By Alison Robertson, Department of Plant Pathology and Microbiology
On June 24, we visited a grower's field in Carroll County where we have a research study on Goss's wilt of corn. The field has been in corn for several years and has a history of Goss's wilt. The field was planted May 5 and was at growth stage V6 to V7. We found plants with typical symptoms of the leaf blight (Figure 1) and also the wilting stage of the disease. This is the earliest report of Goss's wilt in Iowa that I am aware of. It is also the first time I have seen the wilting stage of the disease in this state.
Typical lesions of Goss' wilt were characteristic of approximately one percent of the plants in the field. Long, dark brown to grey-green lesions were evident on the edge of the leaves or along folds in the leaf. Freckles, which are diagnostic for Goss's, were present. On some plants, only one leaf was affected, while on other plants, all leaves were affected (Figure 2). We also noticed some plants that were wilted. Closer examination of the plants revealed subtle lesions. When the stalk of the plant was cut, the vascular system of the plant was discolored orange-brown (Figure 3). In this case, infection of the plant by the bacterium was systemic. In other words, the bacterium was present in and plugging the vascular system of the plant.
There are no rescue treatments for Goss's wilt. The disease is caused by the bacterium Clavibacter michiganenisis subsp. nebraskaenesis. Fungicides are not effective. Management recommendations include planting resistant hybrids, rotation to a non-host crop and residue management.
Figure 1. Typical Goss's wilt leaf lesions. Note the "freckles" in the infected tissue. A. Robertson
Figure 2. Young corn plant with symptoms of Goss's wilt. A. Robertson
Figure 3. Discolored vascular tissue of a young corn plant infected the bacterium that causes Goss's wilt. W. Beck
Alison Robertson is an assistant professor in the Department of Plant Pathology and Microbiology with extension and research responsibilities; contact at email@example.com or phone 515-294-6708.