ILSOYADVISOR POST

Management guidelines for soybeans under stress

In many parts of the state we have been plagued by saturated soils from a very early time. We continued to get record rainfall from April, when most farmers would think about planting, all the way through today. This has caused not only late-planted soybeans, but soybeans that in a lot of cases were planted into less than ideal soil conditions and are experiencing continued saturated soil conditions. This has caused soybeans to take a long time to emerge and they seem to have struggled to grow ever since. Recent warm weather has helped pushed beans along a little, but with saturated soils we’re still seeing soybeans with slow growth.

The most common symptoms observed have been slow emergence, reduced early vigor, yellowing of lower leaves, necrosis or death, poor root systems and lack of nodule formation. The main cause for these symptoms can be attributed to saturated soils, which has caused a lack of oxygen and poor root development. We then saw problems like nutrient deficiencies and lack of nodulation. Determining how to overcome these problems may require practices and products that we don’t typically use. 

Nitrogen: When we see yellow and stunted crops our minds automatically think nitrogen (N), and rightfully so. Applying nitrogen to soybeans is still a somewhat controversial topic. We know that soybeans will begin fixing their own nitrogen and rarely recommend adding N to this crop. There is concern that giving the soybean N early on will make it lazy and not able to produce the nitrogen it needs later in the season. However, I think we are seeing a lack of nitrogen availability in small soybeans that are not yet fixing N and seeing issues with larger soybeans being able to fix their own nitrogen. I think the addition of a small amount of N may give the soybean just the boost it needs. Be cautious on applying too much, though.

Key nutrients: A few other key nutrients of interest are sulfur (S) and molybdenum (Mo). More soybeans are receiving planned applications of sulfur than ever before. With less sulfur available through acid rain we are seeing a larger need for sulfur applications. Sulfur helps promote nodulation in soybeans, is required for chlorophyll production and aids in seed production. Sulfur is mobile in the soil, so it may have been leached out with all the rain. Molybdenum is vital for fixing nitrogen by rhizobia bacteria. It can also move through the soil profile and may have leached out. The addition of S and Mo are likely to help soybeans that are struggling to produce nodules and begin fixing N.

Foliar feeding: Another idea would be an application of foliar fertilizers in the POST herbicide trip. Before making a fertilizer application it’s important to identify which nutrients are lacking in the plant. A tissue sample, along with a soil sample, will help determine the best route to take. I believe that we may not be lacking nutrients in the soil, but because of poor root development we are seeing nutrient deficiencies in the plant. Giving the soybeans the needed nutrients through either a foliar fertilizer with herbicides or a topdress application could be extremely beneficial this year. Make sure the product you use has a high concentration of the needed nutrients because those with only small concentrations won’t last long if conditions don’t improve. 

Aeration: One highly unpopular recommendation would be to cultivate if you are able. This would help to dry and put oxygen back in the soil. However, I realize that most growers probably don’t own a rotary hoe or row crop cultivator in an era of reduced and no-till, with herbicides to control weeds.

Disease risk: Disease management will play an important role in protecting the soybean crop we have. If we continue to receive wet weather, we will likely see foliar diseases like white mold and frogeye leaf spot develop. Scout fields and be prepared to make foliar fungicide applications at R3 to protect soybeans from these pathogens. Sudden death syndrome (SDS) is going to be something to watch for if we continue to have wet conditions during flowering, followed by warm, dry conditions after flowering. This disease infects the soybean during early growth but is not recognized until later in the season. It is more prominent in years where we have cool, wet weather at planting, which we had this year. Unfortunately, the only way to control this disease is with seed applied fungicide treatments like ILeVO®. 

We’ve still got a long way to go to start predicting yields. Favorable conditions from here on out are going to be necessary to see average or above average yields. Although I don’t anticipate many record-setting soybean fields this year because of the late planting and slow growth, I haven’t completely written off our ability to maintain good yields. 


Tracy Heuerman

Heuerman has worked within the Growmark system for nine years, as both a crop specialist and in her current role as a Field Sales Agronomist. She enjoys helping growers achieve maximum ROI by implementing strategies to increase yields. Raised on a family farm in south central Illinois, Tracy is still involved in growing corn, soybeans and wheat with her family. She holds a bachelor’s in agriculture economics and a master’s in plant and soil science, both from Southern Illinois University - Carbondale. She can be reached at theuerman@growmark.com.



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