A leaf disease that has shown up in many Iowa cornfields this growing season is Goss's Wilt. This disease was first reported in Iowa in 2006 and since then there has been a steady increase in the prevalence of Goss's Wilt in the state.
"Goss's Wilt is caused by a bacterium and that means there are no known rescue treatments to control the disease," says Alison Robertson, Iowa State University Extension plant pathologist. "Applying a foliar fungicide will not help reduce disease development or protect yield."
Goss's Wilt usually occurs in small patches within a field or it may cover the entire field. "When it does cover the entire field, we often find that the disease was a problem there in the preceding years," she explains.
Goss's Wilt has distinctive freckles, don't confuse it with other diseases
"Goss's Wilt has very distinctive freckles associated with the symptoms. Don't confuse Goss's Wilt symptoms with those of heat stress or other symptoms or diseases that can occur on corn."
It's important to assess the actual damage caused by the disease, similar to the way you might assess hail damage. Management of Goss's Wilt is difficult. "The best approach to use is hybrid selection," says Robertson. "One thing we are seeing out in the fields is that Goss's Wilt is only occurring with certain corn hybrids that are susceptible to this disease. There are a number of hybrids that have very good resistance to Goss's Wilt. So choosing a hybrid that has good resistance to Goss's Wilt should be your first choice in managing this disease in subsequent years."
Choice of corn hybrid is your number one defense against Goss's Wilt
More information can be found out about Goss's Wilt and other corn diseases on ISU Extension's Integrated Crop Management website.
"This disease is showing up in a number of fields in eastern Iowa this year," says Jim Fawcett, ISU Extension area field agronomist based in Iowa City. "Fungicide applications won't control Goss's Wilt because it is caused by a bacteria, it is not a fungus disease. It causes large lesions, especially on the upper leaves."
Last year a lot of Northern Corn Leaf Blight was misdiagnosed as Goss's Wilt in eastern Iowa, says Fawcett. Both have large lesions and can occur on the upper leaves of corn plants, but Goss's Wilt also will have a lot of black "freckles" along the edge of the lesions, and may also have a greasy or shiny appearance due to the bacterial ooze. "It is more common for Goss's Wilt to show up in fields that suffered some hail damage, or in fields where there was hail damage the last time the field was in corn."