New Corn Disease Discovered in the U.S.
Found in nine states, bacterial leaf streak is making its way through cornfields across the Midwest. The disease still vexes researchers at several Midwest universities, who don’t know if or how it will impact yields this fall.
“We’ve seen upper leaves affected, and that’s what contributes the greatest amount to yield,” says Tamra Jackson-Ziems, University of Nebraska Extension plant pathologist. “We don’t want to create concern just yet; we don’t know what its impact will be.”
Researchers believe the disease came from South African corn, as it has been linked to gumming disease in sugarcane, too. Because it’s so new researchers can’t pin down exactly how it entered the U.S.
The disease has been identified in Colorado, Illinois, Iowa, Kansas, Minnesota, Nebraska, Oklahoma, South Dakota and Texas. Symptoms include tan to brown streaks in varying sizes along infected leaves.
“To the untrained eye, the disease can look very similar to the common fungal foliar disease gray leaf spot,” says Doug Jardine, plant pathologist at Kansas State University. “One diagnostic key is bacterial leaf streak has narrow wavy-edged lesions compared to gray leaf spot, which has very sharp straight-edged lesions that follow the veins of the leaf. Sometimes the lesions occur close to the midrib; in other cases, they occur across the leaf blade.”
You can also backlight leaves and see the light passing through; bacterial leaf streak will appear translucent.
Symptoms show up as early as V7, starting with lower leaves and extending to upper leaves. The disease is thought to spread from field movement and via wind from thunderstorms.
Because it’s a bacterial, leaf disease fungicides are not effective; treatment for the disease is still unknown.
“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 says.