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Iron Deficiency Chlorosis (06/25/20)

Iron deficiency chlorosis (IDC) is appearing in soybean fields this time of the year.

Iron deficiency chlorosis (IDC) is appearing in soybeanplsc.1 fields this time of the year. There is normally enough iron (Fe) available in the soil; however, young soybean plants may not be able to take up enough Fe if soil pH is alkaline. The cotyledon and unifoliate leaves of soybeans emerge green, as they can utilize the iron present in the seed, but as the trifoliate leaves start to develop the physiology of the plant changes and iron cannot move from one area of the plant to another anymore. This is when chlorosis often starts to appear (Photo 1). The IDC symptoms appear as yellowing leaf tissue between the veins while the veins may remain green.

Severe IDC cases may turn leaf tissue brown and cause necrosis. Plants with chlorosis are often stunted and behind in growth and development compared to healthy plants. Chlorosis is common when soybean plants are grown on high pH calcareous soils. Elevated soil salts result in greater plant stress and more severe IDC. Under certain conditions such as excess moisture, cool temperatures and/or high soil nitrate content, IDC symptoms can be even more severe. A description about the need for Fe in soybean and why IDC develops in the plan, can be found in the soybean fertility Extension publication’s section about iron (see SF1164).

Soybean plants may grow out of the chlorosis and become green again, however yields might already be reduced due to IDC. In a 2019 trial near Erie, ND, IDC scores were recorded during the season and yield was obtained. When IDC was more pronounced (higher IDC score) a lower yield was the result (Graph 1).
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Soybean varieties have genetic differences for tolerance and susceptibility to IDC symptoms. No soybean variety is immune to the chlorosis, but large differences in yellowing and subsequent plant stunting occur between the most tolerant and most susceptible varieties. The most important management practice to reduce IDC is selecting chlorosis tolerant soybean varieties. At NDSU, scientists use a rating of 1 to 5 to score the IDC symptoms in plants, where 1 is green, 3 is yellow, and 5 is dead tissue.

A picture with soybean plants with different IDC scores and a listing of IDC ratings of varieties tested in 2019 can be found in the NDSU soybean variety trial results publication A843. If a field has IDC this year, it is critical to note which variety was used and what tolerance the variety has to IDC expression. It is vital to grow soybean tolerant varieties in fields more prone to IDC.

Other management strategies, in addition to variety selection, to reduce IDC include, proper field selection, a chelate Fe seed treatment with a proven track record of performance, an increase in seeding rate (Graph 2), seeding in wider rows with the same seeding rate (plants closer together within the row), managing the nitrate content in the field using a companion crop at the beginning of the season, and managing the crop to avoid additional stress conditions.

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Hans Kandel

Extension Agronomist Broadleaf Crops

 

Dave Franzen

Extension Soil Specialist

701-799-2565

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