Tips for Diagnosing Goss's Wilt and Leaf Blight

June 28, 2012
ICM News

By Alison Robertson, Department of Plant Pathology and Microbiology


In the past 5 years, Goss’s wilt and leaf blight has become increasingly prevalent in Iowa. This growing season, the disease has already been reported from several fields. Consequently many agronomists and scouts have been checking fields and some agronomists have been making use of the immunostrip test from AgDia.


What symptoms should you be looking for?

Freckles! Dark spots that resemble freckles and occur in the outside edge of a developing lesion are the most characteristic symptom of Goss’s (Figure 1).

Figure 1. Freckles are diagnostic for Goss's wilt and leaf blight.


If you see freckles, you can be confident you’re looking at this disease. Freckles may be confused with black colonies of saprophytic fungi that colonize dead leaf tissue. A neat trick we have learned is that if you hold a suspected lesion to the light, freckles appear transparent (Figure 2), while colonies of saprophytic fungi are dark (Figure 3). On systemically infected wilted plants, freckles are also evident on the leaves.

Figure 2. When backlit, freckles appear transparent.


Figure 3. Colonies of saprophytic fungi remain dark when backlit.


Other characteristics of Goss’s leaf blight are very large red to grey lesions that usually start from the leaf tip or leaf margins and extend down the leaf (Figure 4). The lesions are usually a blend of dead tissue, grey-green water soaked tissue and yellowed tissue. You may also notice the lesions are sticky and have shiny patches on the surface. This is the Goss’s bacterium that has oozed out of the diseased tissue and dried on the surface of the leaf.

Figure 4. Lesions of Goss's leaf blight are large and usually start from the leaf tip and extend downward.


What if I get a positive with an immunostrip test?

The immunostrip test is a useful test to confirm Goss’s, but it must be used carefully. The test does give false positives. We know, for example, that purple leaf sheath (Figure 5) will give a positive with the strip test from AgDia. Purple blotches on the leaf sheath of corn plants are not disease, but are caused by saprophytic organisms feeding on dust, pollen, etc., that has collected behind the leaf sheath.

Figure 5. Characteristic symptoms of purple leaf sheath.


Other tips

Other evidence to consider for a positive Goss’s diagnosis in addition to the leaf symptoms and the immunostrip test include:

•Hybrid – Is the hybrid rated susceptible to Goss’s?

•Field – Does the field have a history of Goss’s ? Was corn grown in the field in the previous year and is surface residue present?

•Weather – Has severe weather occurred in the area within the past few weeks?

As with all diseases, correct diagnosis is important to enable appropriate management practices to be followed. For Goss’s, tolerant hybrids is by far the best management tool we have at present. There are numerous foliar applied products being marketed for Goss’s management. Several field trials are being done here in Iowa, and also neighboring states, to evaluate the efficacy of these products.


Alison Robertson is an associate professor of plant pathology and microbiology with extension and research responsibilities. You can reach her at 515-294-6708 or e-mail

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on June 28, 2012. The information contained within may not be the most current and accurate depending on when it is accessed.


Alison Robertson Professor of Plant Pathology and Microbiology

Dr. Alison Robertson is a professor of plant pathology and microbiology. She provides extension education on the diagnosis and management of corn and soybean diseases. Her research interests include Pythium seedling disease of corn and soybean and Goss's wilt. Dr. Robertson received her bach...