Some have had challenges, but all will have weeds
It is only the beginning of June, but with all of the curveballs thrown our way this early in the growing season, it feels much later. If these "curveballs" aren't registering with you, consider yourself lucky! There have been cutworms, armyworms, slugs, millipedes, stripe rust, hail, significant corn and soybean replant, and precipitation measured in feet. With all of these challenges, I have learned two things: crops are remarkably resilient, and so is the American farmer. However, there has already been enough stress—for the crop and the farmer—to last the entire season. With this in mind, one question remains: are there any foreseen challenges on the horizon that can be mitigated before they result in additional stress and yield loss to our crops?
As the growing season continues, we will all inevitably face an abundance of weeds, especially in soybeans. If we manage these weeds correctly, we can minimize stress to the soybeans, preserve yield, and reduce the weed seedbank all at the same time. In order to accomplish this mission, we need to follow these three steps: choose the correct herbicide, spray small weeds, and use overlapping residuals.
Step 1. Choose the correct herbicide. Glyphosate has been a great tool to help us manage weeds for the last two decades in our soybeans. Unfortunately, many of our tough to control weeds, including waterhemp, are resistant to glyphosate. This means we need to focus our attention to a herbicide mode of action that will effectively manage the weed species that are present. In the case of waterhemp, this may mean using a PPO-inhibiting herbicide, such as Flexstar® or Cobra®. Liberty® can also be effective in LibertyLink® soybeans. This year we also have a new technology available in the Roundup Ready 2 Xtend® soybeans that allows for in-crop use of specific dicamba-containing products; the products approved for this use pattern are XtendiMax™, Engenia™, and FeXapan™. Regardless of the product or technology that is chosen, make sure it will effectively control the target species.
Step 2. Spray small weeds. Trying to kill a two foot tall weed with herbicide is the equivalent of taking a knife to a gunfight. You will lose most of the time! Not only has that tall weed already taken up the light, water, and nutrients that were meant for the soybean crop, but now it will be almost impossible to kill. Most herbicides will recommend that weeds be sprayed prior to reaching four inches in height. This is a good target that will provide the highest probability of success.
Step 3. Use overlapping residuals. Because our weed spectrum has been so difficult to manage, we are now relying on pre-plant and pre-emergence residuals. This is a good practice! In addition to these early season residuals, we need to consider overlapping residual herbicides. The best defense against weed emergence is the crop canopy; however, it is going to be a long time before soybeans canopy. An overlapping residual herbicide applied during the post-emergence application will bridge the gap from the time of application to crop canopy and allow for a greater chance of the field to be weed-free. Group 15 herbicides, such as Dual Magnum®, Outlook®, Warrant®, and Zidua® are commonly used in emerged soybeans to provide overlapping residual activity.
Following these steps are important to ensuring successful weed control in soybeans. In addition, there are several intangible items and information that can swing the odds in your favor. This includes, but is not limited to: choosing the correct herbicide rate, spray volume, adjuvant, and time of application.
Contact your local FS Crop Specialist to help develop a weed management plan that works with your operation.
Dr. David Powell serves the FS System as GROWMARK Weed Science Technical Manager. He can be reached at [email protected].