There is a new disease that may begin to impact corn yields throughout the US.
According to Kansas State University plant pathologist Doug Jardine, bacterial leaf streak, has made its way into corn crops throughout the heartland.
On Aug. 26, the US Department of Agriculture-Animal and Plant Health Inspection Service confirmed the presence of the new disease.
The bacteria that causes bacterial leaf streak disease is xanthomonas vasicola pv.vasculorum.
"APHIS does not consider it to be of quarantine significance and will treat it as other bacterial diseases of corn such as Goss’s bacterial blight," Jardine said in a press release.
First observed in samples submitted to the University of Nebraska-Lincoln Plant and Pest Diagnostic Clinic in 2014, the disease is thought to have occurred on corn in South Africa, but it has been most notably associated with gumming disease of sugarcane.
However, a lack of historical information and the appropriate diagnostic methods delayed its identification until APHIS positively identified the bacteria from a sample collected in Nebraska in August 2016.
It is currently not known how it made its way to the United States or how long it has been here.
"In Kansas, it has been positively identified in 12 counties, most of which are located on the High Plains," Jardine said. "Three additional counties have had corn with symptoms of the disease, but samples have not yet been confirmed definitively by DNA analysis."
If a corn leaf is infected it will have narrow tan to brown streaks that range from less than an inch to several inches long.
"To the untrained eye, the disease can look very similar to the common fungal foliar disease, gray leaf spot," Jardine said. "One diagnostic key is that bacterial leaf streak has narrow, wavy-edged lesions compared to gray leaf spot, which has very sharp, straight-edged lesions that follow the veins in the leaf.
"Sometimes the lesions occur close to the midrib; in other cases, they occur across the leaf blade."
An additional method to diagnose leaf streak is that when backlit, light passes through bacterial streak lesions in a translucent manner compared to gray leaf spot, which blocks the light and appears opaque.
With lesions appearing on lower leaves first, disease symptoms have been observed as early as growth stage V7 in corn.
As they spread to upper leaves, lesions can expand to cover larger areas and under favorable conditions.
Lesions may extend the entire length of the leaf and coalesce to form large, necrotic areas.
According to Jardine, it is not currently known how the disease has spread to so many states, but a current hypothesis is that it is seed transmitted.
Unlike Goss’s blight, it does not appear that it needs a wound to aid it in getting into the plant but movement within a field or from field to field may be by the bacteria blowing in the wind created by thunderstorms.
"Under what conditions is it likely to occur? By far the single largest scenario associated with the disease is corn being produced in a continuous, no-till, sprinkler-irrigated production system," Jardine said. "This is likely the reason that most positive counties in Kansas are in the western part of the state.
"That being said, the disease has also been found in furrow irrigated fields, as well as dryland fields in a strict corn-soybean rotation."
Jardine added that disease management options are currently limited no research has been conducted to date to determine if there will be any impact on yield.
Fungicides are not effective since it is a bacterial disease.
Residue management will not likely be an option except perhaps in southeast Kansas because of the highly erodible nature of most Kansas soils.
"We do not know how long the bacteria can reside in old crop debris, but observationally, it can survive through the rotational year to soybeans," Jardine said. "Observations in hybrid demonstration trials in Nebraska indicate that there are differences in hybrid response to the disease with some being much more susceptible than others. Long term, hybrid selection, as with Goss’s blight, will be the primary means of management."
Information on sample submission can be found at tinyurl.com/hm9eale.
"As with any crop disease," Jardine said, "samples can be submitted to the K-State Plant Disease Diagnostic clinic through any county or district extension office or directly to the clinic."