Corn survey reveals positive sample in DeKalb County. Several weeks ago in cooperation with the USDA's Animal and Plant Health Inspection Service (APHIS), personnel from University of Illinois Extension, the Illinois Natural History Survey's Coordinated Agricultural Pest Survey and Illinois Department of Agriculture conducted a survey of production corn fields in two-thirds of Illinois' 102 counties.
What we were looking for is symptoms of a disease called bacterial leaf streak. Like many common names for plant diseases, bacterial leaf streak describes just what is happening; a bacterium (Xanthomonas vasicola pv. vasculorum) causes streak-like lesions on infected leaves. While this disease had not yet been observed in Illinois, it had previously been observed in Nebraska and in seven other states to the West.
While several leaf samples from Illinois were sent in to the USDA lab for molecular diagnostic testing, only one sample tested positive for bacterial leaf streak, leaves from a field in DeKalb County in North-central Illinois.
I personally surveyed production corn fields in six counties in Western Illinois. While none of the surveyed fields were positive for bacterial leaf streak, this in no way implies that the disease may not be present in these counties.
What does bacterial leaf streak look like? Bacterial leaf streak lesions can sometimes be confused with those of the prevalent fungus-caused disease Grey Leaf Spot. Grey leaf spot lesions are bordered by leaf veins and tend to be rectangular in shape. Bacterial leaf streak lesions tend to be less rectangular and lesion margins can be wavy, sometimes growing across leaf veins (Figure). They can also be thinner and longer than gray leaf spot lesions and surrounded by a yellow halo that can be observed when leaves are backlit.
What if I suspect bacterial leaf streak in my corn? Scouting fields before the crop matures can provide valuable information. While the days that are available for scouting are limited, knowledge of whether your crop is positive for this disease can allow one to proactively practice sanitation measures such not moving infected crop debris to fields in which plants have not had the disease.
The disease is new enough in the U.S. that plant breeders have not had sufficient time to screen inbred lines or hybrids for genetic resistance or susceptibility. While management practices fundamental to managing other bacterial diseases are recommended (crop rotation, sanitation and tillage), there has not been sufficient time to study the efficacy of these or other management practices.
Submitting samples to the Plant Clinic. Now that the disease is known to be present in Illinois, there is a desire to understand just how widely distributed the pathogen may be. If you suspect Bacterial leaf streak in your corn, submit a sample to the University of Illinois Plant Clinic.
Kirk Broders et al. 2016. Bacterial Leaf Streak.
Tamra Jackson-Ziems. 2016. UNL CropWatch. Bacterial Leaf Streak of Corn Confirmed in Nebraska, Other Corn Belt States.USDA-APHIS Aug. 26, 2016. Statement on Xanthomonas vasicola pv. vasculorum