82 MASSACHUSETTS HORTICULTURAL SOCIETY ■ 



usually have been studied by pathologists either as an incident to 

 other investigations or by mycologists interested in taxonomy. 

 Many recommendations for the control of diseases have been 

 made without due consideration being given to the conditions and 

 needs either of the commercial grower or of the fancier. Sprays 

 which will discolor foUage and buildings may be more objectionable 

 than the disease itself, with the result that growers have been 

 loath to use many of them even though their efficiency in suppress- 

 ing specific diseases has been established. Further investigation 

 of rose diseases is highly desirable. 



Black-spot. 



Probably the most common and destructive disease of the rose 

 is black-spot. It occurs wherever roses are grown, nearly all the 

 cultivated varieties both out-of-doors and under glass being affected, 

 although not all varieties are equally susceptible. Roses of the 

 Hybrid-Perpetual and Pernetiana groups are considered most 

 susceptible. Laubert and Schwartz (1) ^ hold that bushy sorts 

 are more susceptible than climbers and also that those with thin 

 leaves are more liable to attack. The writer has observed that 

 practically all bush roses, Hybrid-Perpetuals, Hybrid-Teas, Teas, 

 and Pernetianas, are more or less susceptible, while those of the 

 types Multiflora and Wichuraiana are comparatively free from 

 attack. Hybrids of Rosa rugosa and moss roses are rarely affected, 

 although Scribner (2) states that " moss roses and those with thick 

 rough leaves seem to suffer more than other kinds." This worker 

 may have confused an abnormal condition of the leaves of moss 

 roses known as " bronzing" with black-spot. ^ 



Names applied to the disease. Several names have been used to 

 designate the disease under consideration, among which are 

 black-spot, leaf-blotch, star-shaped leaf-spot, and rose-actinonema. 

 It is perhaps best known as " black-spot," this name being generally 

 accepted and adhered to both by scientific workers and growers. 



History and distribution. The black-spot of roses is not a new 



1 Numbers in parentheses refer to a bibliography at the end of this paper. 



2 Stone, G. E., and Smith, R. E. The bronzing of rose leaves. In Report of the botanist 

 Mass. Agr. Ex. Sta. Rept. 11: 156-159. 1899. 



