VII 



BEAN 229 



the diseased part. It also reproduces by oospores. It 

 can be controlled by careful selection of seed and 

 rotation of crops. Bordeaux mixture can be used 

 advantageously on small plantings. 



Powdery Mildews. - - These diseases are quite 

 abundant in the tropical and subtropical countries. 

 They produce the characteristic whitish growth on the 

 leaves which causes them to fall prematurely. Usually 

 only the conidial stage occurs in tropical countries. As 

 a rule these diseases are not severe, but they sometimes 

 cause considerable loss. They can be readily controlled 

 by the use of Bordeaux. 



Rust. This is a true rust disease, caused by 

 Uromyces appendiculatus, (Pers.) Lev. It is well 

 known and widely distributed throughout the bean- 

 growing districts of the world. The mycelial threads 

 penetrate the tissues of the host, finally coming to the 

 under surface of the leaf and forming the characteristic 

 blisters containing the spores. There are two kinds 

 of spores, the brown uredospores and the black teleuto- 

 spores, which are formed later. In most cases this 

 disease is not of much importance, but late in the 

 season it may cause an excessive dropping of foliage, 

 resulting in the early maturity of the pods and 

 shortening of the crop. It can be controlled to some 

 extent by careful selection of seed from healthy plants 

 only, by the destruction of the rubbish of the field, 

 and by the use of Bordeaux on small areas. This 

 disease also attacks the cow -pea, and other related 

 plants. 



Leaf Spots. Beans also suffer more or less from 

 Cercospora and other leaf-spot fungi, but as a rule they 

 do not prove serious. 



Rhizoctonia Rot. This disease, which is so common 

 in tropical countries, attacks the beans. It is 

 most severe in warm, wet weather. It may cause a 

 " damping off" of the seedlings, and it may attack the 

 stems and pods of the older plants. On the stems it 

 produces a dry-rot canker which extends to the pith, 



