Rose Diseases 



329 



grayish. Careful cutting and burning of affected 

 material is suggested. 



The Crown Canker 



Caused by Cylindrocladium scoparium Morgan. 



Symptoms. Crown canker is perhaps one of the 

 most important diseases of roses under glass. Al- 

 though the percentage of roses that are actually 

 killed is rather small the effect of the disease is to 

 increase the financial loss by weakening the plants 

 and reducing the yields in marketable blossoms. The 

 disease first attacks the plants at the crown just 

 above the surface of the soil, producing lesions both 

 on the crown and on the roots. Infection often 

 starts at the place of union of the scion and stock. 

 The trouble is indicated by a slight discoloration of 

 the bark, which soon deepens until the affected tissue 

 becomes black and watersoaked (fig. 67, b.). As 

 the lesions increase in number, the crown of the 

 plant becomes girdled, and cracks appear in the 

 bark of the infected area, which is sunken and in 

 sharp contrast with the healthy bark surrounding it. 



Another constant symptom of the disease is the 

 punky consistency of the affected tissue. Although 

 this effect is marked in the crown, especially of the 

 diseased roots, the condition is further noticeable 

 in the bark and sap wood of the affected crown or 

 roots. The diseased roots send up suckers that are 

 weak, spindly, and pale. A close examination will 

 show that these, too, are affected at the point of 



