Agronomy Talk

WEED MANAGEMENT BRIEF: INFLUENCE OF WEED SIZE ON LIBERTY APPLICATIONS

Published on Tuesday, October 20, 2020

 

ABSTRACT:

  1. Liberty® is very effective on glyphosate-resistant weeds like waterhemp, marestail, and giant ragweed. For greater efficacy, target weeds less than 4 in. tall.

  2. If weeds become too large, Liberty® control will be reduced.

  3. Spraying large weeds will result in reduced control, increasing the chance of resistant weeds.

 

WHY DOES WEED SIZE MATTER?

Contact products like Liberty® require proper coverage to achieve successful weed control. One factor that will influence coverage is the carrier rate. Beck’s Practical Farm Research (PFR)® data shows a 12% increase in waterhemp control when Liberty is sprayed at 20 GPA vs. 15 GPA. Contact herbicides do not move in the plant like a systemic herbicide such as glyphosate does. Therefore, control will be heavily impacted if a contact herbicide does not cover the entire plant.

Another factor that can impact coverage is weed size. If weeds become too large, it will be much more difficult for contact herbicides to cover the entire plant. Therefore, controlling weeds when they are less than 4 in. tall is key for a successful application. Liberty grass control is weaker compared to glyphosate, which will be magnified if applications are made to grasses taller than 4 in.

2020 RESULTS

Glyphosate grass control was not as heavily impacted by weed size. However, we still must spray weeds when they are small to ensure greater efficacy. The waterhemp population was suspected to be resistant to glyphosate; therefore, only the fall panicum was controlled. 

Liberty resulted in excellent waterhemp and fall panicum control when weeds were 4 in. or less in height. However, control was greatly reduced when applications were made on weeds that exceeded 4 in. tall. When adding glyphosate to the tank, it can help increase Liberty grass control as well as other susceptible broadleaf weeds. However, if weeds become too large, we can start to see antagonism, especially when spraying grasses.

As we move forward with various tank mixes, it’s important to consider antagonism, which will be magnified on larger weeds. Spraying weeds when they are small will help increase the efficacy of the application which results in less weeds in the seed bank. Spraying weeds that are too large will not only result in poor performance but also promote resistant weeds.

CONCLUSION:


Antagonism is magnified when herbicide applications are made to large weeds. No matter if the product is contact or systemic, it’s vital to target small weeds. Liberty is very effective, but we must ensure proper coverage.

 

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Author: Joe Bolte

Categories: Agronomy, Agronomy Talk

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