Plant Disease: Stem Canker

Taxonomy:

Cause:

• The fungus normally survives the winter in the seeds, but it will also remain viable in infested crop residue.


• 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.


• The severity of stem canker is highly dependent on the weather conditions during early crop development.


• Wet weather favors disease development.

Symptoms and Identification:

• Stem canker is 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.

Management:

• 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.