Hydrangea Diseases 273 



Diseases of Hydrangeas 



Hydrangeas are very hardy plants. They are sub- 

 ject to but few diseases, which are of little impor- 

 tance. 



Rust of Hydrangea 



Caused by Pucdniastrum hydrangea (B. and C.) 

 Arth. 



Rust is a serious disease on hydrangeas. The ure- 

 dinial and tetial stages of the causal organism are do- 

 ing the damage. Selby * was perhaps the first to 

 have observed the rust, although little more has been 

 added to our knowledge of it or of methods of con- 

 trol. 



The Organism. As far as is known Pucdniastrum 

 hydrangea has only two spore stages, the uredo and 

 teliospores. The uredinia are found scattered most- 

 ly on the under side of the leaf, their color dark 

 yellow to pale yellow. The peridium is delicate, the 

 cells are small, while the walls are thin throughout. 

 The ostiolar cells are somewhat elongated, and 

 slightly pointed, the spores are broadly elliptical to 

 ovate; the cell wall is thin and warty. The telia are 

 usually found on the lower part of the leaf in small 

 angular groups, that are rather flat and reddish 

 brown in color. Spores are formed in a single layer 

 within the epidermal cells or immediately beneath 

 it; the cell wall is thin, and a dark, cinnamon brown 

 in color. No methods of control are known. The 



'Selby, A. D., Ohio Agr. Expt Sta., Bui. 214: 402, 19x0. 



