Wet field conditions from recent rainfall events across Nebraska may put early planted corn at added risk for seedling diseases. Cool soil temperatures and episodes of recent rainfall are especially favorable for some of the most common and damaging seedling diseases. Be sure to monitor seedling emergence and stand establishment in the coming weeks so that if problems occur they can be detected as early as possible.
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. Seedling diseases can be confused with insect injury, herbicide damage, planting problems, or environmental stresses that often have similar symptoms.
Seedling disease symptoms include:
- Rotted seed prior to germination
- Rotted or discolored seedlings after germination prior to emergence
- Post-emergence seedling damping off (Figure 1)
- Root or hypocotyl decay
At least 14 species of Pythium have been identified that 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 across much of Nebraska. The pathogen overwinters in soil and infected plant debris by producing thick-walled oospores that can survive for several years in the absence of favorable weather conditions.
Management
Tamra Jackson-Ziems discusses corn seedling diseases on the April 15 Market Journal.
Unfortunately, resistance is not available for seedling diseases in corn. Improved field drainage can help reduce the incidence and severity of some seedling diseases, as well as delaying planting until soil conditions are warmer and will promote rapid seed germination and emergence. The most common method for disease management is seed treatment fungicides now applied to almost all seed corn.
Crop rotation can reduce seedling diseases to some extent; however, some of these diseases may also infect soybean and other crops.
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. In spite of their activity, diseases may still develop, such as during extended periods of inclement weather or under severe pathogen pressure.
Some fungicides now also are labeled for application in-furrow at planting. Use of fungicides in-furrow at planting may provide 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.
