314 Diseases of Greenhouse Crops 



prefer a soil consisting of fibrous loam, one-fourth 

 of which is well rotted cow manure. Poinsettias 

 require frequent repotting to prevent them from be- 

 coming potbound. The night temperature should 

 never go down below $5 degrees F. As the plants 

 advance in age, the temperature is raised to 65 or 

 J J degrees. A few days before Christmas the stock 

 should be ready and the temperature lowered to 

 50 degrees F. Great care should be exercised to 

 prevent the potted plants from becoming either 

 overwatered or too dry. Poinsettias that are to 

 be used for cut flowers should have the stem end 

 dipped in hot water for a few moments and then 

 placed in cold water. This procedure will cauter- 

 ize the wounds and thus will add to the keeping 

 qualities of the blossoms. 



Diseases of Poinsettias 



Poinsettias seem to be remarkably free from dis- 

 eases. This is especially true as the plants outgrow 

 the cutting stage. 



Collar Rot 



Caused by Rhizoctonia solani Kuhn. 



Symptoms. The trouble is confined mostly to 

 cuttings that have been planted in an infected soil. 

 The lesions unite and in nearly every case form a 

 collar around the stem on the surface of the soil. 

 The collar formed is narrow, depressed, and dark 

 in color. For a description of the causal organism 

 and methods of control, see p. 20. 



