Stressed Yellow Soybeans

By Mike Hannewald, Becks Field Agronomist

Yellow soybeans across northern Ohio can be attributed to multiple compounding stress factors according to Mike Hannewald, Field Agronomist for Becks. “If you see yellowing in your soybean field, there could be several different causes.”

It can be helpful to select a healthy soybean plant to use as a comparison when determining stress issues in other unhealthy beans. “A healthy bean plant will have healthy roots with several nodules. If you break open a nodule, it should be a rusty red color and that tells you that it is producing nitrogen,” said Hannewald. “That is what we want to see this time of year.”

One of the first stress factors to consider when evaluating a yellow soybean field is herbicide injury. “While you might just be spraying Round-up® or Liberty ® or Enlist ®, and the soybeans have that trait package, the bean plant still needs to metabolize that herbicide. Due to the other compounding stresses in the field, that metabolization is not occurring without showing stress in the plant,” said Hannewald. “Often this may be observed in the end rows where spray overlapping occurred and brown spots or discoloration is evident on the leaves.”

A nutrient deficiency may also be a stress factor. If there are discolored areas in a field and it does not have the characteristics of herbicide injury, or if the field was not sprayed, then Manganese deficiency could be the culprit. “Manganese deficiency occurs almost every year in Ohio and can be observed anytime you have less than ideal conditions and the roots struggle to take up Manganese,” said Hannewald. “You will start to see the yellowing and interveinal chlorosis, which is yellow in-between the veins, and the veins stay green, but the discoloration stays yellow and does not further deteriorate, that is likely Manganese deficiency and can be treated with a simple foliar fertilizer application containing Manganese.”

“If that yellowing of the leaves progresses further and the leaf turns brown and wilts, that may be a disease rather than a deficiency,” said Hannewald. “We have been observing fusarium wilt, which is a disease that we don’t usually deal with in Ohio. It requires some unique conditions to occur. The disease causes the roots to effectively shut down and the leaves will look like sudden death syndrome and eventually fall off. This often occurs in individual plants or small areas, usually in the wetter parts of the field.”

Fusarium wilt at first glance can look like phytophthora,” said Hannewald. “With Fusarium wilt the leaves will turn brown and fall off. With phytophthora the leaves turn brown but will stay attached to the plant longer. If you look at the stem it will be green or purple all the way down for Fusarium wilt. If you split the stem open and look at the pith it will be brown. With Phytophthora the stem will turn brown on the outside, and when you break the stem open the pith it will be green or white.”

Weather conditions are also a factor in plant stress and compounding with other issues. “We have had drought conditions for more than three weeks in some places with no rain followed by saturated wet conditions,” said Hannewald. “It may come as a surprise because those rains seemed to be a lifesaver to help the plants take off and grow, but they also allowed the diseases to take off.”

“When it comes to root and stem rot, there is not a great course of action,” said Hannewald. “A fungicide is not going to bring the soybeans back to life. Some plants may recover on their own, and some may die. One recommendation is that if a herbicide application is planned to be made already, then adding a foliar feed with it may be beneficial to reduce stress. Adding Manganese and Sulfur and perhaps Fulvic Acid are things that have shown consistent results in the Becks PFR Proven tests and those nutrients are also known to help reduce stress in plants. In the long run, favorable weather, timely rains, and oxygen to the roots will help most of the plants recover.”

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