Tips for soybean scouting after rain

July 9, 2026 | Kriss Nelson

Heavy rainfall across parts of Iowa last week left ponded soybean fields and plenty of questions about what comes next. Iowa Soybean Association Research Agronomist Avreeanna Tweedy shares what farmers should scout for first as fields begin to dry and recover.

Q: Where should farmers start scouting after heavy rainfall?

The biggest thing is waiting for the water to go down and then assessing how long those soybeans were underwater and whether they were completely submerged or still had some of the canopy above water. Areas that were underwater for several days are obviously going to be at a greater risk for injury and stand loss.

I wouldn’t make management decisions right away. Give those plants a few days and then go back and look for new growth and improving plant color. Dig some plants and look at the roots to see if they’re healthy or starting to discolor or rot. 

There isn't an exact number of days a soybean plant can survive underwater because it depends on crop stage, temperature, water movement and whether the canopy remained above water. Warm, stagnant water is generally more damaging, and the risk of injury and plant death increases the longer soybeans remain completely underwater. Plants that had some of the canopy above the water generally have a better chance of recovering.

By the second week of July, replanting generally isn’t a practical option for most soybean fields in Iowa because of the limited remaining growing season, declining yield potential with delayed planting, and the added cost of establishing a new crop. At this point, the focus is determining how much of the existing stand remains viable, whether plants are recovering and what secondary problems may develop.

Another thing I’d keep an eye on as the water goes down is weed control in those ponded areas. Flooding and crop injury can thin the stand or delay canopy closure, which gives weeds more opportunity to establish. Farmers should revisit those areas, identify emerging weeds and consider what control options remain based on weed size, crop stage and herbicide label restrictions.

Q: What does saturated soil do to soybean roots and nodules?

When soils remain saturated, oxygen becomes limited around the roots, temporarily slowing root activity and nitrogen fixation. If saturated conditions persist, roots and nodules can begin to deteriorate.

Once the water goes down, I’d dig some plants from the affected areas and check the roots and nodules. Splitting nodules open is a simple way to check whether they’re actively fixing nitrogen; they should be pink or reddish inside.

Yellow plants after flooding don’t automatically mean the nutrients are gone from the soil. The roots may be stressed or damaged and simply unable to take up nutrients efficiently until the soil drains and the plant starts recovering.

Q: What diseases deserve the closest attention after flooding?

Over the next couple of weeks, I’d be watching flooded areas closely for plants that continue to yellow, wilt or die even after the rest of the field starts recovering. Phytophthora root and stem rot and other root rots are some of the bigger concerns after prolonged saturated conditions. Digging plants and examining the roots and lower stems can help distinguish flood injury from disease.

Sudden death syndrome is also something I’d keep on the radar as we move further into the season. Infection typically occurs earlier, but foliar symptoms can show up later as soybeans move through reproductive stages. Farmers should watch for yellowing and browning between the leaf veins while the veins stay green.

Bacterial blight may also become more noticeable after heavy rainfall, wind or hail because storms can spread bacteria and create wounds that allow infection. It’s important to remember that bacterial diseases aren’t controlled by fungicides.

As far as insects, I wouldn’t assume that heavy rainfall means insect pressure will automatically increase or disappear. I’d continue scouting for insect activity and defoliation, especially in areas with delayed crop development, reduced canopy closure, or increased weed growth.

Q: When does a fungicide application make sense?

I wouldn’t recommend a fungicide application based solely on wet weather or symptoms appearing in the field.

Correctly identifying the problem comes first. Fungicides won’t control bacterial diseases, reverse flooding injury, or repair damaged roots. I think a fungicide discussion makes more sense when we know the disease present can actually be controlled by a foliar fungicide and the crop stage, field history, disease pressure, and weather conditions support an application. Otherwise, continued scouting and monitoring symptom development is often the better approach.

Written by Kriss Nelson.

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