Rose Diseases 319 



The Bronzing of Leaves 



Cause, Physiological. 



Symptoms. This trouble commonly affects 

 grafted varieties of the Tea, Bride, and Brides- 

 maid. By some growers the disease is often mistaken 

 for a stage of the black spot caused by Diplocarpon 

 rose. Bronzing produces a mottled bronze color- 

 ing of the foliage. Later the mottling becomes 

 more prominent in the form of spots, while the ad- 

 joining tissue turns pale yellow. Frequently the 

 entire leaflet becomes bronzed with no yellowish 

 color apparent. At times the affected leaflets and 

 leaf stalks drop to the ground. The cells of the 

 affected tissue contain an abundance of calcium oxa- 

 late crystals, a condition that indicates poor nutri- 

 tion. Bronzing is usually confined to two places. 

 First, where a stem has been cut and a new branch 

 has started the leaf at the base begins to bronze; 

 second, where an eye or an auxiliary bud has been 

 rubbed off, the leaf generally becomes bronzed. 

 From studies made at the Massachusetts Station* 

 there seems to exist a difference in susceptibility 

 between young and old plants. Bronzing may be 

 expected to occur on young plants. It is also prev- 

 alent both on plants which are forced too rapidly 

 and on weak stock. The selection of strong, hardy 

 stocks and care in feeding will prevent the trouble 

 from becoming serious. 



* Massachusetts Agr. Expt. Sta. (Hatch) Ann. Rept.: 156-1591 

 1899. 



