-4- 



free moisture is present as rain, irrigation water, or dew. Where leaf blights are 

 severe, corn ears may be immature and chaffy, feed value of fodder is lowered, and 

 plants are predisposed to stalk rot. 



If leaf blights appear before or soon after tasseling, the yield, grain quality, and 

 feed value will be reduced. It will be at least three weeks before losses can be 

 evaluated. If the weather turns hot and dry, the spread of blights will be checked. 

 All three blights usually attack the older leaves first before moving to the upper 

 leaves. Heavily infected leaves turn brown and die. 



Northern leaf blight is recognized by long, elliptical, grayish-green to tan spots on 

 the leaves, up to 1-1/2 inches wide and 6 inches long. Ears are not infected, although 

 lesions may form on the husks. Northern leaf blight can now be found throughout 

 Illinois, but the buildup to date has been light. 



Yellow leaf blight is a new disease, occurring primarily in the northern part of the 

 Corn Belt. It can now be found in Illinois in scattered locations as far south as 

 the St. Louis area. It is favored by cool, wet weather and should not be a factor 

 until later this fall. Yellow leaf blight lesions are oval to elliptical in shape 

 and tan to cream in color, averaging about 1/2 inch long and 1/8 inch wide. Sometimes 

 a distinct yellow margin surrounds each spot. Yellow leaf blight lesions are very 

 similar to those of southern leaf blight (see below) . The two diseases can be 

 distinguished by putting pieces of infected leaves overnight in a tight plastic 

 bag with a moist paper towel. If yellow leaf blight is present, small black specks 

 (pycnidia) of the causal fungus appear scattered in the dead spots. 



Yellow leaf blight is closely associated with hybrids having Texas male-sterility 

 (Tms) , a character commonly used by the seed trade as a means of avoiding mechanical 

 detasseling. Tms brings susceptibility into inbreds and hybrids even though the 

 standard versions are more or less resistant. 



Southern leaf blight is an old disease that until 1969 was considered minor. A new 

 race of the causal fungus has developed to which inbreds and hybrids having Tms are 

 very susceptible. It is potentially the most serious disease of Illinois corn this 

 year. Lesions on the leaves range up to 1/2 inch wide and 1-1/2 inches long, being 

 oblong, parallel-sided, and grayish-tan to tan in color, surrounded by a yellow zone. 

 Many lesions have dark brown to purplish margins. 



The new race of southern leaf blight is causing lesions up to 6 inches long on the 

 stalks and ear husks, especially in seed production fields. Lesions penetrate the 

 husks and are now causing a powdery, charcoal-like rot of the ears in seed-producing 

 fields. Infection is widespread but less destructive in commercial dent corn hybrid 

 fields. Southern leaf blight is extremely destructive to corn throughout the south- 

 eastern states and can now be found in Illinois as far north as Chicago. It is most 

 widespread and damaging at present in southern and central Illinois. 



All three leaf blights are best controlled by growing resistant hybrids. Many inbreds 

 and hybrids are available that resist northern corn leaf blight. Illinois scientists 

 have found other types of male-sterile cytoplasm resistant to the fungi causing 

 southern leaf blight and yellow leaf blight. 



Seed treatment and crop rotation are not effective control measures because the spores 

 of the northern and southern corn leaf blighting fungi can be carried a number of 

 miles by wind currents. 



