Figure 1. Bacterial leaf streak lesions on V4 corn plant leaves. Look for narrow wavy interveinal streaks on lower leaves. (Photos by Terra Hartman (left) and Tamra Jackson-Ziems)
Bacterial leaf streak disease was confirmed on a sample submitted to the UNL Plant and Pest Diagnostic Clinic from Adams County in south central Nebraska. The corn plants were at the V4 growth stage (fourth vegetative leaf) and represent the earliest that the disease has been confirmed in a field. However, the disease has been confirmed in emerging (VE) corn in the greenhouse, so it can likely develop anytime during the season.
Nebraska Extension Plant Pathologist Tamra Jackson-Ziems discusses bacterial leaf streak in corn on this week's Market Journal.
The disease is likely in other fields since its 2016 distribution was confirmed in 51 Nebraska counties. The bacteria can overwinter in Nebraska and may redevelop in the same fields where it occurred previously. There are also unconfirmed reports of the disease in Kansas and Colorado.
History
Bacterial leaf streak was reported for the first time in the United States in 2016 in several states, including Nebraska. Previously, the disease had only been reported on corn in South Africa and little research has been conducted on it. The pathogen, Xanthomonas vasicola, also causes gumming disease in sugarcane around the world.
Symptoms
Narrow brown to orange streaks or stripes develop between leaf veins and can be short (<1 inch) to very long (up to several inches in length). Lesions tend to develop on the lower (older) plant leaves initially and spread across those and to leaves higher on the plant over time. Yellow haloes also may be present around lesions when backlit. Symptom type and severity may vary somewhat between hybrids/varieties and have been observed in Nebraska on dent (field), seed, popcorn and sweet corn to varying degrees. No research results are available yet to predict its potential impact on yield. Hybrids and varieties may vary in their sensitivity to the disease which, in combination with favorable weather and growing conditions, will ultimately determine the disease severity and its impact on yield.
Figure 2. Bacterial leaf streak lesions may appear yellow when backlit by the sun and can be short or several inches long.
Diagnosis and Management
Diagnosing the disease in the field may be difficult because it appears similar to some other diseases and because the bacteria causing it are not visible to the naked eye and some microscopes. Some hybrids may produce lesions similar to those of gray leaf spot. However, gray leaf spot lesions may more commonly have straight, smooth margins, in contrast to those of this bacterial disease that often have wavy margins. It is possible to have this and other diseases, like gray leaf spot, on the same sample, further complicating diagnosis. For a diagnosis, we recommend and request submission of samples of this bacterial disease to the UNL Plant and Pest Diagnostic Clinic.
Because the disease is caused by a bacterial pathogen, we do not expect foliar fungicides to directly control it. Some bactericides, such as those containing copper, are labeled for use in corn, but their effects have not been studied on this disease. Activity of bactericides is often different from that of foliar fungicides. For example, most bactericides are contact products and not systemic, so they won’t be absorbed by plants, in contrast to many common foliar fungicides. Thus, bactericides may be washed off with rain or overhead irrigation and might require repeated applications for control, making them uneconomical or impractical for use in some corn crops. Other common pest management strategies, such as crop rotation, may be helpful, but the full host range of this pathogen is currently unknown.
