Stem Canker
Stem Canker
Symptoms
Symptoms of stem canker are usually first noticed during the latter half of the growing season. Reddish-brown stem lesions develop during the early reproductive stages of plants. Lesions will usually be in the vicinity of a stem node. A diagnostic symptom of stem canker is that green stem tissue will usually be present both above and below individual stem cankers.
As the disease progresses, cankers will enlarge, longitudinally, turn dark brown to black in color, become slightly sunken and eventually completely girdle stems. At this point, the free flow of nutrients and water is disrupted in the plant. Cankers which coalesce may be confused with stem discoloration caused by Phytophthora. However, stem canker usually forms higher on the plant than does Phytophthora.
Severe stem canker can result in premature, and often sudden, plant death. Foliage of diseased plants initially exhibits interveinal yellowing. This is followed by tissue death between the veins. Eventually, leaves die and usually remain attached to stems.
Cause
Stem canker is caused by the fungus Diaporthe phaseolorum var. caulivora. The fungus normally survives the winter in the seeds, but it will also remain viable in infested crop residue. This is a critical point to note because the infested crop residue may provide enough fungus to create a stem canker epidemic in subsequent soybean crops.
Spores are produced and infections occur during the early vegetative stages of the crop. The disease then goes dormant until the reproductive stages, at which time symptoms are produced. The severity of stem canker is highly dependent on the weather conditions during early crop development. Wet weather favors disease development.
IPM Techniques
- Fields should be check every two weeks from beginning pod fill to harvest maturity for the presence of stem canker.
- At each scouting site, examine two rows of plants ten feet in length for initial signs and symptoms, but be observant over a much wider area for advance symptoms of plant decline.
- The number of sites you will need to check in each field is based on the field size.
- To determine the number of scouting sites see the field size and number of locations chart.
- Plant high-quality, disease-free seed or certified seed.
- Rotate crops, especially where full-season soybeans are grown using no-till or minimum tillage methods.
- Delay planting operations for full season soybeans.
- Plant resistant cultivars.
- Disease is reduced where crops are conventionally tilled.
References and Additional Information
- IPM-3 Kentucky IPM Manual for Soybeans
- PPA-10b Kentucky Plant Disease Management Guide for Soybean by D.E. Hershman, Extension Plant Pathologist
- PPFS-AG-S-7 Stem Canker of Soybeans by Don Hershman and Paul Bachi, Department of Plant Pathology, University of Kentucky
- Compendium of Soybean Diseases, J.B. Sinclair and P. A. Backman (The American Phytopathological Society Press)
