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In the past, it was common to use herbicides that do NOT provide residual control for controlling weeds in soybeans. With the most popular herbicides we had at that time, we could let weeds grow and then control them with multiple herbicide passes. Today, with herbicide resistant waterhemp, I would suggest that we cannot allow waterhemp to even emerge from the ground because we cannot rely on those herbicide sites of action anymore. Therefore, I am promoting a “never see a weed in your field” philosophy of weed control in soybeans. Here is my definition of this philosophy:

 

“Using rates of multiple site of action pre-emergence residual herbicides that are still providing residual control of weeds PAST the proper timing of the post herbicide treatment. The pre herbicide should also contain multiple sites of action products that provide residual control of weeds.”

 

Below are the herbicide sites of action that are available both pre and post in soybeans:

Pre-emerge	Common brand names
Group 2 ALS Group 3, DNA's Group 4 Growth Regulators Group 5 Photosystem II Group 9 Group 14 Group 15	Classic®, Pursuit®, Pinnacle Treflan®, Sonalan® Dicamba, 2,4D Metribuzin EPSP, Roundup® Authority®, Valor® Warrant®, Dual®, Outlook® and Zidua®
Post-emerge	Common brand names
Group 1 ACCAse Group 9 Group 4 Synthetic auxins Group 10: Glutamine synthase Group 14: PPO	Select Maxx®, Fusilade® (All soybean traits) EPSP, Roundup® (Roundup Ready® Soybeans) XtendiMax® (Roundup Ready 2 Xtend® Soybeans), 2,4D (Enlist® Soybeans) Liberty® (LibertyLink® and Enlist) Flexstar®, Cobra® (all soybeans)

I recommend utilizing as many herbicide sites of action as possible pre-emergence, especially in non-GMO soybeans. Why? Because in non-GMO soybeans you only have 1 herbicide SOA (site of action) that can be used post-emergence, Group 14 PPO. Remember that we have many PPO resistant waterhemp. This means we need to stop as many waterhemp as we can from emerging by utilizing multiple herbicide sites of action pre-emergence.

 

Even though waterhemp is resistant to the Group 2 ALS site of action, I like Classic or Pursuit in a soybean pre-emergence herbicide, as I feel this chemistry helps us reduce the amount of larger seeded broadleaves like velvetleaf and giant ragweed that germinate. We can then address what does emerge later with a post-emergence application. 

 

For post-emergence applications, I recommend using every herbicide SOA available in whatever trait you have purchased (for example utilizing Xtendimax and Roundup in Roundup Ready 2 Xtend soybeans), plus the addition of a group 15 product for extended residual post-emergence.

 

Your crop protection retailer is the expert source for questions about what herbicide sites of action you plan to use in soybeans for 2019. Make sure they have you well covered.