By Alison Robertson, Department of Plant Pathology and Laura Jesse, Plant and Insect Diagnostic Clinic
This past week several corn samples infected with Goss’s wilt were submitted to the Iowa State University Plant and Insect Diagnostic Clinic. Tamra Jackson at University of Nebraska, Lincoln has also reported an increase in the prevalence of Goss’s wilt in Nebraska this growing season (see Crop Watch, August 8, 2008).
Goss’s wilt was first reported on corn in Nebraska nearly 40 years ago; since then it has been reported across the entire Corn Belt. The disease is caused by the bacterium Clavibacter michiganense subsp. nebraskensis. Hosts of the bacterium include corn, green foxtail, barnyard grass and shattercane. The bacterium overwinters on crop debris and in and on corn kernels. Corn plants are susceptible at all growth stages, with optimum temperatures for disease development at 80 degrees Fahrenheit. Infection of leaves, stems and roots occurs primarily through wounds caused by sandblasting, hail, heavy rain or wind.
Symptoms of Goss’s wilt being reported in Iowa are leaf blight of the leaves at the top of corn plants causing growers to worry about anthracnose top dieback. The disease may also be misdiagnosed as Northern leaf blight or Stewart’s disease. Careful examination of the affected leaves reveals large grey to reddish or yellow lesions that extend down the leaf veins (Figure 1).
Dark green to black “freckles” are evident within the lesions (Figure 2) and are diagnostic of the disease. Often the diseased tissue appears shiny due to bacterial exudate that has dried on the leaves. The bacterium may also infect the xylem (water-conducting) tissues of the plant and result in wilting and death of the plants. If you would like confirmation of Goss’s wilt please submit samples to the ISU Plant and Insect Diagnostic Clinic.
There is nothing that can be done this growing season to manage Goss’s wilt. Fungicides are not effective against this bacterial disease. Partially resistant hybrids remain the most effective management tool for this disease, so check with a seed dealer for hybrids that have resistance to Goss’s wilt. In fields where Goss’s wilt has been a problem, planting a partially resistant hybrid is recommended. Weed management, rotation to non-host crops and tillage to bury infested crop residue are also helpful.
For additional resources please see, Goss’s bacterial wilt and leaf blight of corn.
Figure 1. Large grey to reddish or yellow lesions that extend down the leaf veins resulting in extensive leaf blight. Robertson 2008.
Figure 2. Dark green to black “freckles” are diagnostic for Goss’s wilt. Robertson
Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic.