142 Journal of Agricultural Research voi. xix. no. 4 



The lower leaves were mostly gone, but a general yellowing of the fields 

 was not marked. Only one field was so seriously affected as to show 

 heavy general blighting and large yellow spots i to 3 rods across. About 

 60 per cent infection of the lower leaves was typical for the fields through- 

 out this section. 



In Dodge County the halo-blight was much more abundant. Of the 

 37 fields visited all showed at least 20 per cent infection; 5 showed light 

 infection — spotting of the lower leaves of 20 to 50 per cent of the plants. 

 This infection, however, was evident from the road. Over half of these 

 fields showed heavy infection — 60 to 100 per cent — on at least the lower 

 leaves, and yellowed spots in the fields. The plants in these yellowed 

 spots had little normal green leaf area, and as many as 10 per cent of the 

 plants were entirely yellow and stunted. About one-third of the fields 

 showed 100 per cent infection of the lower leaves, the browned tips and 

 margins showing plainly and often giving a brownish tinge to the fields. 

 In two fields the lower two to three leaves were practically dead and the 

 upper leaves so badly spotted as to give a general yellow color to the 

 fields. In all fields visited in Dodge County blight was evident without 

 a close examination and was sufficiently severe to threaten the crop if 

 unfavorable weather conditions continued. New green leaves were just 

 beginning to appear. 



In Fond du Lac County, farther north, the plants were smaller — 6 to 8 

 inches high — and the blight was not heavy in most fields. Seven fields 

 showed only traces of blight on lower leaves — i to 30 per cent. One 

 showed 100 per cent infection on the lower leaves and another heavy 

 infection — 100 per cent — and a general yellowing of the field. 



In Columbia and Sauk Counties 10 fields showed a normal blue-green 

 color but had 20 to 100 per cent infection on the lower leaves. Ten other 

 fields showed yellow spots or a general yellowing of the fields. This 

 section was second to Dodge County in the amount of bacterial blight. 



Reports and specimens of plants from 35 counties in Wisconsin showed 

 that leaf lesions were general throughout the oat-growing sections of the 

 State and that a single disease, the halo-blight, was responsible for the 

 trouble. A similar condition was reported for the oat fields of southern 

 Minnesota, Iowa, northern Illinois, and Indiana. 



For several years previous to 191 8 this bacterial blight was observed 

 in Wisconsin oat fields, but there was never enough of it to attract par- 

 ticular attention. The cool, cloudy days and frequent rains of the 191 8 

 oat season proved to be just the conditions necessary to favor the develop- 

 ment and spread of the disease. The average rainfall for May, 191 8, 

 was 6.66 inches, or considerably more than the normal for that month 

 and greater than for any year since 1892. At Madison there were only 

 four clear days during the month, and at least four heavy rainstorms 

 were accompanied by strong, driving winds especially favorable to the 

 spread of the disease. During June the weather conditions were much 



