Yellow soybeans

Farm Forum

This time of year it is not uncommon to see yellow soybean areas in the field. In the old days, yellow patches of soybeans were a sign that there were low areas high in pH that had iron chlorosis in the soybeans. This will stunt the crop, but it is usually only in small areas with poor drainage and higher salts so the pH is higher. Then there came Round-up ready soybeans and in some cases with overspray or double-ups there can be some yellow flash on the soybeans which will turn the upper leaves a bright yellow color. Usually in a short period of time the leaves green back up and the beans are fine. Then a few years back we started to see soybeans that were yellow on side hills in areas that were more eroded. It was found out that the areas were low in Potassium and the upper leaves showed the color. Then there are the people that look in the bottom of the soybean canopy and there are yellow leaves with brown spots. If there are enough brown spots the leaves may even be falling off. All soybeans will have this in wet years but it does not do enough damage to call for control measures.

Now there is another new way for soybeans to yellow that is just starting to happen in very limited locations and is usually limited to and is usually limited to low areas that have had soybeans in this area repeatedly over time. The areas that have yellow patches of soybeans are yellow in color and are stunted or the soybeans are very up and down looking. This problem comes from Soybean Cyst Nematodes. The nematode is only 1/32 of an inch long and white in color this time of year. You can find them on soybean roots and they are like white specs on the roots. Do not mix them up with nodules on soybeans that produce nitrogen. Nodules are a lot larger and more the color of the root. Soybean Cyst also can be checked for by taking a soil test in the fall and having the soil checked for Nematodes. This service has been free in the past and has been paid for by the South Dakota Soybean Council. If you are wondering about soybean cyst and if you might have them, then get Fact Sheet 902-A from your Regional Extension Center contact your Agronomy Field Specialist or me at 605-882-5140.