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E. Indiana and Ohio: Yellow Beans, Rapid Growth Syndrome, and Floppy Corn

06/26/2014 @ 8:48am

Yellow Beans

While driving through Indiana and Ohio there are many soybean fields that are pale yellow in color as the picture below shows. We have had adequate moisture and above-average temperatures, so what is going on? In most cases the soybeans are lacking nitrogen. Soybean plants receive the vast majority of their nitrogen by bacteria fixing atmospheric nitrogen. Here are a few facts about soybeans, nitrogen needs, and nodulation:


  • Soybeans need about 5 pounds of nitrogen per bushel. This means for a 60 bu./A. yield that soybeans need about 300 pounds of nitrogen - those bacteria have a lot of work to do.

  • The bacteria to fix nitrogen are located on the roots, so air needs to be exchanged in the soils. Tight or compacted soils with less air exchange will produce fewer nodules. In addition to fixing nitrogen, bacteria also need oxygen to live.

  • The bacteria, Bradyrhizobia japonicum, will begin to invade the root usually within a week after emergence. Once it infects the root, it takes a few more weeks for the bacteria to multiply to levels to start feeding the plants. During this time, your plants may be yellow. The picture on the left shows young, immature nodules forming on a plant that is in the unifoliate stage. The plant on the right is at V3 and has more mature nodules that are producing nitrogen. The leaves are not yellow.


  • Nodules (which are made of bacteria) will reach maximum size about 28 to 37 days after the initial infection and will usually keep producing nitrogen for about 60 days.

Nodules and soybeans have a symbiotic relationship. The bacteria are fed sugars from the photosynthates made from the plant while the bacteria provide nitrogen. The bacteria do take energy away from the plant. If there is residual nitrogen in the soil, then the plant will take up this form because it is easier rather than waste energy to feed nodules.

When the nodules are forming and there is not a lot of residual nitrogen in the ground, then the soybean plants will look a pale yellow like they do in many fields now. This is actually a good thing that we are forcing nodulation. Wait a week or two, and the soybeans should be turning a dark green.

Rapid Growth Syndrome

Recently, there have been a few reports of corn that looks like it is getting wrapped up in itself like the picture on the left below. This is known as rapid growth syndrome or some call it twisted whorl syndrome.

This syndrome happens somewhere every year. It most often occurs on corn that is in the V5 to V7 stages of growth. It usually happens when we have good growing conditions followed by a short burst of colder temperatures (and often a rainfall that accompanies it) followed by warm temperatures again. This is exactly what happened last week; highs were in the upper 80s on Tuesday, followed by a cold and rainy Wednesday with highs only in the low 70s, and then it warmed up to the 80s again on Friday. Some genetics will show this more than others.

The good news is that corn will grow out of this (as the corn picture on the right has already done) with no yield loss. In fact, in a few days it will hardly be noticeable except for a few crinkled leaves.


Floppy Corn

There have been a few reports of corn that is leaning over after storms from last Wednesday. Genetics do not seem to play a role as many companies and hybrids have shown this symptom. All the corn is laying the same direction, which certainly means that wind played a role, however, it was not overly windy last Wednesday. There are a few things that could be causing this such as growth-regulator herbicides, shallow planting depths, underdeveloped nodal root systems (especially from plantings around Mother’s Day weekend), and so on. The good news is that most corn has grown out of this or should grow out of it shortly.


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