196 



planting, and an endeavor to destroy the conspicuous spore-masses of 

 this fungus will help to keep the disease in check. 



Brown-Spot 

 Caused by Physoderma zeac-maydis Shaw 



This disease is usually of minor importance in Illinois. It was first 

 discovered here in 1911/ but the locality in which it occurred is not 

 known. A specimen has been preserved which shows that it was present 

 in Champaign county in 1913. 



Brown-spot is now known to occur in 26 counties with the distribu- 

 tion shown on Map 19. Although our losses from it are not usually 

 great, it may in unusual seasons become so severe as to do serious dam- 

 age. This was the case during 1923, when an examination of 15 fields 

 distributed among 10 counties and including 381 acres showed an aver- 

 age of 83.1 per cent of the stalks to be diseased. 



The fact that this disease can, under favoring conditions, produce 

 such severe infections emphasizes the need for keeping it under con- 

 trol. In general this depends upon the usual sanitary practises of crop 

 production — clean fields, good seed, and the disposal of diseased plants 

 elsewhere than in manure. The field notes summarized in Table 28 

 indicate that the Yellow Dent corn commonly grown throughout most 

 of the state shows the greatest resistance under field conditions, and 

 Democrat comes next. Certain special varieties appear to show high 

 susceptibility. Should the brown-spot disease become a serious menace 

 in any district where unusual varieties are commonly grown, a change 

 to Yellow Dent or Democrat may be found advantageous. 



Rust 



Caused by Puccinia sorghi Sclnv. 



This disease is similar to the rusts of other cereals. It attacks the 

 leaves and produces short rusty-red stripes. The fungus causing it has 

 an alternate stage which occurs on the wood sorrel (Oxalis), but this 

 stage has never been found in Illinois. Corn rust probably overwinters 

 by means of its summer spores. 



Specimens collected by A. B. Seymour in 1881 and 1882 show that 

 corn rust was ])rescnt then in at least eight widely scattered counties in 

 the northern half of Illinois. In 1911 Burrill recorded its presence in 

 Montgomery county, and in 1912 in Union county; E. F. Cuba collected 

 it near Galesburg in 1919; and a further collection was made in Cham- 

 paign county in 1919 by H. W. Anderson. At present it is known to 

 occur in the Ki counties shown on Maji 20. 



' Bairctt, J. T. I'husodcrma cfnc-iiiai/rfis Sliaw. in Ulinoi.*. riiytopathology 3: Tl. 

 191.'?. 



