32 MISC. PUBLICATION 4 4 0, U. S. DEPARTMENT OF AGRICULTURE 



Soil rot is of commercial significance in long-distance shipments, 

 especially those sent from the Gulf States during the earlier months 

 of the year, when wet, soil-stained pods are packed. 



Irregular, reddish-brown lesions are produced on the roots and 

 stems of beans in the field. The pods are affected both in the field 

 and in transit. In the field those in contact with the soil usually 

 become infected at the end of the pod. The lesions are large, often 

 irregular in shape, and light brown with soft, badly rotted underlying 

 tissues (pi. 7, F). In advanced stages the seeds are discolored 

 (pi. 7, D). The larger lesions are often concentrically marked with 

 alternating light- and dark-brown zones and frequently become 

 covered with sclerotia. 



The presence of the fungus itself is the best diagnostic character. 

 The mycelium is white at first, but later deepens in color, passing 

 through yellow brown to deep chocolate brown. Most characteristic, 

 however, are the sclerotia or resting bodies. These appear first as 

 small, soft, cream-colored masses, later becoming large and irregular 

 and turning dark brown, similar to the sclerotia formed by this 

 fungus on potatoes, carrots, and other vegetables. 



Inoculation experiments with green bean pods have shown that 

 infection may take place in 5 days at 51° F., but the rate of develop- 

 ment of decay is very slow below 60°. Most rapid decay occurs in 

 green beans when the temperatures are between 75° and 90°. 



Although the causal organism is usually present in the soil, it 

 does not cause serious injury to growing plants unless the soil is 

 wet and the temperature is between 55° and 80° F. 



No really satisfactory method of controlling this disease in the 

 field is known. Green beans showing brown discoloration or water 

 soaking should be discarded before the crop is packed for shipment, 

 and sufficient refrigeration should be provided to maintain a tempera- 

 ture of 50° F. or below during transit. 



(See 6'^, 117, lift.) 



SUNSCALD 



The symptoms of sunscald and russeting at times are very similar 

 but with this difference: Sunscald occurs only in the field, whereas 

 russeting appears to occur primarily after harvest. Sunscald does 

 not occur so long as the pods are well shaded by the leaves. 

 If the leaves fall, whether because of disease or ripening, 

 sunscald is likely to occur on hot days with intense sunlight. The 

 actinic effect of the sun's rays, together with the high temperature, 

 causes the death of the more sensitive surface cells. The first indica- 

 tions of the disease are very tiny brown or reddish spots upon the 

 exposed surface of the pod. These gradually lengthen until they 

 become streaks which run across the pod diagonally and are more 

 or less parallel. The affected areas are water-soaked and brown at 

 first and may become sunken. Often the individual spots fuse to 

 form brown to reddish areas of varying size, which at times cover 

 most of the surface. 



The lesions, especially in the early stages, arc not easily distin- 

 guished from bacterial soot, but they always lack the greasy exudate 

 that often is present in blight lesions. 



