We all want a lush, green lawn free from unsightly weeds. But a silent battle is being waged in our turfgrass, threatening the effectiveness of our weed control efforts: herbicide resistance. This isn't just a problem for golf courses or sports fields; it affects homeowners, too. This information will explain herbicide resistance, why it's happening, and most importantly, what you can do about it.

What is Herbicide Resistance?

Imagine a population of weeds. Most are susceptible to a particular herbicide, but a few, due to natural genetic variation, can survive its application. When you repeatedly use the same herbicide (or herbicides with the same mode of action – MOA), you kill the susceptible weeds, leaving the resistant ones to thrive, reproduce, and spread. Over time, the resistant population dominates, rendering the herbicide ineffective. This is herbicide resistance in action.

Why is This Happening in Turfgrass?

Several factors contribute to this problem:

• Over-reliance on Herbicides: We often turn to herbicides as the sole solution for weed control, neglecting other essential practices.

• Lack of MOA Rotation: Using the same herbicide or herbicides with the same MOA repeatedly accelerates the development of resistance. Think of it as taking the same antibiotic too often – eventually, it stops working.

• Limited New Herbicides: The development of new herbicides with novel MOAs has slowed in recent years, limiting our options for rotation.

What Can You Do to Fight Back?

The good news is that you can take proactive steps to mitigate and delay herbicide resistance in your lawn:

1. Promote a Healthy Lawn: A dense, healthy turf is the best defense against weeds. This means:

   • Choosing the right grass type for your climate.

   • Proper fertilization and irrigation.

   • Mowing at the correct height and frequency.

   • Regularly scouting for and addressing diseases.

2. Implement Integrated Weed Management (IWM): Don't rely solely on herbicides. IWM involves using a combination of strategies:

   • Preventative: Using weed-free seed, cleaning equipment, and maintaining healthy turf.

   • Mechanical: Hand-pulling weeds, mowing, and core aeration.

   • Cultural: Proper watering, fertilization, and mowing practices.

   • Chemical: Using herbicides strategically and responsibly.

3. Rotate Herbicide MOAs: When you do use herbicides, it's crucial to rotate between products with different MOAs. This prevents weeds from developing resistance to a single type of herbicide. You can find information on herbicide MOAs on product labels or through resources like university extension websites.

4. Use Multiple MOAs Within a Season: Consider using both pre-emergent (PRE) and post-emergent (POST) herbicides with different MOAs. PRE herbicides prevent weed seeds from germinating, while POST herbicides kill existing weeds.

5. Use the Correct Herbicide Rate: Applying too little herbicide can lead to incomplete control and contribute to resistance development. Always follow label instructions.

6. Ensure Optimal Environmental Conditions: Herbicides work best when applied under the right conditions. Consider factors like temperature, moisture, and soil conditions.

Is it Resistance or Something Else?

Sometimes, a herbicide application might fail for reasons other than resistance. Consider these factors:

• Application Timing: Was the herbicide applied at the correct time, especially for PRE herbicides?

• Environmental Conditions: Were conditions favorable for herbicide activity?

• Rainfall or Irrigation: Did heavy rain or irrigation wash away the herbicide?

• Soil Conditions: Were soil conditions optimal for herbicide activity?

If you've ruled out these factors and still see poor control, especially if you've used the same herbicide repeatedly, resistance may be the culprit.

What if Resistance is Confirmed?

If you suspect or confirm herbicide resistance, act quickly:

• Switch to a different MOA: If possible, use an herbicide with a different MOA that is effective against the resistant weeds.

• Consider other control methods: Hand-pulling, mechanical removal, or even lawn renovation may be necessary.

Call to Action:

Don't wait until herbicide resistance becomes a major problem in your lawn. Take proactive steps today:

• Learn about Integrated Weed Management: Research IWM practices and implement them in your lawn care routine.

• Understand Herbicide MOAs: Familiarize yourself with different herbicide MOAs and rotate them effectively.

• Consult with a Turfgrass Professional: If you're unsure about the best approach for your lawn, seek advice from a qualified professional.

By taking these steps, you can help protect the effectiveness of herbicides and maintain a healthy, weed-free lawn for years to come.