By Nathan Mueller
Figure 1. Stunting, discoloration, damping off, and root rot are all common symptoms of seedling diseases, like the plant on the left compared to the healthy plant (right).
Cool wet soil conditions from repeated rainfall events across Nebraska can likely be to blame for development of some seedling diseases in corn. A number of different pathogens can cause similar symptoms, negatively impacting plant health and potentially reducing plant stands. This week seedling diseases were documented in 10% of surveyed fields in Dodge County in eastern Nebraska, mostly in corn-after-corn fields in river valleys. Be sure to monitor seedling emergence and stand establishment across the state during the coming weeks so that if problems occur they can be detected as early as possible.
Figure 2. Field scouting is recommended to assess inconsistent corn stands and look for symptoms of seedling diseases.
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 their symptoms are very similar. Sometimes, diagnosis may be of limited value because management is often the same for several seedling diseases. Microscopic examination and other laboratory analyses of the diseased seedlings can often identify the cause(s) of the problems. In addition seedling diseases can be confused with insect injury, herbicide damage, planting problems, or environmental stresses that often have similar symptoms.
Symptoms of seedling diseases include:
- Rotted seed prior to germination
- Rotted or discolored seedlings after germination prior to emergence
- Post-emergence seedling damping off (Figures 1-3)
- Root or hypocotyl decay
At least 14 species of Pythium can cause seedling blight and root rot. These pathogens require excessive moisture because they produce motile swimming zoospores that infect plant roots. Thus, wet soil conditions are most favorable for Pythium root rot. 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.
Management
Unfortunately, resistance is not available for seedling diseases in corn. Improved field drainage can help reduce the incidence and severity of some seedling diseases and delaying planting until soil conditions are warmer will promote rapid seed germination and emergence. The most common method for disease management is the use of seed treatment fungicides on almost all seed corn.
Figure 3. Root rot and pre- or post-emergent damping off of seedlings (eft) are commonly caused by seedling diseases during wet conditions and can lead to stand loss.
Crop rotation can provide some reduction in disease, but some pathogens also may infect soybean and other crops.
Most seed corn is 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, but, in spite of their activity, diseases may still develop, such as during extended periods of inclement weather or severe pathogen pressure.
Some fungicides now also are labeled for application in-furrow at planting. Use of fungicides in-furrow at planting may provide some additional protection against these pathogens in fields with severe pathogen pressure and chronic seedling diseases, but more research needs to be conducted to better predict their potential benefits and economic return.
Seed treatment fungicides 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.