No matter the growth stage, soybean weeds are never a welcome presence. In fact, early-season weed control is critical to minimize direct competition with weeds that emerge at about the same time as the crop.
If weeds do escape through your pre-emerge herbicide program, the earlier you can identify and control these weeds, the better your chances are of keeping costs low and yields high.
Soybean weeds with early germination times include:
- Waterhemp: Waterhemp can emerge anywhere from mid-May to late July. Waterhemp’s delayed emergence is problematic, allowing it to avoid earlier weed control tactics, making post applications especially critical.
- Common lambsquarters: This early-emerging species appears at the beginning of the season and continues into the summer, with one of the longest emergence durations of all weeds.
- Kochia: Kochia is an early germinator, but some plants do germinate continuously during the growing season, beginning in March, with the last flushes occurring from August to early September.
- Giant ragweed: Recent research shows that giant ragweed can begin emerging as early as March.¹. Most of the annual emergence will occur in the first two to three weeks of spring.
To make matters worse, no-till operations must also keep an eye out for winter annual weeds like marestail that create early-season competition for soybean plants.
Timing for early spring weed control
Research concludes that controlling soybean weeds before they reach a height of 6" to 8" successfully protects yields.²
However, the key window of control varies widely depending on factors like weed species, weed densities, environmental conditions, and cultural practices in play.
Keeping the field clean will help soybean crops canopy sooner, hampering the growth of early-season weeds.
Most effective soybean weed control protocol
It’s tempting to skip the early-spring weed control for the sake of saving time and labor, relying on post-emergence herbicide applications to do the job later in the season. However, managing early-season weeds in soybeans can increase the efficacy of post-emergence herbicides by reducing weed populations and knocking out early emerging weeds that would in turn end up too big for a successful post application.
The most effective strategy is to overlap pre-emergent soybean herbicides, providing protection from both early- and late-emerging weeds.
Using Outlook® herbicide or Zidua® herbicide offers strong group 15 residual protection as both can be used prior to after soybean emergence. Outlook can be used up to V5, while Zidua can be used up to V6 soybeans. Zidua® PRO herbicide and Verdict® are multiple mode of action herbicides with enhanced weed control compared to single mode of action options but do need to be applied prior to soybean emergence.
Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.
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Endnotes
- Johnson, Bill, et al. “Biology and Management of Giant Ragweed.” Purdue Extension, www.extension.purdue.edu/extmedia/gwc/gwc-12.pdf. Accessed 18 Dec. 2024.
- Hartzler, Bob, and Brent Pringnitz. “Early-season Weed Competition.” Integrated Crop Management, Iowa State University, crops.extension.iastate.edu/encyclopedia/early-season-weed-competition. Accessed 18 Dec. 2024.
