May IS. 1920 Halo-Blight of Oats 141 



some spotting. During the last week in May and the first week in June 

 all untreated plots looked yellowed or slightly browned when viewed 

 from a distance. Practically every first leaf and half of the second 

 leaves were yellowed and dead. Many leaves had yellowed, shriveled 

 tips and margins, and single lesions were abundant on the upper leaves 

 of many varieties. 



Every field about Madison showed some blighting. Usually the 

 brown, dead leaves were easily seen from the road, and 100 per cent of 

 infection was not at all uncommon. Some fields south of Madison 

 showed distinct yellow spots from a yard to a rod or more in diameter. 



One field of oats near Monroe, Wis., visited May 29, was so badly 

 blighted as to show from a distance a general yellowing with scattered 

 patches of more marked yellow. Closer examination showed abundant 

 halo lesions, every plant being infected. About 3 per cent of the plants 

 were yellowed throughout, the outer leaves were water-soaked and dead, 

 and som.e whole plants were stunted to such an extent that their recovery 

 seemed doubtful. On the remaining 97 per cent of the plants the outer 

 two to three leaves were collapsed and dead, and the others showed 

 scattered halo lesions in varying stages of development. Where the blight 

 was farther advanced the leaves were broken over and the tips shriveled 

 and brown. Other leaves show^ed typical, conspicuous, isolated halo 

 lesions which were central or marginal, covering one-half to the entire 

 width of the leaf blade. The plants in this field showed no marked red- 

 dening. They had been badly beaten by recent driving storms. Two 

 other oat fields in the vicinity showed a normal stand, but the halo-blight 

 was abundant. No plants remained uninfected, but nevertheless none 

 were stunted or entirely yellowed, and chances for recovery were much 

 better than for the field described above. The blight was general through- 

 out the section about Monroe, and the two fields last mentioned probably 

 represented the average. This yellowed condition of oat fields in this 

 section was first evident May 26 and was reported by a number of farmers. 



From May 3 1 to June 2 oat fields were visited by the writer in five coun- 

 ties of southern Wisconsin. More than 130 fields were inspected, and 

 every one showed halo-blight varying in amount from a fraction of i per 

 cent to 100 per cent, the latter being much the more common. The 

 amount varied not only in individual fields but also conspicuously in 

 different counties. 



In Jefferson County 26 fields were visited. The oats were about half 

 grown. One-fourth of the fields showed only scattered lesions on the 

 lower leaves — an infection of i per cent or less. About one-half of the 

 fields showed a general spotting of the lower leaves on from 60 to 1 00 per 

 cent of the plants. In some cases the infection was in patches from 2 

 to 6 feet in diameter, where every plant had all but the last one or two 

 leaves badly spotted. A few fields showed general and heavy infection 

 of 100 per cent of the plants. Even the upper leaves were spotted. 



