Few cases of Goss's wilt this summer; could be back next year
By Jean Caspers-Simmet
simmet@agrinews.com
Date Modified: 09/25/2012 11:04 AM
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KANAWHA, Iowa —The Goss's wilt epidemic that hit Iowa last year failed to materialize this summer due to drought, said Alison Robertson, Iowa State University Extension plant pathologist at last week's ISU Northern Research Farm field day at Kanawha.
"Because of the drought, we saw very little Goss's wilt this year," said Robertson. "The disease occurs when splashing water containing bacteria enters wounds caused by hail, blowing soil or wind."
But that doesn't mean the disease has gone away.
Robertson found Goss's wilt in the research plots that she evaluates.
"Even though we didn't have ideal conditions, it can still develop," she said.
Continuous corn fields are at highest risk for Goss's wilt, especially when the disease has been observed previously, Robertson said. Other factors increasing risk are use of hybrids with low tolerance to Goss's wilt, minimal or no-till practices and severe weather.
Goss's wilt could be a problem next year, especially in fields that have a lot of residue and are planted to non-tolerant hybrids, Robertson said.
"It is still very important to select tolerant hybrids, especially if the field had Goss's wilt in 2011," she said.
Even in soybeans, it is likely that the Goss's Wilt-causing bacterium, Clavibacter michiganensis, which overwinters in infected corn residue, is present because corn residue usually remains in fields.
"I think it's highly likely that as long as the corn residue is there, the bacterium is present," Robertson said. "Even in fields that went to soybeans this year and are coming back to corn a tolerant hybrid should be planted."
While rotation and tillage may help, Robertson wouldn't recommend mold board plowing because soils need to be protected.
"The bacterium is picked up in aerosols and carried by wind and dumped," Robertson said. "Even if you buried all the residue in your fields, you could get it from your neighbor."
Goss's wilt symptons can be mistaken for Northern corn leaf blight, Robertson said. The way to tell the difference is that Northern corn leaf blight lesions are long and cigar-shaped and there is a clear margin between the healthy and diseased tissue. There is no clear deliniation with Goss's wilt. Freckles in the outside edge of a developing lesion are a characteristic symptom of Goss's wilt. If the freckles are held up to the sulinght, the light will shine through them so that they look translucent.
"You will still need to manage for Goss's wilt next year," Robertson said. "The best way is to use a tolerant hybrid. There are good hybrids with every company."
Goss's wilt can reduce yield from 5 percent up to 70 percent.
Robertson predicts that Goss's wilt problems will subside within five years.
"Up until we saw it reported in 2008 in eight counties in Iowa, I don't think it was here other than in a few fields," Robertson said. "I think there was a spread of 25 years where we dind't have Goss's wilt in Iowa. The reason we ended up with it is that a lot of popular hybrids were very susceptible. The gray leaf spot epidemic in the 1990s came about because everyone planted a highly susceptible hybrid. In the 1970s, Southern corn leaf blight was also related to susceptible genetics. In the next four to five years companies are really working to develop tolerance in hybrids."
Since a bacterium causes Goss's wilt, fungicides will not provide any protection. Robertson is researching fungicide/bactericides and natural products.