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How to Manage Soybean Iron Deficiency Chlorosis

Tolerant varieties are the best way.

If North Dakota and Minnesota ever decided to become a separate country, the combined states could be called Chlorosis Country.

That’s because this area is especially prone to iron deficiency chlorosis (IDC) in soybeans. After an initial dry start to the soybean growing season, rainfall in the last week or two has provided conditions for iron deficiency chlorosis (IDC) to show up in the region, says Hans Kandel, North Dakota State University (NDSU) Extension agronomist.

Symptoms

Soybeans suffering from IDC exhibit the usual suspect symptoms of chlorotic leaves and stunted plants. Severe IDC cases may turn leaf tissue brown and cause necrosis, says Kandel. Plants with chlorosis are often stunted and behind in growth and development compared with healthy plants. Soybean plants may grow out of the chlorosis and become green again. However, IDC may reduce yields. 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 frustrating factor for managing iron chlorosis is that there’s no one factor that causes it. A combination of factors like soil pH and calcium carbonate salts contribute to the malady, says Alan Scott, a technical product manager for Corteva Agriscience, Agriculture Division of DowDuPont.

“Even in a field, areas will vary (for iron chlorosis),” says Scott. “That is what it makes it tough to characterize.” IDC often occurs on calcareous soils, which are often referred to as alkaline and are characterized by their high pH values (greater than 7.5 on the 0 to 14 pH scale). 

However, chlorosis of soybeans does not occur on all high-pH soils, note Corteva Agriscience scientists. Soil tests of the surface soil in chlorotic and nonchlorotic areas of a field often are similar. However, differences may pop up in the subsoil.

Enter Tolerant Varieties

Soybean varieties that tolerate iron chlorosis are the best way to deal with the malady. Pioneer varieties from Corteva Agriscience are rated for iron chlorosis tolerance on a 1 to 9 scale. The higher a variety ranks on the scale, the more it tolerates iron chlorosis.

In North Dakota, a listing of IDC ratings of varieties tested in 2017 can be found in the NDSU soybean variety trial results publication.  The IDC scores for varieties tested in 2018 will be available this fall. If a field has IDC this year, it is critical to note which variety is used and what tolerance the variety has to IDC expression. It is vital to grow soybean-tolerant varieties in fields more prone to IDC, says Kandel.

Molecular marker technology has helped develop varieties that tolerate iron chlorosis with no yield drag. Molecular markers are DNA regions that can be associated with different genes and traits, note Corteva Agriscience officials. Scientists rapidly screen for markers to pick traits faster than possible with traditional breeding and speed product development.  

“It also gives us the ability to cut through the misconception that some varieties with iron chlorosis tolerance had a bit of yield drag,” adds Scott. Yield drag doesn’t exist with these varieties, he notes.

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