When managing weeds in soybean fields, you need a game plan encompassing the current and coming season, says Brian Weihmeir, an agronomist with LG Seeds in south-central Illinois.
That plan should also go beyond soybeans. In the Midwest where a corn/soybean rotation is common, Weihmeir emphasizes growers need to keep their corn fields clean or risk an uphill battle the following season.
Tip #1: Overlap residuals to prevent weed emergence
Weihmeir says there’s a need for a mentality shift regarding soybean weed management timing. The easiest way to keep weeds at bay is to prevent them from emerging via overlapping residuals, he says.
“Make sure you’re putting down a good pre-emergent herbicide with residual and then come back for post-application residual herbicide to take us all the way to crop canopy,” he says. Pre-emergence spraying should happen as close to planting as possible.
Tip #2: Quick canopy can keep weeds from germinating
The next major focus is keeping weeds from germinating, and that hinges on getting a quick canopy, according to Weihmeir. That should influence farmers’ row spacing and seed selections.
“Talk to your seed provider about finding the right soybeans for your farm,” he says. “If you have a light field, for example, make sure you’re talking to your seed provider about getting a soybean that gets a little bit taller and bushier so we can close the rows quicker.”
Tip #3: Walk fields and identify weeds
Palmer amaranth and waterhemp cause Midwest soybean farmers the most trouble. “They can grow an inch per day, so you might walk out in the field and hardly see anything and then come back three days later and they’re ankle-tall and we’re too late,” warns Weihmeir. Farmers need to scout fields and take a proactive approach to herbicide application.
“Pick several random areas within each field to scout and identify weeds,” Weihmeir recommends. He says farmers should also make note of weed height and be ready to tweak herbicide plans if unexpected weeds like grasses or cocklebur appear.
Tip #4: Switch up modes of action
It’s important to vary what herbicides you’re using on both corn and soybeans to stay ahead of herbicide resistance, according to Weihmeir.
This season’s supply issues could force some producers to change herbicides more than they otherwise would. It’s important to know your options if your preferred herbicide isn’t available, Weihmeir says, offering this example: “If you’re planting Enlist E3 soybeans and can’t get Liberty herbicide, know that you can also use 2,4-D or Roundup.”
Tip #5: Cover crops can suppress weeds
Producers using limited or no-till might find themselves more reliant on herbicides for soybean weed control. “That’s where cover crops come in,” says Weihmeir.
“Growers utilizing cover crops have been able to control some of our winter annuals like marestail and chickweed. Once cover crops are established, they can outcompete winter annuals. When cover crops are terminated in the spring, they also leave a nice mat that helps suppress weeds during the growing season,” he explains.
“One positive about this situation is it’s pushing farmers to look at their system a little bit closer, ask more questions and start thinking outside the box,” Weihmeir says.
