324 



FUNGOUS DISEASES OF PLANTS 



FlG. 155. COLLETOTRICHUM FROM BEAN: 



AN ISOLATION CULTURE. (Photograph by 

 Geo. F. Atkinson) 



a few dark colored setae are developed. 1 The conidia measure 

 1 5-19 X 3.5-5.5^. They germinate readily and usually become 



septate during the process. 

 Each conidium is inclosed 

 by a gelatinous envelope 

 which when dry glues it 

 to other spores or to any 

 object upon which it falls ; 

 when moist, however, the 

 spores are readily sepa- 

 rated and distributed. 



Control. Very diverse 

 methods of controlling this 

 important disease have 

 been suggested. Seed se- 

 lection is important, but it 

 is not sufficient to select 

 seed which do not appear 

 to be infected, for many 

 minute infections will be overlooked. It is desirable, therefore, 

 to select healthy seed from healthy pods, preferably from a field 

 which shows the disease slightly or not at all. Whetzel's experi- 

 ments thus far seem to 

 indicate that this latter 

 type of selection yields 

 most satisfactory results. 

 Spraying with Bor- 

 deaux mixture, 5-5-50 

 formula, is to be advised 

 when the disease ap- 

 pears early and when the facilities are at hand to make a thorough 

 application of the spray. Burning infected material is necessary ; 

 moreover, rotation of crops is important. 



1 The setae in this case are not commonly a conspicuous part of the acervulus, 

 and in a cursory examination of the fungus they may be sometimes overlooked. 

 In fact, this fungus was at first placed in the genus Glceosporium. It is possible 

 that climatic conditions or the texture of the host may be important in determin- 

 ing the relative number of setae. 



FIG. 156. COLLETOTRICHUM LINDEMUTHIANUM 



