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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Observed under magnification, tiny, black fungal survival structures called microsclerotia can help in diagnosing charcoal rot.
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Tillage and continuous soybean production favor charcoal rot at the NWIARDC

Last week's blog post was about several soybean diseases that have been recently observed in Western Illinois. Another disease that may be affecting soybeans in Western Illinois is called charcoal rot.

The fungus (Macrophomina phaseolina) that causes charcoal rot can cause disease in many different plants including many grass and broadleaf weeds, corn and soybean. Charcoal rot is favored by high soil temperatures and dry soil conditions during reproductive growth stages. These conditions increase plant stress which can allow the pathogen to proliferate in previously infected plants, causing disease symptoms and yield loss.

The disease charcoal rot gets its name from tiny, black survival structures of the fungus called microsclerotia that resemble charcoal dust particles. These microsclerotia can be observed if one carefully scrapes away the outer epidermis tissue of the lower stem (Figure). Microsclerotia form throughout lower stem and taproot tissue, causing this tissue to appear greyish with the naked eye (Figure). One can better observe microsclerotia under a microscope or a magnifying glass (Figure).

Symptoms of charcoal rot include wilted plants (with leaves remaining attached to the plant) and premature maturation. It is the signs of the pathogen, the charcoal dust-like microsclerotia that can help in distinguishing charcoal rot from other soybean stem and root diseases.

Crop rotation, tillage and charcoal rot

In a long-term tillage and rotation study at the Northwestern Illinois Agricultural Research and Demonstration Center (NWIARDC) many soybean plants wilted and died prematurely from charcoal rot (Figure). After a little bit of detective work, it became evident that the diseased soybeans had a couple of things in common: they were grown under continuous soybean production (more than 15 years) and were grown in soil that had been tilled (chisel plowed in fall and worked with a soil finisher in spring).

Fifteen years of data from this study collected by NWIARDC personnel under the direction of University of Illinois Agronomist, Dr. Emerson Nafziger, reveals that soybeans under tilled, continuous soybean production yield less than any other tillage and crop rotation combination. Additionally, continuous soybeans tend to yield less when grown in tilled soil than in no-till production.

One can theorize about why charcoal rot was prevalent in these plots in a growing year like 2013. This year, dry conditions prevailed throughout the majority of the growing season, leading to high soil temperatures and moderate drought conditions which favor disease. Any soil moisture that may have been retained under no-till production is lost through tillage, further stressing the soybeans. Additionally, continuous soybean production also favors the build-up of higher soil populations of the soybean cyst nematode (SCN). SCN and other soybean root pathogens can reduce root function, which can further stress water-stressed plants.

Additional information about charcoal rot can be found at the Plant Health Initiative website. Content of this website is provided by University researchers from 12 Midwestern states and is sponsored by the North Central Soybean Research Program through soybean check-off dollars.

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