In 1976, kochia became the first weed to show herbicide resistance in the Corn Belt.¹ Fast forward 20 years, and not only have herbicide-resistant plants spread throughout the U.S., the challenge of complete herbicide effectiveness grows each season. In the U.S., there were 81 weed species showing herbicide resistance in 2019, up from 51 in 2000. To stay ahead of the curve, we must acknowledge weed challenges on the horizon and adapt our weed resistance management practices accordingly.

First, a brief primer on the 2 types of herbicide resistance: target site and metabolic. Target site is the most common form of herbicide resistance found in the U.S., and occurs when the herbicide reaches its targeted site of activity but is unable to act. This will happen when the same sites of action are repeatedly applied. Metabolic resistance happens when the weed is able to metabolize or break the herbicide down into a form that will not kill the weed.

While researchers suspect it takes longer for metabolic resistance to develop and spread compared to target site resistance, it’s an alarming development, as an alteration in resistance to one herbicide group may provide cross-resistance to several classes of herbicides – even those that the weed has never come into direct contact with.

To help delay the development of both target site and metabolic resistance, follow these 4 strategies:

1. Apply a preemergence herbicide with multiple effective sites of action.
2. Use several sites of action for control to increase the likelihood that a weed will be killed, instead of recovering and spreading resistant genes.
3. Use full label herbicide rates and apply at the proper timing, using overlapping residuals to provide full-season control.
4. Practice diversity by incorporating cultural practices such as scouting, narrow row spacing and cleaning farm equipment between fields and harvests.

There are a number of quality, proven herbicides available to help growers manage and delay weed resistance. For soybeans, we recommend a preemergence application of Boundary^® 6.5 EC, BroadAxe^® XC or Prefix^® herbicides followed by Tavium^® Plus VaporGrip^® Technology herbicide. These combinations will provide 3 effective sites of action.

For corn, we recommend Acuron^® herbicide, which can be followed by Halex^® GT corn herbicide with either atrazine or dicamba. This program provides numerous effective sites of action, and as an added bonus, Acuron delivers 5 – 15 more bushels an acre by controlling the tough weeds other herbicides miss.²

Weed resistance is a real and growing threat to corn and soybean growers, but by using a strong herbicide program with multiple sites of action, you can fight back.

See how weed resistance has spread across the U.S. in the last 50 years, and learn more about how to keep tough weeds from jeopardizing your profits.

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¹ Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet. Monday, November 4, 2019. Available at http://www.weedscience.com.

² When applied preemergence and at full label rates. Acuron yield advantage range based on 2016 Syngenta and University trials comparing Acuron to Corvus®, Resicore®, SureStart® II and Verdict®. For more information on Acuron versus an individual product, ask your Syngenta representative.