Goss's Wilt Heads South
Corn Disease Confirmed in Louisiana
DECATUR, Ill. (DTN) -- Louisiana corn growers have received confirmation that Goss's bacterial wilt infected some fields in that state this season. Until now, the leaf disease was generally considered to be a problem in the Central and Western Corn Belt.
"Unless I have skipped something in the literature, this is the first report of Goss's wilt in Louisiana," said LSU AgCenter plant pathologist Clayton Hollier.
Samples were taken from cornfields in Madison Parish that had both classic leaf symptoms and disease spread pattern of Goss's wilt, he said. "During the 2011 corn growing season, there were reports of Goss's wilt in northeast Louisiana, but further investigation found that these were fertilizer burn, herbicide burn and drought symptoms that were widespread that year," Hollier noted.
Goss's bacterial wilt and leaf blight was first identified in three fields in Nebraska in 1969. Over the next several years, the disease was identified in Kansas, Colorado, Wyoming, South Dakota, Iowa and since then in Illinois, Wisconsin and now, Louisiana.
The pathogen overwinters on the soil surface in infested residue, which serves as the primary inoculum source for future corn crops. Injury to leaves is generally required for pathogen infection, especially that caused by hail, sand blasting or heavy wind.
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According to the University of Nebraska research, the pathogen can also be seed borne and seed transmitted, but transmission to seedlings has been demonstrated at low rates. It is not believed to be a major source of infection except that it can provide the inoculum for introduction into new locations.
Hollier said scientists are still fitting the puzzle together in Louisiana.
A local aerial applicator first noticed the 50-foot circle of affected plants in Madison Parish. Hollier said several circles of damaged plants radiating out from a central point suggests the disease was transmitted by seed. Yield losses ranged from 100% in the "epicenter" to minor, if any, losses at the edge of the circle.
He told DTN the affected area of Louisiana did endure some storms and damage. "Some of these situations had Goss's, but most of the time no obvious injury was noticed," he reported. The disease has also been confirmed in East Carroll, West Carroll and Tensas parishes.
Hollier said the disease has been identified in three DeKalb hybrids, DKC 66-94, DKC 64-69 and DKC 66-96. He added that so far, the disease was not widespread and only serious in localized areas.
In the more northerly Corn Belt, growers in Goss's wilt regions are encouraged to select hybrids that show good tolerance to the disease. Since Goss's has never been a problem in this region before, Hollier said there's been no opportunity to rate hybrids as to tolerance.
Monsanto spokesman Jeff Neu told DTN by email the company is "actively working to deploy current resistance genetics into the areas where Goss's wilt has been identified. These genetics provide good levels of resistance where they are now used in the DeKalb line-up," he said.
The Monsanto breeding pipeline also contains projects that would provide enhanced levels of resistance. Those projects are in Phase 3 of development -- a stage considered by the company to be "advanced development," which after 12 to 24 months is generally followed by a pre-launch phase. Neu said those projects will be deployed in areas at risk for Goss's wilt.
The environmental conditions in Louisiana are expected to be harsh on the bacteria because it is not native, Hollier said. "Overwintering survival is not expected with tillage and decomposition of residue. But we are dealing with nature, so there are no guarantees," he said.
Still, now that Louisiana corn harvest is nearly complete, Hollier encouraged growers to weigh how they might decrease the chance of Goss's wilt bacteria overwintering in their fields.
"Since the bacterium survives in infested residue, any type of tillage operation that buries residue to encourage decomposition may be effective in reducing the rate of new infections," Hollier said. This allows the soil environment and microflora (microorganisms, moisture, temperature, etc.) to break down that residue and reduce the inoculum, which needs the residue to survive.
Rotating out of corn into other crops such as soybeans or small grains will also help reduce primary inoculum sources in corn residue, he said. "In addition to corn, other hosts for the pathogen include green foxtail, shatter cane and barnyard grass," he said. "Therefore, weed control may also be important for disease control."
Pamela Smith can be reached at Pamela.smith@telventdtn.com
(GH/AG/CZ)
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