156 Diseases of Greenhouse Crops 



motile by means of flagella. It grows slowly on 

 gelatine which is not liquefied. On potato cylinders 

 growth is vigorous, resulting in a gray-white film 

 with no changes manifested in the substratum. 

 There is no gas production and the organism is 

 aerobic. 



Control. Infection begins at a place of injury 

 that has been produced by the bite or puncture of 

 insects. Hence, any attempt to control wilt should 

 first aim to control insect pests (see pp. 381-410). 



Downy Mildew, see Cucumber, p. 138. 



Powdery Mildew 



Caused by Erysiphe polygoni D, C. 



This disease is the same as the mildew which at- 

 tacks cuciraibers and numerous other hosts. Mildew 

 is prevalent on greenhouse melons. It is character- 

 ized by powdery white patches on the leaves. For 

 control, see p. 323. 



Mycosph^rella Wilt 



Caused by Mycospherella citrullina (Sm.) Gr. 



Symptoms. This form of wilt is often a serious 

 greenhouse trouble. Grossenbacher * found that in- 

 fection is localized at the nodes and not at the inter- 

 nodes. The injury from Red Spider or from other 

 sucking insects is perhaps responsible for opening 



•Grossenbacher, J. G, New York (Geneva) Agr. Expt. Sta. 

 Tech. Bui. 9: 197-229, 1909. 



