Herbicide Resistance in 2026: A Plan for Corn, Soybeans & Cereals

Weed control in 2025 wasn’t simple and 2026 isn’t likely to be any less complex. The number of herbicide resistant weeds continues to increase — up 175% since 2000¹. Growers must consider if they’re dealing with target-site or non-target-site resistant weeds. Smart and effective control means being selective with which herbicides you apply, as well as when and how you apply them. Successful resistance management requires knowing your weeds, knowing your options and making a plan.

Target-site vs. Non-target-site Resistance

The target-site within a weed refers to the specific site where the herbicide binds with the weed, thereby blocking or inhibiting a necessary physiological process of the plant and causing injury or death. Target-site resistance is the familiar herbicide resistance challenge that growers have heard about for years. Resistance is caused by a mutation in the weed’s target-site, ultimately disrupting an herbicide’s ability to bind with the target site within the weed and rendering the herbicide ineffective.

Target-site resistance is largely predictable because if a weed shows resistance to one herbicide within an Herbicide Resistance Action Committee (HRAC) group, then the other herbicides within that group are also likely ineffective. This is why it’s important to rotate modes of action in your herbicide program.

Non-target-site resistance, one category of which is metabolic resistance, is far less predictable than target-site resistance and is increasingly problematic. Non-target-site resistance results when weeds develop the ability to subvert herbicides by metabolizing, storing or detoxifying them so that they never reach the target site. It extends beyond any particular herbicide group and can impact multiple modes of action. In this case, rotating to a new mode of action may not help.

Worst of the Worst Weeds in 2025

So, what were the worst weeds of 2025 and why? Three technical product leads from Syngenta, managing products in soybeans, corn and cereals — Eric Palmer, Ph.D., Mark Kitt and David Belles, Ph.D. — contributed their insights to the following list.

Palmer amaranth (Amaranthus palmeri) – Amaranthaceae family

• Can produce more than 400,000 seeds in a season when left unchecked
• Can contribute to yield losses of up to 91% in corn and 79% in soybeans
• Exhibits non-target site resistance and resistance at multiple sites of action.

Waterhemp (Amaranthus tuberculatus) – Amaranthaceae family

• Can produce up to 1,000,000 seeds in a season when left unchecked
• Exhibits non-target site resistance and resistance at multiple sites of action

Wild Oat (Avena fatua) – Poaceae family

• Reproduces from seed and emerges in cool and wet soils
• Produces an average of 60 seeds per plant
• Reduces crop yields and increases production costs

Kochia (Kochia scoparia) – Amaranthaceae family

• The number of seeds produced by individual plants varies widely, but can reach up to 30,000
• Exhibits resistance at multiple sites of action

Marestail (Conyza canadensis) – Asteraceae family

• Can produce 200,000 highly mobile seeds per plant
• Was the first glyphosate-resistant weed identified in U.S. row crops in 2000 and today shows resistance at multiple sites of action.

Giant ragweed (Ambrosia trifida) – Asteraceae family

• Can produce up to 5,000 seeds per plant
• Season-long competition can lead to crop losses of 30 – 90%
• Exhibits resistance at multiple sites of action.

Decisions for a Successful 2026 Season

With the threat of metabolic resistance present, Eric Palmer, Ph.D., soybeans technical product lead at Syngenta, uses the metaphor of a slide dimmer light switch to explain the importance of using preemergence herbicides. “Just as the light level in a room starts low and builds as you move the switch up, the concentration of the enzymes in a weed that break down and metabolize herbicide chemistries build up as the weed grows,” he says. “This is why programs incorporating preemergence residual herbicides are more successful than those with postemergence applications alone.”

There is a lot of testing done to determine the proper rate of application on the herbicide label. This testing encompasses both crop safety and how much herbicide is required to effectively kill weeds.

“A considerable amount of research goes into understanding what our full 1X use rates should be that are listed on our product labels,” says Mark Kitt, corn herbicide technical product lead at Syngenta. “Using the full rates for resistance management is important because lower rates sometimes create a potential resistance management issue.”

If you apply less than the labelled rate, weeds are exposed to a potentially effective herbicide, but at a sub-lethal level, which the weed’s enzymes may overcome. This increases the likelihood of future resistance issues.

Preemergence residual herbicides offer some hope in the face of metabolic resistance challenges. After all, the best time to control weeds is before they emerge.

“That’s one reason we still see effectiveness with the preemergence residual herbicides,” Palmer says. “They’re controlling a germinating seed, before that metabolic engine really gets going in a larger weed with a buildup of enzymes that break down herbicides.”

Herbicide Recommendations for Your Corn, Soybean and Cereals

Palmer says the feedback on Tendovo^® preemergence residual herbicide in soybeans has been very positive. He recommends it for its three sites of action and the robust amounts of active ingredients built into the formulation. “One of the components is metribuzin, for which there’s no documented Amaranthus resistance at this time,” he says. “So, it gives you a really solid foundation for your soybeans.”

Kitt points to Storen^® and Acuron^® corn herbicides and stresses that they’re put out in fields before weeds emerge, whether that is at planting or even before planting. Both Storen and Acuron can be applied as early as 28 days preplant. With four effective active ingredients and three sites of action, Acuron is the top solution for resistance management, controlling the toughest broadleaf weeds and grasses. The four powerful residual ingredients in Storen deliver unprecedented weed control — with 95% control in 9 out of 10 fields.²

For post-emergence residual applications, Kitt reminds applicators to keep water volume up, speed down, and use proper adjuvants and nozzles. With Acuron GT postemergence corn herbicide, he says the most important thing is to be sure it’s applied to weeds less than four inches in height.  “Get out there when those weeds are small,” he says. “Better yet, make residual herbicide applications before weeds have emerged. That’s the best way to keep resistance in check.”

Currently, herbicide resistance recommendations in cereals are complicated. Belles, who is also the Chairman of HRAC, refers to a North Dakota survey showing that resistance to Axial^® Bold or Axial Star cereals herbicides is lower than some of the other products being used. He suggests collecting and testing weed seed from your fields to determine which chemistries are most effective on those populations.

Managing herbicide resistance in 2026 won’t be easy, but thoughtful planning and consideration will make it easier. Understanding resistance mechanisms, using full labelled rates and prioritizing strong preemergence programs are crucial for continued success. Arm yourself with knowledge and the right tools, then execute the plan that makes sense for your fields.

¹ Heap, I. The International Herbicide-Resistant Weed Database. www.weedscience.org. 

²Data Source: HBI003A4-2022US – (15 locations, 30 weed data points). Rates tested: Storen 2.4 qt/A + AAtrex 0.75 qt/A, Resicore^® 3 qt/A + AAtrex 0.75 qt/A.