Environmental Factors Seedling diseases tend to be more severe in poorly drained soils. They can, however, present problems in any soil type, especially when high rainfall or cold weather follow planting. Any factor that delays germination and seedling emergence such as poor seed quality, inadequate seedbed preparation, compaction, planting too deep, nematode infestations, and high rates of some herbicides can contribute to the incidence and severity of seedling diseases. Most soybean fields receive one or more herbicides, and most of the available soybean herbicides have the potential to injure soybeans. Some can generate visual symptoms that are similar to disease symptoms.
Soybean tends to be more seriously injured by broadleaf herbicides than grass herbicides.
Pre-emergence herbicides whose label suggests planting soybean below a certain depth probably have the greatest potential to injure soybeans if the herbicide gets into the soybean root zone. Distinguishing between herbicide injury and seedling diseases is frequently difficult. The pattern of where symptoms do and do not appear may give the best indication of whether it is a disease problem or herbicide injury. Symptoms of seedling diseases usually occur in irregular patterns which may correspond to changes in soil type. A disease is more likely to be severe on one plant and show no symptoms on adjacent plants than is herbicide injury.