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Green Stem and Stem Canker: Emerging Soybean Diseases in Illinois

Glen Hartman Glen Hartman
Associate Professor
Dept. of Crop Sciences, USDA/ARS
(217) 244-3258; ghartman@illinois.edu
Wayne Pedersen
  Wayne Pedersen
Associate Professor
Department of Crop Sciences
(217) 333-3847; wpederse@illinois.edu
 

A number of soybean diseases such as soybean cyst nematode, sudden death syndrome, and white mold are found in at least some soybean fields in Illinois every year. Less commonly found, however, are green stem and stem canker. Although neither of these diseases is new, they are cyclical and, like all diseases, are affected by environmental factors.

Green Stem
Figure 1. Green Stem.

Both green stem and stem canker were observed more frequently in 1999 than in the past few years. This prompted the support of the Illinois Soybean Check-off Board (ISCB), starting in the summer season of 2000, to fund research for both of these diseases to determine their occurrence in the state, evaluate varieties for resistance, and investigate other potential management strategies.

Green stem (Figure 1) appears to be a stress-related disease of soybeans that lowers seed quality and yields. In addition, the presence of significant numbers of green-stem affected plants in fields can delay harvest. Young leaves in the upper canopy may exhibit green to yellow mottling.

A virus called bean pod mottle virus (BPMV) has been found associated with green stem. BPMV is beetle-transmitted to soybean and causes a mottling of soybean leaves. This virus was first noted on soybeans in 1958. The occurrence of this virus has been documented in Illinois, but the distribution throughout the state is not known.

Our research group will conduct a statewide survey to assess the distribution of BPMV and its occurrence in seeds. In addition, insect pests, including bean leaf beetles and corn rootworm beetles, will be collected in or near fields with green stem to determine their role in the spread of this virus.

Stem Cankers
Figure 2. Stem Cankers.

Phomopsis seed decay, pod and stem blight, and stem canker (Figure 2) are three diseases caused by related fungi. There are two types of cankers caused by related organisms. One causes northern (DPC) and the other southern (DPS) stem canker. Both pathogens are capable of killing full-grown plants from midseason to maturity.

In 1999, there was a resurgence of stem canker in Illinois and neighboring states. Symptoms of stem canker include discoloration of leaves and stems. The first symptoms occur during flowering as small, reddish brown lesions, usually near a lower leaf node. As the season progresses, the lesions expand longitudinally to form cankers. Severe damage depends on the amount of early infection associated with extended periods of rainy, wet weather.

Our research group will characterize the isolates that caused stem canker in 1999 and compare them to isolates in the 2000 season, and we will develop inoculation techniques to evaluate soybean varieties for resistance.

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