Soybean Seedling Diseases

Preventing Soybean Seedling Diseases

The first form of prevention in soybean seedling diseases is to avoid using poor quality seed. Use only high quality seed that isn’t contaminated with fungal pathogens. This will help prevent low germination and increase seedling vigor.

Other factors that could lead to seedling diseases include: inadequate seedbed preparation, compaction, planting too deep, nematode infestations, and high rates of some herbicides.

Scouting, Identifying Seedling Diseases

If scouting reveals stand reduction, it’s important to determine if the cause was a fungal pathogen. Different pathogens are present under different field conditions. The following information can help distinguish which pathogen may be present in your field: general soil temperatures, general soil moisture (saturated, wet or dry), variety resistance or tolerance to Phytophthora, and plant growth stage.

There are three main categories of seedling diseases:

Seed rot occurs during the VO-VE growth stages and may be caused by three pathogens; Pythium, Phytophthora, and Phomopsis. Determining which pathogen caused the seed rot can be difficult. Typical symptoms are soft decay of seed, missing seedlings in the row or poor emergence.

Seedling Mortality (damping-off or seedling blight) occurs during the VE-V4 growth stages. Pythium, Phytophthora, and Rhizoctonia, can cause seedling mortality.

Root or lower stem decay may take place during the seedling stage or may not be apparent until later reproductive stages (VE-Rn). Pathogens that cause root stem decay during the seedling stage are the same as those that cause seedling mortality (above).

Finally, seedling disease symptoms may be confused with herbicide damage, effects of low pH, or other seedling disorders. To help ensure you have a seedling disease problem versus herbicide damage, consider the following: seedling diseases usually occur in irregular patterns that may correspond to changes in soil type. Herbicide damage typically follows a pattern related to the equipment and a group of adjacent plants will be affected.

Source: Monsanto Agronomic Spotlight, photos courtesy of Iowa State University Extension and University of Minnesota extension

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