FUNGI IMPERFECTI 



357 



Control. It appears that the only practical methods of prevent- 

 ing this disease are to obtain healthy plants at the outset, to avoid 

 planting where raspberries or other related plants have grown, and 

 to remove and burn old canes as promptly as possible. The results 

 with spraying have not thus far been successful. 



XLVIII. ROSE LEAF BLOTCH 

 Actinonema Rosa (Lib.) Fr. 



COBB, N. A. Black Spot of the Rose. Dept Agl. N. S. Wales. Miscel. Publ. 



(2d Ser.) 666: 2-27. ///. 1904. 

 SCRIBNER, F. L. Black Spot of Rose Leaves. U. S. Dept. Agl. Rept. (1887): 



366-368. pis. 8, 9. 



The rose leaf blotch, or spot, is perhaps the most common and 

 injurious rose fungus aside from the powdery mildew (p. 224). This 

 disease is characterized by more 

 or less irregular brown spots, fairly 

 well defined, on the upper sur- 

 faces of the leaves (Fig. 175), 

 varying from a few millimeters in 

 diameter to areas covering more 

 than one half the entire leaflet. 

 In this darkened area there are 

 distributed a small number of pyc- 

 nidia, producing numerous, ellip- 

 tical, two-celled, hyaline conidia. 

 This spot may be controlled by 

 the use of any standard copper 

 spray, but it is not, of course, de- 

 sirable to spray for a few weeks 

 preceding the blossoming period. 

 Control measures should there- 

 fore look to preventing the dis- 

 ease from securing a start previous to the blossoming season. 



There is considerable difference in the susceptibility of the dif- 

 ferent host varieties. As a rule the bushy sorts are more severely 

 injured and the climbing roses are often immune. If cuttings are 

 selected from healthy plants, even susceptible varieties may be 

 generally propagated with little fear of serious trouble. 



FIG. 175. LEAF BLOTCH OF ROSE 



