112 Diseases of Greenhouse Crops 



beans. During a period of several hot humid days 

 the disease may suddenly break out in great se- 

 verity. Usually withering and decaying of stems 

 and pods where the plants are thickest is the first 

 symptom that attracts attention. On closely ex- 

 amining infected stems and pods, we find that they 

 are watersoaked, and overrun by a white mycelial 

 growth on which appear numerous hard, black scle- 

 rotia. In the field, the Black Valentine snap bean 

 seems to be more resistant to rot. For a description 

 of the causal fungus and methods of control, see let- 

 tuce drop, p. 150. 



Powdery Mildew 



Caused by Erysiphe polygoni D. C. 



Symptoms, Powdery mildew is a serious bean 

 disease. It is characterized by white, mealy patches 

 on the surface of the leaves and stems. The foliage 

 soon turns yellow and dry. Powdery mildew may 

 be controlled by dusting the plants with flowers of 

 sulphur. Care in the proper amount of watering and 

 ventilation will also help to keep it in check. 



Anthracnose 



Caused by ColletotricJium Undemuthianum (Sacc. 

 & Magn.) B. and C. 



Symptoms. Anthracnose is so characteristic that 

 it cannot be mistaken for any other disease, except 

 perhaps the blight. In light attacks, the seeds are 



