junei7, i9i8 Sunscald of Beans 649 



On September 6, bean pods which showed very slight spotting and 

 some showing none at all were tied in muslin sacks and left until Sep- 

 tember 13. The leaves were removed and no shade covered the plants 

 at any time of the day. Four groups of these pods are shown in Plate 

 65, B, and are as free from spotting as when placed in the sacks. The 

 two pods at the left show slight traces, which was the condition on 

 September 6. 



On September 8 the original experiment was repeated on pods of the 

 Refugee Wax variety. The tables were constructed of stakes and muslin 

 sacks; and pods free from spotting were exposed and inserted in the 

 sacks. The experiment was discontinued on September 16, with the 

 same result as in the previous case. Plate 66, A, shows the results of 

 one of these trials. The pods were placed on a mirror for photographing. 

 On the right is one pod which was half -inserted in the sack, the lower 

 half showing no spotting, the upper half being heavily spotted. The pods 

 at the left were exposed on the table and are heavily spotted on the 

 upper surface; but the lower surface, as revealed in the image, shows no 

 spotting. The two pods at the center were not included in the experi- 

 ment, but hung naturally on the plant, partially shaded. 



In a field of the Hardy Wax variety, in which the leaves were yet green, 

 owing to late irrigation, plants were found which had been crowded over 

 by the wind. Exposed pods were spotted. On the stalks and branches 

 also, long, brown streaks were obser\''ed which appeared to be due to the 

 same cause. These streaks were only on the side exposed to the sun. 

 A plant of this type is illustrated in Plate 66, B. 



CAUSE OF THE DISEASE 



The spotting and streaking of the pods and the streaking of the stems 



and branches is due to sunscald. When the pods are shaded, as in 



leafy varieties, little or no spotting occurs. The tissue is bacteriologically 



sterile. 



ECONOMIC IMPORTANCE 



No loss is caused by sunscald. Bean pods have been found which 

 were so severely scalded that the seed coats within were slightly stained, 

 but no ill effects were to be observed. Seed saved from pods severely 

 scalded in 191 6 and planted in 191 7 were normal in every respect. There 

 was no decrease in yield, nor lack of vigor. The pods filled normally, 

 and scalding occurred again as it had done before. 



The danger is that the sunscald may be mistaken for bacterial-blight, or 

 that bacterial-blight may be disregarded for scald. Bean pods examined 

 at several places in the East were spotted very finely by spots closely 

 resembling the ones described above. They were diagnosed by patholo- 

 gists as bacterial-blight spots, because they were so common and had 

 the characteristics of incipient blight infection. Spots of some few 

 examined were not bacterial, and were believed to be sHght touches of 

 sunscald. 



