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Managing Weed Resistance

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April 5, 2018
Ryan Ponwith
Master Field Sales Agronomist
Herbicide resistant weeds have rapidly evolved into a major threat to agricultural productivity. Globally, 254 weed species have evolved resistance to 23 of the 26 known herbicide sites of action. Many of these weed species are resistant to more than one site of action. Additionally, no new herbicide sites of action have been introduced since the 1980’s. Combating these resilient weeds is going to take effective herbicide plans and excellent execution in the field.
 

How Can I Control Resistant Weeds?
When putting together your 2018 herbicide plan, follow a few basic rules to be successful in limiting weed pressure:
  • Include a soil-applied residual herbicide with your post-application
  • Utilize a minimum of 3 herbicide sites of action
  • Understand the characteristics of your problem weeds
 
Stop Weeds Prior to Emergence
The simplest way to stop weeds is to kill them prior to emergence. Soil-applied residual herbicides work to stop weed seed germination by limiting shoot or root growth. Use these products as a tank mix partner with your post-herbicide application to get your crop to canopy with limited weed emergence.

Waterhemp is known for having a wide emergence window that spans a large portion of the growing season. Seeds will begin to emerge in the middle of May, peaking in July, and finally trailing out into the end of August. Residual products will provide a longer control window, helping the crop to reach canopy before most waterhemp seeds emerge. This allows you to focus on eliminating weed seed buildup in your fields.


Understanding the biology of waterhemp and its emergence characteristics is one example of the importance of knowing how weeds behave. By knowing these characteristics, we can make better management decisions to limit their negative impact on profitability.

Avoid Selecting for Resistance
A herbicide plan that lacks diversity in the chemistries used will promote quicker development of herbicide resistance. Practices that stimulate the development of resistance are:
  • Herbicides that act on a single site of action
  • Herbicides that are applied multiple times during the growing season
  • Herbicides used for several consecutive growing seasons on the same field without rotation
To limit selection pressure on one specific herbicide or site of action, utilize at least 3 herbicide sites of action throughout the growing season, not including Roundup. An example of a herbicide program for soybeans utilizing 3 to 4 effective herbicide sites of action is shown above.

In this example, taking advantage of the Xtend crop system allows us to employ 4 effective herbicide sites of action. Not including Roundup as an effective site of action, you will be attacking weeds with Group 2, 4, 14, and 15 herbicides by using this soybean plan.

Prolific weeds are driving decisions in 2018. By including a residual herbicide, multiple effective sites of action, and taking the time to learn about our weed opponents, your 2018 herbicide plan will be effective in controlling weeds and limiting the development of additional herbicide resistance.

Contact your local Field Sales Agronomist at UFC to put the finishing touches on your 2018 herbicide plan.