Extensive losses from the disease have been reported in some years. While this fungus also attacks pods and causes purple seed stain, there is no consistent relationship between the occurrence of leaf spot and purple seed stain. Symptoms are first observed at the beginning of seed set. This discoloration may extend to the upper stems, petioles, and pods. Heavily infected leaves rapidly turn yellow and fall, mimicking senescence.
Lower leaves remain green.
Although some cultivars possess resistance, control is primarily achieved by application of foliar fungicides starting at early pod set. Alternaria leaf spot has been reported from all soybean growing areas. This fungus is often a secondary invader following mechanical injury, insect damage, or another disease. Altemaria leaf spot is a late season disease that developsonmaturingleavesor on younger leaves if injured. If uninjured, most improved determinate cultivars appear to be resistant until leaves start to senesce.