Published on Thursday, July 4, 2019
With the new herbicide-tolerant traits on the market today and the many to come in the near future, this is a good opportunity to discuss some common herbicide injury symptomology that is documented every year.
To begin, it's important to note that auxin-based herbicides are prone to off-target movement through physical drift, tank contamination, or secondary movement (i.e. volatility and temperature inversions). Because of this, auxin-based symptomology is becoming more common, specifically from 2,4- D and dicamba. Even though these two herbicides have the same mode of action, they have different chemical families. Dicamba is a benzoic acid and 2,4-D is a phenoxy. Because they come from different families, 2,4-D and dicamba cause different symptoms to soybeans exposed to low levels. A few of the distinguishing characteristics of 2,4-D are stem twisting, leaf drop, leaf strapping, and calleous tissue formation on the stem. Dicamba exposure to non-tolerant soybeans will express as leaf cupping, shortened internode and height reduction, and, sometimes, death of the apical growing point.
Purdue Extension developed an excellent publication that helps differentiate 2,4-D vs. dicamba injury on soybeans. You can view it by clicking here.
Group 15 and 14
Another group of herbicides that we often see damage from on soybeans are the Group 15 or long chain fatty acid inhibitors. This herbicide group includes Dual®, Outlook®, Warrant® and Zidua®. These products are used for their residual benefits and are often paired with another herbicide that offers post-emergence activity. Typically, injury symptoms from this class include crinkled/cupped leaves and shortened leaf mid-ribs. The shortening of leaf mid-ribs will result in blunt or heart-shaped leaf tips. Damage is more likely when there are cool, wet conditions at emergence.
Finally, damage from Group 14 or PPO inhibitors is commonly seen on soybeans. In this group of herbicides, some products can only be applied pre-emergence on soybeans and some can be applied either as a pre-emergence or post-emergence application. Some of the pre-emergence only herbicides include Valor®, Sharpen®, and Authority® based products. Damage from these herbicides will typically be expressed as burn on the hypocotyl or cotyledons. Some of the PPOs that can also be sprayed after the soybeans have emerged include Flexstar®, Cobra,® and Ultra-Blazer®. These herbicides will typically burn the soybean foliage, leaving a bronze appearance to the field for several days.
There are many other herbicides that can cause injury to soybeans that may look similar to some of the pictures shown in this article. Please reach out to your local Beck’s representative to better identify herbicide injury in your fields.
Sharpen® and Zidua® are registered trademarks of BASF. Warrant® is a registered trademark of Monsanto Technology, LLC. Sonic® and FirstRate® are registered trademarks of The Dow Chemical Company (“Dow”) or an
affiliated company of Dow. Dual II Magnum® and Flexstar® are registered trademarks of a Syngenta Group Company. Authority® is a registered trademark of FMC Corporation. Valor® and Cobra® are registered trademarks
of Valent U.S.A. LLC. for optimum yield and excellent weed control. Authority® is a registered trademark of FMC Corporation. Ultra-Blazer® is a registered trademark of United Phosphorus, Inc.
Author: Austin Scott
Categories: CropTalk, 2019
Tags: CropTalk, soybeans, herbicides, Dicamba, 2019, auxins, 2, 4-D