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Integrated Crop Management News Extension and Experiment Station Publications

5-25-2017

Evaluating Herbicide Injury on Soybean

Robert G. Hartzler

Iowa State University, hartzler@iastate.edu

Follow this and additional works at:https://lib.dr.iastate.edu/cropnews

Part of theAgricultural Science Commons, and theAgriculture Commons

The Iowa State University Digital Repository provides access to Integrated Crop Management News for historical purposes only. Users are hereby notified that the content may be

inaccurate, out of date, incomplete and/or may not meet the needs and requirements of the user. Users should make their own assessment of the information and whether it is suitable for their intended purpose. For current information on integrated crop management from Iowa State University Extension and Outreach, please visithttps://crops.extension.iastate.edu/.

Recommended Citation

Hartzler, Robert G., "Evaluating Herbicide Injury on Soybean" (2017). Integrated Crop Management News. 2423.

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Evaluating Herbicide Injury on Soybean

Abstract

The potential for herbicide injury with preemergence herbicides is greater with soybean than corn. The risk increases with environmental conditions that reduce crop vigor and growth rate, and also with heavy rain that moves the herbicide to the depth of the germinating seed or emerging seedling. Much of the state has

experienced these conditions, thus it is likely symptoms will be found in many fields as people return to the field with the improved weather.

Disciplines

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Integrated Crop Management

Evaluating Herbicide Injury on Soybean

May 25, 2017

The potential for herbicide injury with preemergence herbicides is greater with soybean than corn. The risk increases with environmental conditions that reduce crop vigor and growth rate, and also with heavy rain that moves the herbicide to the depth of the

germinating seed or emerging seedling. Much of the state has experienced these

conditions, thus it is likely symptoms will be found in many fields as people return to the field with the improved weather.

Sulfentrazone (Authority mixes) and flumioxazin (Valor) are Herbicide Group (HG) 14 (PPO inhibitors) products with a relatively high risk of injury. Injury is most likely when rain increases herbicide availability as the hypocotyl approaches or emerges through the soil surface. Symptoms include necrotic lesions on the cotyledons and hypocotyl, and often are more severe in poorly drained areas of the field (Figure 1). In worse case

scenarios, the hypocotyl can be girdled, resulting in plant death (Figure 2). The herbicide may contact the apical bud, this results in malformed leaves and occasionally death of the primary stem. Since HG 14 herbicides are contact materials, soybean usually recover quickly from the injury, except in cases where the hypocotyl is girdled or apical bud is damaged. The low use rate of saflufenacil (Sharpen) in soybean reduces, but

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Figure 4. Damage to growing point from combination of flumioxazin, pyroxasulfone, and heavy rain at emergence.

Metribuzin (HG 5) causes interveinal chlorosis and necrosis on emerged leaves (Figure 5). Symptoms typically appear on unifoliates and the first trifoliate leaves, later-emerging leaves are usually unaffected. In worst-case scenarios, two or three nodes of leaves may be killed. The risk increases in fields with high pH soils due to greater availability of the herbicide.

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Figure 5. Interveinal chlorosis/necrosis caused by metribuzin. Image provided by

Aaron Hager, U of Ill.

Pendimethalin and trifluralin (HG 3) cause swelling of the hypocotyl, reduced root growth, and delayed emergence (Figure 6). Injury is most likely where cool, wet soils slow

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Figure 6. Swollen hypocotyls associated with HG 3 products and cool, wet weather. Image

provided by Aaron Hager, U of Ill.

Crop injury is a risk associated with using herbicides, the lower herbicide tolerance of soybean than corn increases the likelihood of damage. Most preemergence products used in soybean are either contact or xylem mobile herbicides, thus little herbicide reaches the growing point under most situations. This increases the likelihood that injured crops will quickly recover from the damage, minimizing the risk of yield loss. Where injury is

evident, stand counts should be taken to determine if stand loss has occurred, fields should be closely monitored over the next few weeks to document recovery, and finally, any field operations that could place additional stress on the crop should be avoided until normal growth resumes.

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article is to be used in any other manner, permission from the author is required. This article was originally published on May 25, 2017. The information contained within may not be the most current and accurate depending on when it is accessed.

Category: Weeds

Crop:

Soybean

Tags: herbicide injury crop response

Author:

Bob Hartzler Professor of Agronomy

Dr. Bob Hartzler is a professor of agronomy and an extension weed specialist. He conducts research on weed biology and how it impacts the efficacy of weed management programs in corn and soybean. Dr. Hartzler also teaches undergraduate classes in weed science and weed identificatio...

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