Seedling Diseases Appearing in Corn
Cool soil temperatures and episodes of rainfall are contributing to the development of seedling diseases in corn this spring. The most common seedling diseases that have been identified in samples submitted to the UNL Plant and Pest Diagnostic Clinic are those caused by Pythium and less frequently, Fusarium species.
Seedling diseases can be caused by any of several common soilborne organisms, such as Pythium, Fusarium, Rhizoctonia, or plant parasitic nematodes. Seedling diseases are often difficult to diagnose because they have similar symptoms. Diagnosis of a specific disease may be of limited value because management may be similar for several seedling diseases. Microscopic examination and other laboratory analyses of the diseased seedlings often can identify the cause(s) of the problems.
Seedling diseases can be confused with insect injury, herbicide damage, planting problems, or environmental stresses that often have similar symptoms. Possible symptoms of seedling diseases include:
- Rotted seed prior to germination
- Rotted or discolored seedlings after germination prior to emergence
- Postemergence seedling damping off (Figures 1-3)
- Root decay
At least 14 species of Pythium have been previously identified that can cause seedling blight and root rot. These pathogens require excessive moisture because they produce motile swimming zoospores that infect plant roots. The pathogen overwinters in soil and infected plant debris by producing thick-walled oospores that can survive for several years in the absence of a suitable host of favorable weather conditions.
Although uncommon, Pythium also may cause stalk rot disease in corn during extended periods of wetness during the middle and later portions of the growing season. Symptoms of Pythium stalk rot can cause collapse of the lower stalks at or near the soil surface. Stalks may appear collapsed, twisted, and water-soaked and could be confused with bacterial stalk rot, except that they lack the characteristic foul odor.
There are more than six Fusarium species that can cause seedling diseases and root rots, several of which are common in Nebraska fields. Stressed plants due to weather extremes (temperature and moisture), herbicide damage, and physical injury are more prone to infection and disease caused by Fusarium species.
Unfortunately, resistance is not available for diseases caused by Pythium and Fusarium. Although improved field drainage can help reduce seedling disease severity, the most common method for disease management is with the use of seed treatment fungicides. Crop rotation also can provide some reduction in disease.
Most seed corn is already treated with more than one seed treatment fungicide, often an insecticide, and sometimes a nematicide. These products can provide protection against some of the pathogens that cause seedling diseases. Diseases may still develop, however, in spite of their activity, such as during extended periods of inclement weather or under severe pathogen pressure. Seed treatments will only provide protection during the first few weeks immediately after planting.
You can minimize the likelihood of developing seedling diseases by planting high quality seed at appropriate planting depths and soil conditions to support rapid plant growth and emergence.
Plant Disease Diagnosis
For information on submitting samples to UNL's Plant and Pest Diagnostic Clinic for diagnosis, see this May 24 CropWatch article.
Extension Plant Pathologist
Coordinator, UNL Plant and Pest Diagnostic Clinic