April 2, 2010

Spring can be a stressful time for producers preparing to plant corn and other crops, particularly following a delayed and stressful harvest that still hasn’t ended for some. For those fortunate enough to be caught up on field work and thinking ahead to planting, there are a lot of things to consider.

Planting early to get ahead of schedule may be appealing, but can lead to stressed seedlings and the development of seedling diseases and thin stands if soil conditions are less than optimal. In particular, cool (especially less than 50ºF) and/or wet conditions are especially conducive to the development of several seedling diseases.

Common Seedling Diseases

Figure 1. Rotted corn seedling. Figure 2. Post-emergence seedling corn damping off.  (Note seedling on the left compared to the other two apparently healthy seedling plants).

Seedling diseases can be caused by any of several common soil-borne organisms, such as Pythium, Fusarium, Rhizoctonia or plant parasitic nematodes. Seedling diseases have similar symptoms, often making diagnosis difficult. 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 are often necessary to identify the cause of the problem and differentiate damage from disease, insect injury, herbicide damage, planting problems, or environmental stresses that often have similar symptoms.

• Symptoms of seedling disease include:
• Rotted seed prior to germination
• Rotted or discolored seedlings after germination prior to emergence (Figure 1)
• Post-emergence seedling damping off (Figure 2)
• Root decay

Almost all seed corn is treated with more than one seed treatment fungicide, often an insecticide, and, this year, sometimes an optional 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 under severe pathogen pressure. You can minimize the likelihood of developing seedling diseases by planting high quality corn seed at appropriate planting depths and soil conditions.

Tamra Jackson
Extension Plant Pathologist