 



This fungoid parasite lives over winter in dead leaves of 

 roses only. For that reason, if for no other, all such should be 

 removed and burned. The spores develop and circulate with 

 the utmost alacrity, and, carried by wind, insects, or otherwise, 

 easily find lodgment on the rose leaves. Here they germinate 

 and soon make their way underneath the cuticle of the leaf 

 where they continue to hve throughout the summer and winter. 

 Each such spot in two weeks is capable of maturing thousands 

 of fresh summer spores, and each of these infinitesimal spores 

 may produce another spot which fifteen days later produces 

 another crop of spores and spots and so following. 



Thus will be seen the paramount importance of checking this 

 wasteful disease upon or before its first appearance, because 

 the spores may be present even though invisible to the unaided 

 eye. An ounce of prevention here may be worth much more 

 than the proverbial pound of cure a few weeks later. 



Suppose we could find and burn every dead rose leaf in sight, 

 we should stih need other preventive measures. 



"The one that has been successful in the control of black- 

 spot is that of protecting the rose by covering the leaf with 

 some fungicide that will prevent the spore of the fungus from 

 penetrating the cuticle. Spores need moisture for germination, 

 and under favorable conditions will send forth a germ-tube 

 and penetrate the leaf within a very few^ hours. Once within 

 the tissue, no treatment non-injurious to the leaf can be given 

 which will kill the parasite. The problem, then, is to have the 

 fungicide present on the leaf when the necessary moisture for 

 germination and injection is present. This means that the fungi- 

 cide must be apphed before rains; that it must adhere to the 

 leaf; that it must be so highly insoluble that it is not readily 

 washed aw^ay, but not so much so but that it will go into solu- 

 tion as needed; and that it must be fatal to the fungus and 

 uninjurious to the rose."* 



Bordeaux mixture has proved efficient (4 ounces copper sul- 

 phate and 4 ounces of unslaked hme to 23 9 gallons of water or 

 a prepared mixture to correspond). 



Another fungicide that has been found as effective as the 

 above, but which does not so much discolor the leaves, is the 

 "90-10 dust mixture" containing 90 parts finely ground sulphur 



* Prof. Massey, in the 1922 "American Rose Annual," page 83. 



