How to Manage Herbicide-Resistant Weeds

Herbicide-resistant weeds can turn a manageable field issue into an expensive, season-long challenge. Starting clean, using multiple effective modes of action and building residual control into the herbicide program can help protect yield and preserve weed-control options.

What Are Herbicide-Resistant Weeds?

By definition, herbicide resistance “is the ability of a weed biotype to survive a herbicide application, where under normal circumstances that herbicide applied at the recommended rate would kill the weed” (HRAC 2026).

Several troublesome weed species in the United States have developed resistance to multiple herbicide modes of action, including:

• Italian ryegrass
• Kochia
• Palmer amaranth
• Barnyardgrass
• Jungle rice
• Horseweed

Why Is Herbicide Resistance Increasing?

Herbicide resistance existed before glyphosate-resistant crops were introduced in 1996. However, the adoption of crops that allowed over-the-top glyphosate applications changed how many weed-control programs were built. In some production systems, diverse herbicide programs shifted toward repeated use of a single broad-spectrum mode of action.

Weed management programs that depend heavily on one postemergence herbicide place continued selection pressure on weed populations. Susceptible weeds are controlled, while plants with resistance traits may survive and reproduce.

How Widespread Are Herbicide-Resistant Weeds?

The International Herbicide-Resistant Weed Database reported 540 unique cases of herbicide-resistant weeds globally. The database also reported resistance to 21 of the 31 known herbicide sites of action, involving more than 160 weed species across 100 crops. [weedscience.org]

How Herbicide-Resistant Weeds Affect Yield and Costs

Herbicide resistance can increase weed-control costs, complicate application timing and expose crops to damaging early-season competition.

In herbicide costs we see as much as a 3x increase in weed management cost in certain crops due in a large percentage to herbicide resistance.

Uncontrolled early-season competition from herbicide-resistant weeds can reduce yield by 20% to 60%, depending on the crop and weed biotype. Severe infestations may lead to the loss of part of a field or, in extreme situations, an entire field.

Once resistant weeds are established and growing, control options may be more limited. Residual (preemergence) herbicide programs greatly offset the cost, challenges, and impacts HR weeds impose while providing positive ROI on crop protection.

8 Ways to Manage Herbicide-Resistant Weeds

An effective herbicide-resistant weed management program should not depend on one product or one application. Instead, it should combine chemical, cultural and mechanical practices that reduce weed pressure and limit the opportunity for resistant plants to survive.

1. Start With a Clean Field

Control emerged weeds before planting. A clean start reduces early competition and gives the crop a better opportunity to establish.

2. Use an Effective Preemergence Herbicide

Choose a preemergence herbicide that is appropriate for the crop, target weeds, soil conditions and field history. Preemergence herbicides can control weeds before they compete with the crop.

3. Include Multiple Effective Modes of Action

Use herbicide modes of action that are effective against the target weed species. Simply including several active ingredients does not provide a resistance-management benefit if only one is effective on the weed being controlled.

4. Layer Residual Herbicides

Where appropriate, use overlapping residual herbicides to extend control and reduce additional weed emergence later in the season.

5. Apply Herbicides at the Right Time and Rate

Apply herbicides when weeds are at the growth stage listed on the label. Always use labeled rates and follow all product directions.

6. Scout Fields Early and Often

Watch for surviving weeds, unexpected control patterns and new infestations. Documenting where escapes occur can help guide future weed-management decisions.

7. Add Cultural and Mechanical Practices

Crop rotation, tillage and other management practices can reduce reliance on herbicides alone. The right combination will depend on the crop and production system.

8. Prevent Weed Seed Production

Control escapes before resistant weeds produce seed. Preventing seed production can help reduce the number of resistant weeds entering the soil seedbank.