420 Diseases of Economic Plants 



blossoming, accompanied by destruction of infested refuse, 

 has proved a satisfactory treatment. 



Powdery-mildew (£'ri/s//>/ie cichoracearum DC, Oidium).— 

 This mildew occurs as white, flour-like spots upon the green 

 parts of the plant. It is not often serious, but if it should 

 become so, can readily be controlled by the means suggested 

 for rose mildew. 



Leaf-spot {Cylindrosporium chrysanthemi E. & D.). — 

 First described in 1893, this- closely resembles Septoria spot, 

 though it develops somewhat more rapidly and is conse- 

 quently more injurious. Often the leaves die and flowers 

 fail to form. Treatment is the same as for Septoria leaf- 

 spot. 



Gall (Pseudomonas tumefaciens) . — Galls upon the stems 

 of this plant have been proved by Smith and Townsend to be 

 due to Pseudomonas. Treatment has not yet been discussed. 



CINERARIA 



Rust (Coleosporium senecionis (Schum.) Fr.) is occa- 

 sionally serious. 



CLEMATIS 



Stem-rot ^^^' ^^^ (Ascochyta dematidina (Thuem.) Gloy.). — 

 Plants affected with this disease were first noted in 1883. A 

 leaf spot is produced ; the petioles are affected and the fungus 

 grows down to, and girdles the stem at the node. Diseased 

 leaves should be removed and the plant sprayed. Leaf-spot 

 (Cylindrosporium clematidis E. & E.). — This occurs on 

 clematis in propagating houses causing the loss of the lower 

 leaves. 



COLOCASIA 



Rot.^^*^ — Several kinds of rot occur on the cormels, 

 prominent among these are the Java black-rot (Diplodia sps.), 

 Powdery gray-rot (Fusarium), Southern blight {Sclerotium 

 rolfsii), Soft-rot (Bacillus carotovorus) . 



