When looking for a soybean residual herbicide program, I have yet to find one that is a silver bullet for every weed across the board. In my experience, it is harder to select a broad-spectrum soybean herbicide than a broad-spectrum corn herbicide. For a soybean weed control program to work, you have to know what you are fighting against. In a corn weed control program, you can take a more general approach and get by. You need to get your boots dirty and figure out what weeds you have—and also figure out if the tool you used works.
At this point in mid-May, most soybean fields have—or should have had—a soil-applied residual herbicide applied as the first step of a weed control program. Most soybean residual products have strengths and weaknesses. We generally combine two active ingredients to create the products we use today, and by combining two products we are attempting to shore up any weaknesses that may exist with the companion product. However, most of these products still contain gaps that can create issues.
Before taking the next step and making a post-herbicide application, you need boots on the ground to plan your next strategic attack. About 3 – 4 weeks after a residual application, you should be able to see if there are weaknesses in your soybean residual program. If you apply a blanket approach to all of your fields by making general assumptions, there may be weed species that you will miss with your post application. If a weed sneaks by your residual application—and is not controlled in your post application—chances are that weed will not be controlled again this season. It will most likely have grown to a size that can only be controlled by a good ol’ fashion walking crew. At that point you have damaged your yield and will take a serious hit to your profit per acre—with the added expense of removing weeds.
This boots on the ground statement actually means stopping the truck and getting out into the field. The days of scouting from the pickup for green between the rows are gone. Weed identification is going to become more important to figure out what your strategy will be for the next application. You can also take notes on what weed species are still present, allowing you to select a different herbicide with different strengths in the future.
I recommend working closely with your local Certified Crop Advisor to review the efficacy of your program and to confirm that your next step is a sound one. That will put your soybean fields in a position for success.
Adam Day is a Certified Crop Advisor working with Northern Partners Cooperative in Ottawa, Illinois, as an Agronomy Account Manager. He works directly with growers on a daily basis, providing them with information and services to help them make decisions in their operations. His goal in working with farmers is to have a partnership to increase yield, profitability and sustainability.