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Figure 1. Identifying characteristics for Goss’s wilt. (A) leaf “freckles65533;? on a plant symptomatic for Goss’s wilt (right) appear similar to saprophytic fungal growth (left). (B) bacterial ooze. (C) freckles appear luminous when held up to block the sun.
Goss’s wilt, a persistent and economically significant disease of corn, is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis. The disease occurs as either a vascular wilt or leaf blight. Systemic infection that occurs early in the season results in a vascular wilt. Leaf blight symptoms (Figure 1) usually appear mid-season as long, gray-green to black, water-soaked streaks extending along leaf veins. Small, dark, water-soaked flecks, referred to as “freckles65533;?, often occur inside larger lesions and at the edges of lesions where symptoms are advancing. Leaf freckles are luminous when lighted from behind, such as when the sun is used as backlighting. Bacterial cells may ooze from infected leaves and dry on leaf surfaces forming a shellac-like sheen. As lesions mature, large areas of tan to brown dead leaf tissues are apparent.
The pathogen overwinters in crop residue. Infection commonly occurs following severe weather that creates leaf wounds through which the bacteria can enter the plant.
Figure 2. Symptoms of Goss’s wilt can be confused with other causes of leaf necrosis.
Goss’s wilt symptoms can be confused with other causes of leaf necrosis such as: drought, heat stress, nutrient deficiency, northern corn leaf blight and Stewart’s wilt (Figure 2). Growth of saprophytic fungi on dead leaf tissue may appear similar to the freckles associated with Goss’s wilt (Figure 1).
Symptomatic leaf tissue should be examined by a plant disease clinic for diagnosis and proper management of Goss’s wilt in future plantings. In a plant diagnostic laboratory, samples may be evaluated for the following:
Many universities have plant disease clinics that can diagnose Goss’s wilt. Though many clinics will accept plant samples from both local and out-of-state sources, it may be advantageous to use an in-state plant clinic as out-of-state fees are sometimes higher, shipping times may be longer, and concerns about the introduction of invasive insects and diseases may necessitate special handling.
Several university plant clinics are listed below; this is not a complete list. Check with your local university Extension office for the nearest clinic.
Samples should be accompanied by completed forms for the specific clinic and the required fees for the service. Provide any other information that may be useful for diagnosis, including any other factors that may have caused symptoms similar to Goss’s wilt.
For more information about Goss's Wilt read the Goss's Wilt Quick Facts
Jackson, T. 2007. Goss’s bacterial wilt and leaf blight. Plant Disease Central. University of Nebraska. http://pdc.unl.edu. Corn disease management. 2002. Illinois Agronomy Handbook, 23rd edition. University of Illinois Extension. Web sources verified 6/12/15. 130808060435