If your soybeans turn yellow this spring with iron deficiency chlorosis (IDC) and then green back up, how much yield did you lose?

“My research, going back almost 20 years, shows that there is a very strong relationship between the severity of chlorosis at the 5-6 trifoliate stage and final yield,” says Dave Franzen, North Dakota State University Extension soils specialist.

In NDSU research done in 1998-2000, nine to 19 bushels per acre were lost per unit of chlorosis at the 5-6 leaf stage, depending on the year. A unit of chlorosis refers to the rating scale that NDSU specialists use describe the severity of chlorosis.

A rating of 1 means that the plants are normal and dark green.

A rating of 2 means that the upper leaves have yellowed a little, but the veins and tissues are the same color. The chlorosis does not have an "interveinal" nature.

A rating of 3 means that the upper leaves have interveinal chlorosis. The veins are green and the tissues between the veins are yellow.

A rating of 4 means that the upper leaves have interveinal chlorosis, and necrosis (dead spots) is setting in, but the growing point does not appear to be damaged.

A rating of 5 means that there is interveinal chlorosis on the upper leaves, necrosis is setting in and the growing point is visibly damaged.

Additional studies conducted in 2009 using three varieties and two rates of iron fertilizer gave an estimate of about 13 bushels per acre lost per unit of chlorosis.

“So, if there is a small degree of chlorosis early, and the crop fully recovers before the 5-6 trifoliate stage, there probably isn't much yield loss,” Franzen says. However, chlorosis that persists to the 5-6 trifoliate stage definitely reduces yield, even if there is recovery later.”

Controlling iron deficiency chlorosis

The most effective chlorosis control measure is to plant an IDC-resistant variety, Franzen says.

“If variety selection is not enough to eliminate chlorosis, then a resistant variety should be planted with 2-3 pounds per acre of a high-quality FeEDDHA product [iron chelated with ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid)] applied in-furrow at planting,” he says. “The quality of FeEDDHA fertilizer varies from manufacturer to manufacturer, however. The best FeEDDHA products in the marketplace have about 80% of the iron in the most effective form, the ortho-ortho isomer.”

Fertilizing a chlorosis-susceptible variety with FeEDDHA may improve the yield of the susceptible variety, but the yield will still be less than if a resistant variety had been planted, Franzen says.

Source: NDSU, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.