Palmer amaranth is beginning to emerge throughout the Corn Belt. That means it’s time to scout your corn and soybean fields for this weed, as well as common waterhemp, kochia, marestail and velvetleaf.
In most cases, a post-emergence residual herbicide program should be applied within 10 days of identifying the weed in your field. Ideally, post-emergence herbicides should be applied to bare ground, so they are overlapping with your pre-emerge residual herbicide application, and before you see any weed emergence.
What type of weed control works
Most foliar herbicide treatments in corn will include a Group 4 herbicide (Growth Regulator), for example dicamba could be used for broadleaf weed escapes, and they often include glyphosate for added broadleaf and grass control. Growth regulators are absorbed by plant leaves and roots. Post-emergence treatments should also include a residual herbicide product to achieve season-long weed control.
Group 15 (Long Chain Fatty Acid Inhibitor), such as Dual MAGNUM® or Zidua® Herbicide are commonly used for this purpose. These residual herbicides are active on plant shoots and roots, but not plant leaf tissue. This means they will have little to no impact when applied to growing weeds.
With new technology, you now have a dicamba-tolerant soybean option that can be treated with Xtendimax® With VaporGrip® Technology or Engenia®. These two products contain a safened dicamba herbicide. There are many new rules and regulations concerning application and recordkeeping with these new herbicides—the applicator must attend a class and be trained on how to properly apply these products.
Watch for weed escapes and consider timing
When you are treating weed escapes, be aware of the weed size in inches at the time of application.
Why? Because some herbicides will say on the product’s label that they control weeds up to 6 inches tall, while other herbicide product labels are intended only for weeds that are up to 4 inches tall. But consider this—palmer amaranth can grow up to 4 inches a day once it reaches 6 inches in height.
Most foliar herbicide complaints around efficacy occur when weeds were treated at a height larger than the product’s label recommends, and that causes poor control of the target weeds. This is not a product failure, and that’s why application timing is important to achieve the weed control you’re looking for.
You might be interested in our February survey where we asked FBN network farmers, “What percentage of your 2017 planted acres were resprayed due to product performance where the manufacturer reimbursed you for product cost?
More than 1,500 network-members across the U.S. responded to our poll.