956 MICROBIAL DISEASES OF PLANTS 



BLADE BLIGHT or OATS 

 Pseudomonas avena Manns and Bacillus avetuz Manns* 



HISTORY AND DISTRIBUTION. A specific bacterial disease of oats 

 has been described by Manns in 1909. What appears to have been a 

 similar trouble, extending from the Atlantic coast west to Indiana, and 

 from the Great Lakes to the Gulf States, was observed as early as 1890 

 by Galloway and South worth. Its appearance was noted for the first 

 time in Colorado in 1915. 



SYMPTOMS. In the early stages of the disease there is "a yellowing, 

 beginning either as small round lesions on the blade, or as long, streak 

 lesions extending throughout the blade or even the whole length of the 

 culm and blades. In the advanced stages, the affected blades take on a 

 mottled to almost red color, which has been called 'rust' and 'blight.' " 



CAUSE OF THE DISEASE. The disease is produced by the symbiotic 

 growth of two bacteria whose activity is favored by rainy, humid, and 

 cloudy weather. One of these organisms, Ps. avence, alone, is said to be 

 capable of effecting the blight in a mild form, while the other, B. 

 avena, is nonpathogenic; but a mixture of the two germs results in an 

 aggravated attack. 



METHOD OF INFECTION. Infection takes place through the stomata, 

 the organisms being spattered on the leaves from the soil by rains. 

 Grain insects are also responsible for spreading the disease. 



CONTROL. It is believed that the control of the disease lies in the 

 selection of resistant strains. 



STEM BLIGHT OF FIELD AND GARDEN PEAS 

 Pseudomonas pisi Sackett 



HISTORY AND DISTRIBUTION. The disease occurs in several of the 

 Western States, particularly in the mountain valleys of the higher 

 altitudes. It was first observed in Colorado in 1915, where it caused a 

 loss of approximately one-third of the field peas in the San Luis Valley, 

 while in other parts of the State where garden peas are grown for can- 

 ning purposes, the crop was materially affected. 



SYMPTOMS. The plants usually show the infection before they are 

 8 inches high, and many succumb before they reach that size. Both 



* Manns, "The Blade Blight of Oats, A Bacterial Disease," Bull. 210, Ohio Exp. Sta., 1909. 



