Agronomy Talk


Published on Tuesday, November 10, 2020


  1. Power in the PRE™. Post-emergence control options are much more limited in non-GMO soybeans.

  2. The success of a PPO post-emerge herbicide will be influenced by weed size and densities.

  3. Options become much more limited if you suspect the population to be resistant to non-GMO post-emerge herbicides.

To be successful in non-GMO soybeans fields, especially those with weeds resistant to multiple herbicides, apply the same management principles as GMO soybeans. These principles become more critical with non-GMO soybeans because rescue options are much more limited. Just like any GMO platform, the power is in the pre-emerge, and the best weed to control is one that never emerged. PPO post-emerge herbicides such as Cobra®, Flexstar®, etc., are effective on waterhemp that is less than 4 in. tall, but some populations have become resistant. Group 2 herbicides like Classic® and FirstRate™ have post-emergence activity on large-seeded broadleaf weeds such as morningglory and cocklebur. For susceptible giant ragweed populations, Group 2 herbicides will have effective post-emergence and residual activity. For grass control, clethodim or other Group 1 herbicides can provide very effective control. Success in the post-emergence trip depends on the susceptibility of the population; therefore, the best insurance policy is to never let the weed emerge.


In 2020, Beck’s PFR looked at various herbicide programs in non-GMO soybeans. For the pre-emerge application, Authority® Supreme was very effective on waterhemp and grasses. Authority Supreme utilized two “effective” SOAs, reducing the number of emerged weeds in the post-emerge application. Flexstar and Cobra provided post-emergence activity on waterhemp that was less than 4 in. tall. However, some waterhemp populations have become resistant to Group 14 herbicides, which are also weak on grass so an addition of clethodim was critical. Beck’s 2020 PFR data showed PPO post-emerge herbicides resulted in less than 73% control of waterhemp, which may have been impacted by the thick vegetation and poor coverage. The successful pre-emerge application helped the post-emergence trip be much more successful and allow greater coverage. The addition of Warrant® to Cobra provides another layer of protection in-season, and Warrant® Ultra, a Group 14 + 15 herbicide, will have both post-emergence and residual activity. If you suspect PPO-resistant waterhemp in your field, then an in-season residual becomes even more crucial in the hopes that it will allow enough time for the crop to reach canopy closure. Once we reach canopy closure, the shade will make it much more difficult for weeds to emerge. By the end of the season, treatments with Warrant had less escapes compared to treatments without an in-season residual. 


Authority® Supreme did an excellent job reducing the number of weeds that the post-emergence herbicide had to control. In-season residuals are critical, especially if you suspect the population to be resistant to non-GMO post-emerge herbicide options like Flexstar® or Cobra®. In-season residual applications must be made before the pre-emerge herbicide breaks. Clethodim provides effective grass control.

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Author: Joe Bolte

Categories: Agronomy, Agronomy Talk


Joe Bolte
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