268 Diseases of Truck Crops 



The Organism. The mycelium is hyaline, non-sep- 

 tate, and in other respects not different from other 

 downy mildews. The conidiophores are long and 

 little branched (fig. 48 d, e), the conidia are hyaline, 

 elliptical to ovoid in shape, germinating by means of 

 motile zoospores (fig. 48 f-1). The oospores or sexual 

 resting spores are formed in the same way as in 

 Pythium (fig. 48 m, n, r), see p. 43. 



Control. Downy mildew is carried over in the seed 

 as dormant mycelium. Hence all shriveled seed 

 should be discarded. In badly infected fields, crop 

 rotation should be resorted to. The burning of trash 

 and old bean plants is also advised. Finally three 

 sprayings with 4-4-50 Bordeaux mixture during the 

 growing season will keep the disease well in check. 



RUST, see BEAN, p. 262. 



POWDERY MILDEW, see BEAN, p. 262. 



POD BLIGHT 

 Caused by Phoma subcircinata E. and E. 



As the name indicates, the disease chiefly attacks 

 the pods. Blight is indicated on them by the appear- 

 ance of large brown patches (fig. 48 o, p). The 

 pycnidia of the fungus are arranged in concentric 

 zones. In severe cases, the disease works from the 

 pods to the seed, considerably reducing the yield. 

 On the leaves the symptoms are the same as on the 

 pods. Spraying with Bordeaux will control the 

 trouble. 



