DISEASES OF ROSES 83 



disease, being first noted in Italy in 1824.^ It was probably present 

 many years before this date and has long been known to the rose- 

 growers of Europe. In 1825 the Hybrid-Perpetual began to take 

 first place in the rose world, and as this class is probably the most 

 susceptible to black-spot it is not surprising that references to the 

 disease began to appear more and more in articles on the cultiva- 

 tion of roses. 



Saccardo ^ notes the occurrence of black-spot in France, England, 

 Italy, Belgium, Germany, Austria, Portugal, and North America. 

 No special attention has been given the disease by American in- 

 vestigators until in more recent years when, due to the more intense 

 cultivation of the rose or the production of more susceptible varie- 

 ties, it has come to be considered the worst enemy of this plant. 

 Possibly the first report of the disease in America was by Scribner 

 (2) in 1888. Both Maynard (3) and Humphrey (4) record observa- 

 tions on the disease the following year. Subsequently the disease 

 has been reported as occurring in practically every part of the 

 United States and it is safe to state that black-spot exists wherever 

 roses are grown. 



Economic Importance. Black-spot is probably the most im- 

 portant of all the many diseases of the rose. It is both an enphy- 

 totic and an epiphytotic disease of out-of-doors plants, being more 

 or less abundant every year and in seasons especially favorable for 

 its development, attacking and defoliating a large percentage of all 

 garden roses. Under glass the disease is practically always present, 

 ready to become epiphytotic as soon as proper conditions of tem- 

 perature and moisture develop. The extreme susceptibility of 

 Hybrid Perpetual roses to black-spot is one of the factors contrib- 

 uting to their decrease in popularity. The great susceptibility of 

 the Pernetiana group to this disease threatens to be the limiting 

 factor in its popularity unless some practical methods of control 

 are developed. 



Symptoms. Although the lesions sometimes occur well down on 

 the petioles and even in the case of some varieties on all the aerial 

 parts of the plant ^ the disease is confined practically entirely to the 



1 Fries, E. Observationes mycologicae, p. 207. 



2 Saccardo, P. A. Sylloge fungorum 3:408. 1884. 



' ChifiQot, J. The extension of Marsonia rosae on rose bushes. Assoc. Franc. Avanc. 

 Sci. Comp. Rend. 43: 426-428. 1914. 



