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CropTalk: On the Lookout: Developing Diseases in Soybeans

August 2021

Published on Sunday, August 1, 2021

CropTalk: On the Lookout: Developing Diseases in Soybeans

As we know all too well, each year of crop production gives us different challenges and opportunities. And as we continue to increase our knowledge and efficiencies of crop production, we continue to be humbled by new pests that rob our fields of yield. Two diseases in particular that have been discovered recently include Red Crown Rot of soybeans and Taproot Decline of soybeans. Both diseases were observed in the early 2000s in the Delta region of the United States. They have since migrated north and have been identified in most soybean growing states of the Midwest.

RED CROWN ROT

Red Crown Rot (RCR), caused by the fungus Calonectria ilicicola, is a soil-borne disease that causes Crown and Root Rot in soybeans. The disease is most prevalent in fields that experience wet conditions near planting. Later in the season, if favorable environmental conditions persist for disease development, the leaves of the soybean plant will exhibit small yellow blotches that eventually lead to interveinal necrosis. Most foliar symptoms will be evident late-season, at R3 or later. Another diagnostic characteristic of RCR is the distinct color and location of the reproductive structure of the disease. Soybeans infected can exhibit red/orange/rust colored reproductive structures called perithecia. Perithecia will be located at the base of the stem, slightly above the soil line. Injury to the roots below the soil line can also be observed. Rotted roots and grey discoloration of the pith will be present in the advanced, later stages of the disease. It is important to remember that RCR can be present in fields without the expression of foliar symptoms. Many of the foliar symptoms consistent with RCR can be like those of soybeans that are infected with Sudden Death Syndrome. In these instances, it is important to actively scout fields to properly identify the pathogen causing the injury. Currently, foliar fungicides are not known to provide protection against RCR. There are a few cultural and management practices that will reduce the possibility of the disease. Delayed planting into warmer soil conditions along with improved field drainage can assist in the reduction of the disease. Also, rotation away from soybeans for two years may help. For those in the peanut growing regions, rotation away from soybeans and peanuts will be beneficial because the pathogen can affect both crops.

 

 

TAPROOT DECLINE

Another recently observed disease in soybean production is Taproot Decline (TRD). Taproot decline is caused by the fungal pathogen Xylaria necrophora. First observed in the mid- 2000s in southern soybean-producing states, TRD has worked its way north into midwestern fields. Much like the aforementioned RCR, TRD is generally seen later in the growing season, but there have been instances where TRD has been found in plants in early vegetative stages. Careful scouting of soybeans must be done to diagnose the disease. TRD first exhibits bronze/ oranging of the leaf surface, which then turns into interveinal necrosis. Foliar symptoms may resemble those of Sudden Death Syndrome, RCR, and a few others. The distinct characteristic separating TDR from the others is the growth of “dead man’s fingers” at the base of the plant or in nearby residue. When the plants are pulled from the soil, the root will easily separate from the stem of the plant. Currently, fungicides are not labeled for the management of TRD in soybeans, but varietal differences are often observed. Although these two diseases are relatively new to most of our marketing area, its more important than ever to get out and scout! Proper identification of disease can help lay the foundation for seed selection and management in future years. If you need scouting assistance or help identifying a disease, please reach out to your local Beck’s representative or field agronomist for help!

For more pest and agronomy articles like this: beckshybrids.com/Agronomy/ Agronomy-Resources

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Jon Skinner
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Jon Skinner

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