lyo Journal of Agricultural Research voi. xix, no. 4 



the halos of oats in that they form "circular chlorotic areas" 2 to 3 cm. 

 in diameter with minute brown centers. The oat lesions, however, have 

 no water-soaked borders, and the affected tissues do not fall out as in 

 tobacco wildfire. A white organism has been isolated from these lesions 

 which differs from the halo-blight organism in the points mentioned 

 below : 



HAXO-BLIOHT ORGANISM. 



One to several polar flagella. 



Single to long chains. 



2.3 by 0.65 M- 



Capsules. 



Odor in agar stroke. 



Casein not precipitated in litmus milk. 



Ammonia produced. 



Thermal death point 47° to 48° C. 



TOBACCO ORGANISM. 



One polar flagellum. 



Single to chains of five elements. 



3.3 by 1.2/1. 



No capsules. 



No odor in agar stroke. 



Casein precipitated in litmus milk. 



Ammonia not produced. 



Thermal death point 65° C. 



The halo lesion so characteristic of this oat disease does not occur in 

 the blackchaff disease of wheat (<5-o) or the bacterial blight of barley 

 (2), while the oat disease lacks the translucent water-soaked stripes 

 of these diseases as well as the exudate so abundant in both. R. H. 

 Rosen has recently published a preliminary note on a bacterial dis- 

 ease of foxtail (4), which he thinks may be similar to the halo-blight 

 of oats. His description of lesions as dark brown spots or streaks, 

 however, makes it probable that if it is similar to either bacterial disease 

 of oats it would resemble stripe-blight rather than halo-blight. The 

 writer has not observed halo lesions on foxtail and in two sets of field 

 inoculations has obtained no infections on foxtail with the halo organism. 



CONTROL MEASURES 



The evidence that the halo-blight of oats is seed-borne seems conclu- 

 sive. However, no practical method of seed treatment has, as yet, 

 been found which will entirely control the disease. Treatment with 

 formalin for smut controls halo-blight to a marked extent but not entirely. 

 In 191 7, treated seed of 33 Wisconsin varieties did not show a halo lesion 

 throughout the season, while the same untreated varieties all showed 

 some halo-blight. In 1918, 44 treated varieties of Wisconsin oats devel- 

 oped primary lesions which, however, were later and fewer than on the 

 same untreated varieties. Even when the blight was most severe it 

 was only about half as heavy in the treated plots as in the untreated. 

 The plot from Wisconsin No. 14 treated seed showed very few primary 

 lesions and little secondary spotting except in patches about these pri- 

 mary lesions. This would indicate that soaking for three hours in i to 

 320 formalin kills many but not all of the organisms on the seed. In 

 Jefferson County, Wis., where most of the seed was treated for smut, the 

 blight during the 191 8 season was much less abundant than in Dodge 

 County, where seed treatment was not general. 



