Why do my soybeans look like they are dying?

This week we have had numerous reports throughout Ohio, Indiana, Illinois and Kentucky regarding soybeans that are not looking as healthy as we like. The majority of soybeans have the outside of the cotyledons that look brown as well as the hypocotyl, especially when in the neck stage.This appears to be happening to all varieties from all companies, so it is not product specific.So what is going on?From what  I can tell there are two things happening.First, the vast majority of fields with this issue have been sprayed with a PPO inhibitor containing the active ingredient flumioxazin.These herbicides would include Valor®, Valor® XLT, Envive®,Enlight®, and Gangster®.
The herbicide label of Valor® actually states,“Crop injury may occur from applications made to poorly drained soils under cool, wet conditions.Risk of crop injury can be minimized by not using on poorly drained soils, planting at least 1.5 inches deep and completely covering seeds with soil prior to preemergence applications.” Several areas impacted received over 3” of rain which would constitute “poorly drained”in my opinion. There have been a few cases where other PPO inhibitors containing the active ingredient sulfentrazone (Authority® products and Sonic®) have shown the same symptoms.
For those fields that show damage I would suggest to check a few things.Open up the cotyledons to see if they are still green.Also check to see that the necks are still firm.If the necks are firm (even if they are brown) and the inside of the cotyledons are green then it is likely the plant will survive. You can also break open the neck to see if it is green as well.Look at the picture to the right that contains three plants. The plant to the left has wilted cotyledons and a shrunken, dried neck. The plant in the middle has green cotyledons, but the neck is not firm and the plant will die. The plant to the right has green cotyledons with a firm neck and will more than likely survive.Don’t think that PPO herbicides are bad – they are not. They have a risk as do all herbicides. PPO inhibitor herbicides have some great residual activity on many of our tough to control weeds such as marestail, waterhemp, and palmer amaranth.

The second picture shows a brown neck that is still firm with green cotyledons and will probably survive.
The second thing I have noticed is that there has been some damping off caused by Pythium.This should not be surprising since Pythium is a water mold and saturated soils are needed for infection.Large rainfalls within a week of planting is most favorable for damping off. The vast majority of fields with issues were planted between May 5-11 and the heavy rains were received last week – the perfect combination for Pythium infection.

What is an acceptable soybean population?

With reduced soybean stands the question becomes what is an acceptable population? The nice thing about soybeans is that they have the ability to make up for reduced stands. The chart below shows the potential yield by population. As you can see a population of 80,000 evenly spaced plants in 30” rows can still give approximately 100% of yield. Of course I know a reduced stand will not make it easy to sleep at night, but a soybean has many axillary buds that will create extra shoots which can make up for it. If it will make you sleep better at night you can fill in an existing stand, especially if a field has had
high yields in the past (>60 bu.).
To determine the population you will need to do a stand count.To determine the number of soybeans per acre on 30” rows, measure off 17 feet, 5 inches and count the number of plants.  This is 1/1000th of an acre so multiply the number of plants by 1000. For example, if you count 110 plants in 17’5”, multiply that by 1000 for a final stand of 110,000. Be sure to wait until all the plants have emerged.For drilled beans you can use a hula hoop to determine population.Figure out the diameter of the hula hoop.Throw the hula hoop and count the number of plants inside, then multiply the number of plants by the conversion factor in the chart below.
If you do decide to replant or are planting soybeans for the first time then be sure to increase plant populations. Depending on your current soybean seeding rate, you may need to increase plant populations the later we plant to increase the number of nodes.

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