Figure 1. Soybean field with plants killed by stem canker that maybe mistaken for early maturity.
Several soybean fields scouted in a number of counties have plants dying or dropping leaves prematurely (Figure 1) and are being mistaken for early senescence. Close examination of these plants indicates that stem canker is causing the premature plant death. Growers are encouraged to scout their soybeans as we are nearing towards soybean maturity in order to determine what could be causing their plants to die prematurely and plan accordingly in subsequent seasons.
Stem Canker Causal Pathogen and Symptoms
Stem canker is caused by fungi, Diaporthe spp. These fungi survive in infested soybean residue and soil and can remain viable for several years. Spores are splashed onto young plants by rain but symptoms do not develop until after flowering. Stem canker symptoms start as small reddish-brown lesions that develop in the lower nodes of the plant. The lesions expand up and down the stem and once they girdle the stem, the plants starts to wilt and eventually the plant is killed (Figure 2). Infected plants occur in patches within a field. Favorable conditions for the disease to develop are continuous surface wetness on the plant (1-4 days of wetness) and a temperature range of 70-85°F.
Figure 2. A close up of a soybean plant with stem canker symptoms.
Stem canker develops later in the growing season; therefore a proactive management decision should be made before planting. Although there are no resistant cultivars against stem canker in the northern region, tolerance differences exist among cultivars for this disease. Residue management through rotation and residue incorporation into the soil can help reduce the inoculum.