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Mystery of the rotting soybean cotyledons

Mystery of the rotting soybean cotyledons
Why are soybean seedlings dying as they emerge in this field?

A farmer called us out to look at fields where some of his soybeans were dying soon after they emerged. Specifically, they appeared to be rotting and breaking in the crook of the neck just below the cotyledons. It appeared to be happening either as or soon after the seedlings attempted to emerge.

Related: Why herbicide labels don't always agree with one another

Agronomists say we asked the right questions. We just didn't get answers that added up to a clear cause-and-effect solution.

Were all the fields planted the same day? No.

Were all the fields planted to the same variety? No, there were two varieties, and both were affected.

Were there fields where these varieties weren't affected? Yes.

Find a cause: What caused these soybeans to rot and die and neighboring plants remain healthy is still unclear. If you have thoughts about the cause, email [email protected]

Was it no-till or conventional till? It was no-till, but some ends were ripped and resembled conventional tillage. The problem was just as noticeable there.

Do you plant all these fields in order, without planting other fields in between? No. Fields planted in between planting these four were not affected.

What was the herbicide burndown? Authority at 3.2 ounces per acre and Sharpen, the same mix we have used without injury for several years. "In fact, we used a lower rate of Authority this year than in the past."

Did you spray before or after planting? We sprayed about three to five days before, depending upon the field. (That's an important question – Bill Johnson, Purdue University Extension weed control specialist, says sometimes when the herbicide is sprayed afterwards, and a big rain occurs, herbicide can splash onto emerging cotyledons and cause injury. That wasn't the case here.)

Does there seem to be a soil type connection? No, soils ranged from moderately sandy to a medium loam to moderately fine on eroded hills. There were similar patterns of damage in all types of soil.

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What was the previous crop grown in these fields? Popcorn was grown in three of them, but conventional corn was grown in the fourth one. All four had the same type and amount of damage.

Are there other questions to ask? Probably. Samples were sent to the Purdue Plant Diagnostic Lab. We'll share those results when we get them. The seed dealer and chemical rep are leaning toward chemical damage, but the jury is still out on this one.

TAGS: Extension
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