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WEED BREAKOUT: Wild oats push a wheat crop canopy. Some wild oats may be resistant to commonly used herbicides.

10 steps to combat herbicide resistance

Don’t wait for resistant weeds to appear on your farm.

If you wait for resistant weed populations to appear on your farm, you can expect them to quickly spread across entire fields. But by employing comprehensive management techniques early and continuing them throughout the season, you can fight the onset of resistance.

I recommend these 10 steps:

1. Start with clean fields and apply a burndown herbicide to help control emerged weeds before planting.

2. Plant rotation crops to extend the range of available herbicides and agronomic practices.

3. Scout fields early and often to correctly identify weeds and select a product that addresses each field’s specific weed spectrum.

4. Employ multiple modes of action by using a tankmix at each application during the growing season. This will reduce the selection pressure caused by using a single mode of action.

5. Keep fields clean by using residual herbicides so young wheat plants can absorb sun, water and nutrients without competition from weeds.

6. Apply herbicides at full, labeled rates and at the correct growth stage for effective weed control.

7. Use effective adjuvants to improve herbicide efficacy.

8. Closely monitor problem fields, identifying difficult-to-control weed species and dense weed populations.

9. Clean equipment as machinery can easily spread seed from one field to another.

10. Evaluate weed management results at the end of each harvest to improve weed control for the next season.

Follow these steps and it will help ensure that you have quality, productive wheat fields with high-yield potential at harvest.

What is herbicide resistance?
Although many believe it to be a complex, intimidating topic, herbicide resistance can be simple to explain. It occurs with repeated use of a specific herbicide or a combination of herbicides in an effort to control a population of weeds that contain some plants with resistant genes.

There are two broad categories of herbicide resistance — target site and metabolic.

Target site resistance is more common and occurs when the weed population has changed and will no longer allow the herbicide to attach to the target site, making the chemical ineffective regardless of the rate used. Target site resistance is specific to a particular site of action.

Metabolic resistance occurs when the plant produces an enzyme that breaks down the chemical before it can kill the weed. When products are used below label rates, the risk of developing metabolic resistance will increase. For example, some ryegrass can be resistant to ACCase, ALS and photosystem II inhibitors.

According to The International Survey of Herbicide Resistant Weeds, there are 13 herbicide-resistant broadleaf and grass weed species found today in U.S. wheat crops. In particular, wheat growers have observed widespread occurrences of herbicide-resistant kochia and wild oat.

Popiel is the Syngenta agronomic service representative in North Dakota. For wheat agronomy tips, email nathan.popiel@syngenta.com.

TAGS: Herbicide
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