Great Plains farmers may see a halo effect in their corn fields this fall, but it sure isn’t a heavenly sign. The University of Illinois Extension recently discovered a new bacterial leaf streak from a DeKalb County corn field that has been positively verified by the USDA and has since spread to nine other Plains states.
Produced by the pathogen Xanthomonas vasicola pv. Vaculorum, the disease creates linear lesions between the veins on a corn leaf and often looks comparable to gray leaf spot symptoms. The results aren’t pretty. Warning signals often appear on the lower leaves and then progress up the plant.
“Bacterial leaf streak lesions are more irregular, often thinner and longer, will ‘bleed’ over the veinal border, and may have a halo when held up to the light,” said U of I Extension commercial agriculture educator Dennis Bowman.
Before 2016, the disease had only been prevalent in South Africa corn, although the pathogen has been attributed to causing a gumming disease on sugar cane in other countries. This year bacterial leaf streak has been found in Colorado, Iowa, Illinois, Kansas, Minnesota, Nebraska, Oklahoma, South Dakota, and Texas. DeKalb is the only county in Illinois positively confirmed for the disease.
Most of the fields that have tested positive have been under pivot irrigation. Later infections can also occur and show up primarily in the upper canopy. This was the case for the positive DeKalb sample which surveyed approximately 340 randomly-selected fields in transects across 68 of Illinois’s 102 counties.
According to the University of Nebraska CropWatch, foliar-applied fungicides used to manage gray leaf spot and other fungal diseases are not expected to effectively control the bacterial pathogen. While more research is needed on how the disease spreads and ways to prevent it, corn producers are advised to use standard management practices for bacterial diseases.
Tamra Jackson-Ziems, Nebraska Extension plant pathologist, suggests sanitation practices such as cleaning debris from combines and other equipment between fields to slow the spread to unaffected fields. Crop rotation or tillage may also help reduce infected corn debris and decrease the number of surviving bacteria.