Identification of new occurrences of corn diseases in the USA rightfully gets attention of people growing corn. Since my introduction to corn pathology in 1971, I have witnessed to increased intensity of pathogen races for southern corn leaf blight, northern leaf blight, northern leaf spot, and common rust. We have seen increased widespread destruction of pathogens causing gray leaf spot, sudden occurrence of Goss Wilt that seemed temporarily controlled and the more recent reemergence in new areas. Head smut, once common in high plains of Texas suddenly showed up in areas of Minnesota and Canada. Eyespot, once known only in Japan, suddenly became common in Southeaster Minnesota and Wisconsin. Corn Lethal Necrosis caused by combination of Maize Chlorotic Mottle Virus and maize dwarf mosaic virus or wheat streak virus suddenly was found in Nebraska and Kansas, and more recently in central Africa. More recent attention has been drawn to outbreaks of bacterial leaf streak and tar spot.
Severe crop losses have been avoided after these diseases were acknowledged, resistance was identified, and cultural practices modified. Relatively quick identification of the disease, study of its dynamics, genetic diversity in maize, corn breeding efforts has allowed reasonable control of the new disease occurrences.
Genetic diversity works both ways, however, as breeders inadvertently select for other favorable traits, usually unaware that a new race of a pathogen, or environmental variable, exposes the newest corn hybrid to a disease. We usually only know of such a disease after it had increased in intensity sufficient to grab the attention of a grower or agronomists who has the diagnosis by a pathology specialist. How many years has that new race or pathogen been infecting a few plants in center of corn fields before it got attention? Bacterial leaf streak was identified in 2016 in 9 states. How long had it been present? After the problem of the race of fungus causing northern leaf blight that could overcome the Ht1 gene, it was reported in multiple locations across the Midwest USA.
Current corn growing practices should increase the probability that new pathogens are developing each season and noting strange lesions or other potential disease symptoms should be reported to specialists to set off further searches.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.