Initial symptoms appear as small reddish-brown lesions at the base of branches and leaf petioles in the lower part of the plant. The lesions later extend up and down the stem and turn dark-brown. The alternate pattern of green and brown patches along the stem characterizes the disease. The canker damages the internal tissues of the stem and hinders the transport of water and nutrients. Interveinal chlorosis appears on leaves. The leaves might die later but remain attached to the stem. Plant parts above the lesions may die and podding is severely compromised.
Soybean stem canker is caused by the soilborne fungus Diaporthe phaseolorum. There are two slightly different variants of the fungus causing southern and northern stem cankers. It overwinters in infested crop residues or on seeds.It infects plants early in the vegetative stage but symptoms become apparent only during the reproductive stage. Persistent wet and rainy weather conditions, in particular early in the season, favor the infection. Poor tillage practices might be favorable, too.
If available, an integrated approach with biological fungicides is recommended.
Always consider an integrated approach with preventive measures together with biological treatments if available. Fungicide treatments may help to control the infection but results differ widely depending on time of application, environmental conditions and products used. If necessary, apply products containing mefenoxam, chlorothalonil, thiophanate-methyl or azoxystrobin during vegetative and reproductive growth stages