SUNSCALD OF BEANS ^ 



By H. G. MacMillan 



Assistant Pathologist, Cotton, Truck, and Forage Crop Disease Investigations, Bureau 

 of Plant Industry, United States Department of Agriculture 



INTRODUCTION 



The seed-bean industry is new in northern Colorado. In the Greeley 

 district eastern seed houses contracted for 3,000 acres in 191 6; 10,000 

 in 1 91 7; and it is estimated that 25,000 acres will be contracted for in 

 1 91 8. Forty thousand acres in Weld County were in beans (Phaseolus 

 vtdgaris), both seed and commercial, in 191 7, the acreage having been 

 distributed among 27 varieties. Yields of 35 to 45 bushels per acre 

 indicate that irrigation and climatic conditions are favorable to bean 

 production. Anthracnose is rare; rust appears only where rotation 

 has been neglected ; bacterial-blight is yet uncommon. 



Late in 191 6, before the beans had been harvested, a spotting and 

 streaking ^ of bean pods generally was observed. In all stages it had 

 the appearance of a bacterial infection. Microscopic examination was 

 made of the traumatic tissue ; but no bacteria, or suggestion of bacteria, 

 were found. Cultures were made on beef agar, potato agar, bean agar, 

 string beans, and in beef bouillon; but no organism developed, other 

 than an occasional contamination. 



THE DISEASE 



In northern Colorado beans are planted about May 20. By planting 

 60 pounds of seed to the acre in rows 28 inches apart a heavy stand of 

 vine is obtained. After three irrigations the pods are well filled and 

 approaching maturity. Usually no water is applied after the middle of 

 August. From this time on, the leaves gradually desiccate and curl 

 exposing the ripening pods beneath. Then the spotting appears. At 

 this period the green stage has passed, and the pods are whitening. 



The first indications of disease are very tiny brown or reddish spots upon 

 the upper or outer valve away from the center of the plant. These spots 

 gradually lengthen until they appear as short streaks running backward 

 and downward from the ventral toward the dorsal suture. In two days 

 the spots have increased to areas of brown water-soaked tissue, some- 



1 This problem was oritdnally taken up as a joint problem with Prof. W. G. Sackett, Bacteriologist of 

 the Colorado Agricultural Experiment Station, but his absence from the State in the fall of 1917 made 

 another arrangement necessary. However, the writer is indebted to Prof. Sackett for the results of some 

 microscopical and cultural study. 



2 This "streak" was first mentioned by (Sackett Sackett, W. G. diseases of beans. In Colo. Agr. 

 Exp. Sta. Bui. 226, p. 21-31, 6 fig. 1917-) 



Journal of Agricultural Research, Vol. XIII. No. u 



Washington, D. C. J'ine 17, i 18 



ob (647) Key No. G-147. 



