How to identify seedling diseases . When seed fails to emerge because of fungal attack, it is called seed rot or preemergence damping-off. The causal fungi cannot be determined without aboveground symptoms. Pythium damping-off will be the first seedling disease to occur in the growing season because this fungus prefers cold soil temperatures. Dead seedlings may be visible on the ground with infected plants killed before the true leaf stage.
Plants often have a rotted appearance.
Leaves of infected seedlings first will be gray-green and then turn brown. A few days later, the plants will die. Diseased plants are easily pulled from the soil because of rotted roots. If symptoms similar to those caused by Pythium occur when soil temperatures are warm or in late-planted soybean, the disease is more likely caused by Phytophthora . Another way to determine the causal fungus is to check for stem rot.