Weed control in soybeans: How to win the battle in 2024

By David Kee, SSGA Agronomy action team Staff Lead/Director of Research, Minnesota Soybean Research & Promotion Council

Herbicide resistant weeds have taken the stage in the continued doom and gloom stories from the popular press. However, those articles forget that weed control is – and always has been – a constant battle in agriculture. I remember stories from my grandfather of a 12-year-old boy thinking the 1916 battlefields of Europe couldn’t be any worse than “choppin’ cotton” in the sweat-soaked environment of a mid-July east Texas cotton field.

At one time, quackgrass was one of the primary weeds in short stature crops (soybeans, etc.), as it was, and still is, extremely tolerant of any mechanical weed control method. Modern weed control efforts have reduced its impact, but that doesn’t mean quackgrass has gone away. It is just under control using our current technology. Literature from the 1960s indicates waterhemp was a minor weed problem; today, it is a major headache for identity preserved (IP) producers.

What is the take-home message? Weed control is always evolving. Proper identification of the problem and providing an adaptable management program are critical to success. A good manager starts with the basics, and then develops a creative solution to that ever-independent world called “their farm.”

What are the basics?

1. Scout in the fields. Know your fields, know your crop and know your weeds. Assess the fields for weeds, and other problems, as often as possible. There is no such thing as excessive effective crop scouting. However, ineffective scouting wastes time, money, energy and effort.
2. Effectively change management. Rotate crops, rotate chemistry, add some forms of mechanical weed control and include cover crops. Don’t do the same thing every time, as that will allow some pest to evolve around a management system.
3. Scout the perimeter of your fields. Look beyond your field. Are there weeds in the ditches, along the fence line, on your tractor tire, in your combine? Institute effective sanitation activities, mow the buffer area enough times to prevent problem weed from going to seed, amp up the weed control efforts on those rows bordering weed infested areas.
4. Be effective. Develop and institute an effective weed control program, use both pre and post-emergent herbicides at full recommend rates in a system that rotates Sites of Action (SOA). Remember, Muhammad Ali hit his opponent everywhere, not just on the chin. You have to change up the punches to keep taking out those weeds. Think both strategically and tactically; creative effectiveness becomes critical for success.
5. Scout for future years. Look back at what you’ve done; think about what you will be doing. Sometimes the best place to scout is at your desk reading your farm diary and contemplating your next step. Ask if your management program worked? If not, why not? What needs to be done next? Scout after canopy closure, the canopy will open again after growth stage 7 as the crop matures, waterhemp and other season-long germinating weeds will pop up and require control efforts.
6. Be persistent. Weed control is not a once-a-year activity. There is always more than one species of weeds present, weed seed germination is complex and often unpredictable. To be effective over the long run, adopting a zero-tolerance goal will go a long way toward keeping a grower on top of the problem. Keep a diary of activities, review it often and ask yourself if you are being effective? What can be done better? What are you giving up by not controlling any pest at certain times? No decision is trivial and should be approached in a logical manner. Knee-jerk reactions tend to be ineffective.

As with any management program, the basics are just that: the basics. A one-size-fits-all program usually results in a poorly fitted suit. Educate yourself. Use the Take Action on Weeds website developed by the United Soybean Board and weed scientists from 10 states. It provides you with a bounty of information on weed species, herbicide modes of action and will help you create an herbicide plan of action for your farming operation.

The program you develop should be tailored to your individual operation. Talk with Extension, other farmers, your local crop consultant and any other professional whose judgement you trust and develop an effective solution for your operation. Then change it up somewhat from year to year. To be effective, you must evolve as the weeds evolve.