294 



Diseases of Economic Plants 



Blight ^^'^ (Pseudomonas sp.). ■ — This disease was described 

 by Burrill in 1889. 



It shows chiefly as a dwarfed condition which may occur 

 in spots m the field, varying in size from a few square rods 



to an acre or more. The 



affected plants finally turn 

 yellow, and most of them 

 die. 



The lowest roots of dis- 

 eased plants, in some cases 

 comprising half of the root 

 system, die. The stalk 

 near the base, when split 

 lengthwise, shows a uni- 

 form, dark color which 

 also appears in the upper 

 nodes in lesser degree. 



Rust {Puccinia sorghi 

 Schw.). — Corn rust seems 

 to have taken its place in 

 literature in 1815. It is 

 comparatively of slight 

 importance, since it does 

 not usually develop early 

 in the season, though 

 in exceptionally favorable 

 climatic conditions it may 

 do so. The brown sum- 

 mer spores appear first in 

 linear sori, and the black 

 winter spores come later 

 in the season. The cluster- 

 cup stage is found upon 

 the wood sorrel (Oxalis). 

 {Helminthosporium inconspicuum C. 

 blight gives a somewhat frostbitten ap- 



FiG. 155. — Portion of corn leaf show 

 ing sori of rust. 



Yellow-leaf '''' ''' 

 & E.). — This 

 pearance to the plants, producing also a thin olive-green 



