Towards a Successful Harvest: Stalk Rots and Standability Issues

September 13, 2010
ICM News

By Alison Robertson, Department of Plant Pathology

It's hard to believe the growing season is almost over. Most of the corn across the state is nearing or at black-layer, which means it is time to scout fields for stalk rots in an effort to evaluate standability and plan a successful harvest.

Stalk rots are likely to be an issue this growing season. We have seen significant blighting of the leaves in the upper canopy predominantly from Goss's wilt, northern corn leaf blight, gray leaf spot and anthracnose top dieback. When significant leaf blight occurs in the upper canopy, the risk of stalk rots increases. Furthermore, overcast conditions, such as we had throughout most of the grain filling period, favor stalk rot development. Since stalk rots reduce standability, fields in which greater than ten percent of plants are affected by stalk rots, should be scheduled for an early harvest. 

In Iowa this year, we have had reports of bacterial, anthracnose, Fusarium and Diplodia stalk rots. Incidence (percent infected plants) ranges from field to field and is likely a function of genetics. It's a good idea to identify what stalk rot is predominant in the field to help with hybrid selection in subsequent years.

While all stalk rots result in rotting and shredding of the pith tissue, they each have their own identifying characteristics.

Bacterial stalk rot

This stalk rot rarely occurs in Iowa, however this year we have had several reports of the disease from across the state. Bacterial stalk rot is favored by high temperatures, high relative humidity and heavy rainfall or irrigation. The most characteristic symptom of this stalk rot is the foul odor when you spilt the stalk. 

Anthracnose stalk rot

Dark streaks on the outside of the stem are characteristic of this stalk rot (Fig. 1, below). 

Fusarium stalk rot

No discoloration occurs on the outside of the stalk, but the nodes may appear white due to growth of the fungus on the outside of the stalk. A pink discoloration (Fig. 2, below) may be seen in the pith of infected plants when the stalks are split open. Sometimes Fusarium stalk rot may be confused with Gibberella stalk rot (because of the pink pith tissue) or with Diplodia stalk rot, however no black specks can be found on the outside of the stalk tissue.

Diplodia stalk rot

The identifying characteristic of Diplodia stalk rot are tiny black specks (pycnidia) buried in the outer rind of the stalk at the lower nodes (Fig. 3, below). Diplodia may be mistaken for Gibberella stalk rot because of the black specks; however, the black specks associated with Gibberella stalk rot can be easily scraped off with a thumb nail. Furthermore, the pith tissues of Gibberella stalk rot are often discolored pink to red.

Scouting Tips

• Target fields that have had significant foliar disease.

• Target hybrids with low stalk rot and/or standability scores.

• Evaluate at least 100 plants per field (20 plants in 5 locations).

• Use the "push test" or the "pinch test" to determine standability. If 10 to 15 percent of plants lodge or are rotted, schedule an early harvest.

anthracnose stalk rot

Figure 1.  Black blotches and streaks on the outside of the corn stalk are diagnostic for anthracnose stalk rot.


fusarium stalk rot

Figure 2.  Light pink discoloration of the pith tissues may be evident with Fusarium stalk rot.

diplodia stalk rot

Figure 3.  Pycnidia (tiny black fruiting bodies) buried in the rind at the lower internodes are diagnostic for Diplodia stalk rot.

Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be reached at (515) 294-6708 or by email at

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 September 13, 2010. 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...