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Soybean herbicide injury due to perfect storm

Soybean herbicide injury due to perfect storm
Combination of factors led to isolated soybean crop herbicide injury this year.

The farmer who contacted us wondered why his soybean stand was 100,000 or fewer in 15-inch rows. He noticed cotyledons rotting and dropping off on some soybeans soon after they emerged from the ground.

Related: Mystery of the rotting soybean cotyledons

Everyone he has talked to said it points toward herbicide injury. He sprayed the field before planting with Sharpen plus Authority. It's the same combination he has used successfully in seasons before this one, and it didn't affect all fields this year.

Struggle! Some soybean seedlings planted deep and growing slowly in cool soil took in more herbicide near the surface than they could handle in some fields.

Sarah Hanson, Johnson County Extension ag educator, obtained samples of affected seedlings. She elected to contact Shaun Casteel, a Purdue University Extension soybean specialist. She also described the seedlings to him. Her other option would have been to submit the samples directly to the Purdue University Plant and Diagnostic Clinic. They route the samples to the right expert. There is a charge for using their service.

Hanson reports that Conley, like most other advisers and agronomists who have viewed the field, believe insecticide injury was involved. However, like Bill Johnson, Purdue University Extension weed control specialist says, the only cause is hardly ever, if ever, herbicide injury alone.

According to Hanson, Casteel surmises that the seeds were planted a bit deeper than normal. That's judging from the length of the hypocotyl, or stem bringing the cotyledons above ground. Each cotyledon was originally half of the soybean seed.

Temperatures turned cool and it was wet, although not saturated, for several days after planting. He surmises that sitting in the soil, as the cotyledons finally reached toward the surface, they encountered the herbicide. Not growing quickly, they absorbed it and were affected, rather than popping through the soil quickly before absorbing enough herbicide to cause damage.

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

Not all seeds were affected. In fact there was enough stand remaining that the farmer chose not to replant. He also says he will likely continue using Authority in the future. His conclusion is that several things went against these fields, and it may not happen again.

TAGS: Extension
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