Adjusting Herbicides for Better Control

Aerial Photo of Combine


This past year has again been a challenge with the continued drought and the advancement of HPPD-resistant waterhemp in corn. If you’ve felt this pressure in your own fields, we see two areas you can confidently make changes when preparing for 2024.

The first place to start when investing in a better herbicide program is to take a look at your current pre rates. How much residual are you actually applying?

Corn pre’s at full labeled rates should give about eight weeks of residual control. For example, a standard full rate of Harness Xtra on medium to fine soil is 2.3 quarts and should give you that eight weeks of control. If a grower is applying a reduced rate of 1.5 quarts of Harness Xtra, actual residual applied is about 65% of a full rate of acetochlor, which only provides roughly five weeks of control. If the application rate is increased to 1.8 to 2 quarts, the length of residual should increase to 6 to 7 weeks respectively.

The second area adjustments can be made is in your post tank mix. Resistance to Callisto, Laudis and Impact is showing up in more corn fields. Therefore, in addition to stronger pre’s we need to look at adding modes of action to your post pass in corn. This would include dicamba (if less than V3), Diflexx, Tough and Status.

Third passes are hard to make in corn when height and coverage becomes an issue. Tall corn spraying then becomes a rescue mission with usually less-than-desirable results. The best solution is a proactive program with stronger pre’s and enhanced post tank mixes.


In soybeans, we are placing waterhemp selection pressure on our growth regulators in our post applications. These products include Extendimax, Engenia,
and Enlist. To reduce this selection pressure, residuals again are the first place to start looking at.

A full rate of one active ingredient is better than a reduced rate of one active ingredient pre followed by a reduced rate of another active ingredient post.

For example – if you apply a pyroxasulfone (Zidua) based pre, it would be most advantageous to follow that pre application with more pyroxasulfone in your post tank mix rather than using another Group 15. This logic should be used with other Group 15’s used pre emerge as well.

As most have seen over the past few years, 2,4-D is less effective on waterhemp than dicamba. To maintain the Enlist technology, the best recommendation for post applications in Enlist soybeans is to add Liberty to the Enlist tank mix. Liberty and Enlist compliment each other and give us two effective modes of action for better control of waterhemp than either product sprayed alone. A post residual added to this recommendation makes this program even stronger. With the lower cost of Liberty in 2024 this could be a viable option for our growers.

We remain concerned about more restrictive label changes to Xtend soybeans. If more restrictions are imposed, the only logical use for Xtendimax, Engenia or Tavium would be to add it to our pre herbicides to help burn down germinating waterhemp and give us a bridge until our pre herbicides are fully activated.

Liberty will then be our only effective product to control waterhemp post emerge
in ExtendFlex soybeans. If this occurs, we then need to use higher rates and it becomes imperative to include a Group 15 residual to provide enough control until canopy.

In addition to higher pre rates and multiple modes of action post, there are other controllable factors that can improve weed control with little cost involved.

1. Apply product with the correct water volume

Most manufacturers encourage higher water volumes in post applications for better
coverage and better control. Enlist, Xtendimax, Engenia, Liberty and Tough are all going to work better with 20 gallons per acre than 15 gallons per acre. Callisto, Laudis and Impact/Armezon will all work better with 15 gallons per acre versus 10 or 12.

2. Use product specific tips

A TTI tip that was approved for Xtendimax/Engenia will result in poor performance if used for Liberty, Enlist or Callisto.

3. Add Atrazine to your HPPDs

Atrazine synergizes the HPPD’s. Adding as little as a quarter pound per acre can give you better control than leaving it out.

4. Apply with the best adjuvant

If a product can be used with NIS, COC or MSO, chances are the weed control will be improved using COC or MSO versus NIS. An example of this is with Diflexx or Status. All three adjuvants are labeled for both products, but better weed control will come from using COC or MSO rather than NIS.

As you can see, there are many strategies to employ for 2024. All it takes is a little proactive planning. Look to a Wells Ag Supply agronomist for the most up-to-date, unbiased information as you prepare for this coming season.

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