Reacting to new corn diseases

​There have been several news releases concerning the occurrence of bacterial leaf streak on corn in the US Midwest.  Although it was noted in Nebraska in 2015, it was reported in 5 states in 2016.  In no cases has damage to yield been projected but there has been enough notice, I think, to everyone involved in the crop to be aware of the disease.  This is a proper response when a new disease distribution is identified. 
 
The photographs of symptoms show an early appearance similar to gray leaf spot (rectangular lesions between veins about ½ inch long) but later becomes as long as 2 inches, unlike gray leaf spot lesions.  Many corn diseases have distinctive symptoms that can make diagnosis easy by comparing with photos but this one, at least with early symptoms, is not easy.  It is best to have a public or private plant pathologist culture it to confirm if the pathogen is a fungus like Cercospora zeae-maydis, cause of gray leaf spot, or a bacterial such as Xanthomonas vasicola pv. Vasulorum, cause of bacterial leaf streak.
 
This has been a humid summer in northern Illinois that is conducive to the gray leaf spot fungus and likely to cause confusion with the new disease.  It would be an advantage, however, to get accurate appraisal of the occurrence of the bacterial disease however so seed companies can access the significance of the disease and differences among hybrids for susceptibility. It would be beneficial to know if this is just a mostly harmless disease that is easily controlled or if it is more serious.  This is a good time to look at fields while leaves are still green and to be aware of any leaf diseases. Public and private corn pathologists meet annually to discuss new information concerning corn diseases.  This will be a topic for the meetings in December 2016.