Research Highlights

Finding the Best Management Strategy Combination in the Iron Deficiency Chlorosis Battle

By Carol Brown

Iron Deficiency Chlorosis (IDC) in soybeans can appear in soils with high pH that are common in western Minnesota and along the Red River Valley in North Dakota and Minnesota. It is an elusive soybean disease — appearing some years in some areas of a field, but in other years found in different locations or not seen at all.

University of Minnesota associate professor and Extension agronomist Seth Naeve is looking at ways to help farmers make the best economic and agronomic decisions to manage IDC in their soybean fields.

“The challenge is that Iron Deficiency Chlorosis is a messy problem,” says Naeve. “IDC has a lot of physical and chemical drivers; every square foot in a field seems to be different than the one next to it. But the soybean plant has a lot of physical mechanisms to deal with it. We’re trying to find the best combination of management that also keeps costs down for the farmer.”

Iron Deficiency Chlorosis is caused by low iron levels in the plant, resulting in yield loss in the affected field areas. Typically, the soybean plant will have one or two trifoliate leaves out before they start to turn yellow.

“The timing of IDC is predictable, we just don’t know how quickly soybeans will respond,” Naeve explains. “It seems different varieties have different trajectories. They may be yellow and stunted but they recover, whereas others take a long time to struggle through it. We are assuming — and studying — that the sooner we can get the plant green and the faster we reach canopy closure, the better.”

Through a two-year project supported by the Minnesota Soybean Research and Promotion Council, Naeve and graduate student Maykon da Silva are exploring management factors that farmers can use to combat IDC. The work is being conducted on private farms in the Red River Valley and outside the valley for data collection on different soil types. Within these farm fields, they have studies in areas with IDC “hot spots” and outside these hot spots in the same field.

“We hope to build models that can help drive prediction of IDC beyond these particular fields in our study,” Naeve says. “By measuring dates, plant stages and crop imagery via drone, hopefully we will be able to tell farmers that by a certain date or crop stage, they could see a certain percentage in yield loss. That is the ultimate goal.”

There are several strategies farmers can use for IDC management and Naeve is studying three main methods: using IDC-tolerant soybean varieties, higher plant populations, and an iron chelate additive. He is using a combination of these on the farms in the study.

He and his research team are looking to quantify answers to several questions, including:

• How much do IDC-tolerant soybean varieties gain in terms of response vs. cost?
• How much do higher seeding rates make a difference economically in reducing IDC?
• What rates of iron chelate application work best and make the most economical sense?

“We have these strategies in the fields in all combinations to see how they respond,” he says. “And a unique part of this trial is we are using nitrogen, not as a treatment per se, but to ratchet up IDC. We know that soil nitrates increase IDC, so we have plots with and without added nitrogen to ensure we can identify which treatments, or combinations, will give us the greatest response.”

In addition to finding good management combinations, Naeve and da Silva are looking at the strategies themselves. For the IDC-tolerant soybean varieties, they are measuring yield against seed cost. With the plant population aspect, Naeve says that closer plant-to-plant spacing within a row is important to help defend against IDC. Lastly, they are applying iron chelate in-furrow at rates of 0, 2 and 4 pounds. Additionally, they will measure the economic costs of all of these, alone and in combination, so the farmer can use these resources in the most economical way to fight IDC.

“IDC is a little unpredictable year over year and spatially within fields, so farmers can have difficulty deciding how to manage it,” he says. “Some of these tactics are relatively expensive and it may be hard to justify putting an extra $20 or $30 an acre into something they don’t know whether or not they need. It’s a challenging decision-making process.”

After the 2022 season, Naeve and da Silva will put pencil to paper with all the data collected over two crop years to find clear numbers of yield versus cost of the management strategies. These results will help them develop the model that could help farmers anywhere to combat IDC through the most economical means.

Published: May 2, 2022