Iron Chlorosis Shows Up On Soybeans

Cool early season temperatures have prompted soybean plants in a number of fields in certain Iowa areas to develop symptoms of iron chlorosis in 2002.

Soybeans plants that have iron chlorosis usually first show up in low and wet areas of soybean fields, says X.B. Yang, an Iowa State University extension plant pathologist. These fields often have a high soil pH (greater than pH 7) and poor drainage. Patches of soybean may turn yellow in low areas.

Symptoms of iron chlorosis are yellowing of the interveinal area of young leaves. Brown and necrotic spots may occur along the edges of the leaves. Plants can be stressed or killed if the disease is severe. Symptoms are more pronounced when soil temperature is low and soil moisture is high, he explains.

Root Fungus, SCN Are Often Involved

Often plants with iron chlorosis also suffer from root disease problems or soybean cyst nematode (SCN) infestation. If plants with iron chlorosis have root rot, their taproots have a dark brown or reddish brown discoloration, says Yang.

Several fungi can cause problems, with fusarium being the most common. Plants are weakened by iron chlorosis, which makes them more susceptible to invasion by fungal disease.

Iron chlorosis is a major disease in central and northern Iowa. In bean fields, there is plenty of iron in the soil. But iron becomes unavailable to soybean plants when soil pH is high, resulting in the iron deficiency in the plant.

High pH soils are favored by SCN, which may be a reason why cysts of SCN often are found on plants showing iron chlorosis symptoms, says Yang.

“If iron chlorosis is a problem in your fields, consider your management options for next years crop,” advises Yang.