Goss’s wilt of corn, caused by the bacterium Clavibacter michiganensis subsp. nebraskensis, has been confirmed in several fields in northeast Indiana in 2015, making these the most eastern confirmations of the disease in the state to date. The disease has also been detected in northwest Indiana this year.
The bacterium that causes the disease survives in residue and some grassy weed species and infects corn plants through wounds. The diagnostic symptoms of Goss’s wilt include water-soaked lesions that have black “freckles” or specks on or surrounding the lesions. These lesions can be on any leaves of the plant and may be quite large on susceptible hybrids, often causing a scorched leaf symptom from the tip to the base of leaves. Bacteria can also move onto the leaf surface and give the leaves a shiny appearance.
These lesions are very easy to confuse with the leaf burning and firing that is common across Indiana due to nitrogen deficiency and plant stress. Goss’s wilt foliar lesions may also be easily confused with the fungal disease northern corn leaf blight.
It is important to remember that this disease MUST be diagnosed with at least two methods: microscopic observation of bacterial streaming from symptomatic tissue, and confirmation of the causal bacteria using organism-specific tests. In-field testing is possible with an immunostrip test marketed by the company AgDia (http://www.agdia.com/). However, there are limitations to these strips, and it is not recommended to rely solely on a diagnosis based on these strips. Sample contamination can occur in the field, and strips may occasionally detect the bacterium that causes Goss’s wilt when it is not actually present in the plant. Because of the potential for these false positives, it is important that any sample that tests positive in the field for Goss’s wilt be sent to a diagnostic lab for additional microscopic observation. (www.ppdl.purdue.edu) Plants that are not infected with the bacterium will not exhibit this bacterial streaming, and Goss’s wilt can be ruled out.
It is important to scout fields in these areas to determine if fields are affected by Goss’s wilt because this disease must be managed preventatively. Fields that are affected by Goss’s wilt should be planted to a resistant hybrid in future years.
Other management options include tillage and rotation to help reduce the bacteria population present in the field for the subsequent corn crop. Residue can harbor bacteria for years. In-season management is limited and may not be warranted depending on the growth stage and yield potential of the crop. Fungicides are not recommended to use for management of Goss’s wilt since it is a bacterial disease.