Diseases have been common this year in Nebraska corn fields. Producers and crop consultants should continue to scout to monitor for development of stalk rots.
Stalk Rot Diseases
Figure 1. (Left) Anthracnose stalk rot can cause the development of black lesions visible on the outside of the stalk.Figure 2. (Below) Fusarium stalk rot can be evident as white fungal growth at the nodes of affected plants.Figure 3. The stalks of plants with Fusarium stalk rot may eventually turn pink to salmon in color.
Stalk rots are becoming evident in some corn fields across the state. Excessive rain and flooding early in the season led to nitrogen leaching and deficiencies and the development of foliar diseases. These conditions early in the season can be expected to put some fields at increased risk for stalk rot development now.
The first indication of rotted stalks may be the rapid and premature desiccation of some plants in the field. These plants often have stalks that are hollow and easily crushed by hand or bent using the “push or pinch” test. Stalk rots can occur at any point in the stalk from the crown at/below the soil line all the way to the tassel. Rotting that occurs at an upper node and kills only the upper plant parts is referred to as “top rot” and does not necessarily cause plant lodging.
Harvest Adjustments
There is nothing to be done at this point in the season to stop stalk rots. But, they can impact harvestability if plants lodge prior to harvest. Consider harvesting those fields that have a high incidence of stalk rots early or first to avoid losses after lodging. The costs required to dry grain harvested early from a field with severe stalk rot may be less than that of the additional costs that will be required to harvest a field of downed corn.
Identifying the Problem
IThere are several fungi and bacteria that are common in our production fields that can cause stalk rot diseases. Some of the most common in samples submitted to the UNL Plant and Pest Diagnostic Clinic this year are listed below.
Anthracnose stalk rot can also cause a leaf disease and is a common cause of top rots in corn. In more advanced stages the disease can cause the development of black lesions visible on the outside of the stalk (Figure 1).
Fusarium stalk rot is especially common during damp conditions and may lead to white fungal growth visible at the nodes (Figure 2). Eventually, the disease may cause discoloration of the inside of stalks to pink or salmon (Figure 3).
Bacterial stalk rot tends to occur mid season, but this year it has developed lately in some Nebraska fields that were flooded earlier in the season. The most diagnostic feature of this disease is the very foul odor it causes. Plants that develop the disease late in the season are sturdy enough that they do not typically collapse like those infected earlier in the season.
If you are in doubt about the identity of a disease or cause of another plant problem, you may submit a sample to the UNL Plant and Pest Diagnostic Clinic (P&PDC) for diagnosis. For more information about these and other plant diseases or for submission instructions and forms, visit the Plant Disease Management section of CropWatch.
Tamra A. Jackson Extension Plant Pathologist, Lincoln Amy (Ziems) Timmerman UNL Plant and Pest Diagnostic Clinic Coordinator, Lincoln
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