Bacterial leaf streak is spreading and was found in across most of Nebraska this year, including Lincoln County and neighboring counties. Now researchers have determined that oats, sorghum, some pasture grasses and weeds may be able to transmit the disease to corn. No control methods have been identified yet.
Mark Spurgin of Paxton said he found the disease in areas of each of his corn fields this year. With varying conditions across the fields, and different corn hybrids, actual yield reductions are impossible to quantify. However, he guessed that it made a five-bushel difference. It could have been worse. With good crop growing conditions the disease “just didn’t progress” this year as it does some years, when it can “take the whole plant.”
University of Nebraska-Lincoln plant pathologist Tamra Jackson-Ziems, stationed in Lincoln, said university researchers are studying chemical treatments, crop rotation and tillage to combat bacterial leaf streak.
“We’re working as fast as we can to find answers,” she said.
They have identified several alternate hosts for bacterial leaf streak.
Terra Hartman is a UNL graduate research assistant working on the project. She said they observed the disease in oats and sorghum in the lab, but not yet in fields, and are not sure of the yield loss potential in those crops. However, producers may want to avoid rotating with oats or sorghum in areas where the disease has been identified in corn fields, she said.
Several pasture grasses and weeds are also alternative hosts for bacterial leaf streak, Hartman said.
“We sprayed down the plants with a suspension of the bacteria and water, and looked for symptoms” to develop, she said. If symptoms appeared on a plant, they isolated bacteria from leaf tissue. They followed that with a PCR test, a form of DNA analysis. Hartman said a certain DNA sequence is specific to this bacterium, and if it is present in the samples, it will replicate under conditions of the test.
The procedure has confirmed that big, sand and little bluestem; Indiangrass; orchardgrass; timothygrass; western wheatgrass; rice; and tall fescue are alternative hosts, along with the weeds downy brome, bristly and green foxtail, yellow nutsedge, shattercane and johnsongrass. Barnyardgrass was not shown to be a host, said Hartman.
The greenhouse work is being followed by field testing; so far, big bluestem and bristly foxtail have become infected when exposed to the bacterium in field settings.
Jackson-Ziems said bacterial diseases can be hard to control with chemicals, because bactericides are not readily absorbed into the plant and they wash off when it rains or the field is sprinkler-irrigated. Another problem is that infection can occur through plant openings, called stomata, on both surfaces of the leaf, but it is difficult to spray the lower surfaces.
Spurgin said he tried a product on two of his pivots. SaniDate was aerially applied to half of one field and OxiDate applied through the pivot on half of the other field. The products contain concentrated hydrogen peroxide and peroxyacetic acid as active ingredients. He said he will have a better idea after yield data is analyzed, whether the treatments helped.
Hartman said she hopes corn breeders develop hybrids resistant to bacterial leaf streak: “That would help a lot.”