How to manage corn and soybean crops in wet and weedy conditions

What began as an early start to the 2024 season has resulted in delayed planting for many Midwest farmers, as wet and rainy patterns settled in throughout the month of May. 

“The rains have just made for such tight windows that planters have been rolling as hard as they can,” says Matt Geiger, an agronomist with Syngenta in southern Illinois. “Spraying has taken a back seat for some growers and that’s just caused a lot of challenges with weeds emerging at the same time as the crop, which complicates things.”

The erratic spring weather has resulted in tweaks for herbicide plans on most farms, either because of delays in application from wet weather or because the size and spectrum of weeds has changed due to weather delays. 

In North Dakota, both crop and weed growth have been slow due to wet, cool, and cloudy conditions. “Once we get sun and warmer temperatures, emerging weeds are going to take off on us and the challenge will be working wet fields and trying to get those applications made,” says Joe Ikley, North Dakota State Extension weed specialist. 

Managing weeds in corn

Bill Johnson, Purdue University Extension weed science specialist, recommends scouting now to ensure the herbicide applications are still providing clean corn fields. “Giant ragweed is a big concern, but wet conditions and dilution of atrazine can result in failures to control cocklebur, sunflower, velvetleaf, burcucumber, morning glories, and waterhemp,” he says. “If corn is less than 12 inches tall and you haven’t used all of the atrazine allowed by the label, it would be wise to add atrazine to the other postemergence herbicides being applied to corn to control these weeds and provide some soil residual activity. If corn is more than 12 inches tall, you cannot use any additional atrazine.” 

Ryan Miller, University of Minnesota Extension educator for crops, echoes the need to pay attention to application cutoff dates in corn. “Some have an 11-inch cutoff and some have taller restrictions,” he says. “So make sure you're reading those labels and paying attention to your corn height.”

Managing weeds in soybeans

Geiger says there are logistical challenges when preemergent herbicides are not applied in soybeans prior to crop emergence. “If you're going to apply early postemergence herbicides instead of a pre-emergence, first you need to assess what weeds you have so you can include the appropriate tank mix partners,” he says. “Soybeans are more challenging, because many of the strong soybean chemistries need to be applied before the soybeans are up.” 

Geiger recommends considering switching to a more flexible product like Prefix which can be applied pre, at cracking, and through soybean emergence. 

Debalin Sarangi, University of Minnesota Extension weed specialist, cautions that while weed growth has been slow with the cool temperatures, the coming warmth and sun will cause weeds like waterhemp and others to grow up to an inch per day. 

“I’m suggesting they add some residual herbicide in the tank like Warrant, Outlook or Dual because I expect the waterhemp will continue emerging with the plentiful soil moisture,” says Sarangi.

Ikley, of North Dakota, reminds growers to pay attention to application cutoff dates for dicamba products in soybeans. “Most people who are using dicamba technology are probably dealing with some kochia. We still have a window here to be able to utilize that technology until June 30 for those north of I-94.” 

Cutoff dates for dicamba use vary by geography. Refer to the label for your specific region. 

For areas where dicamba restrictions do not align, Geiger recommends glufosinate, which offers tank mix flexibility with early postemergence residuals as well as crop safety. “The thing we know with glufosinate is you need good coverage, you need enough ammonium sulfate, you need to use enough carrier volume per acre with the right nozzles and then you need to mix that with your residual herbicide,” he recommends.

Carryover concerns

Johnson recommends checking rotational intervals on products like Callisto, Reflex, Stinger, and atrazine. “Once we get to June 20, then you really need to think about some of these postemergence herbicides that have residual activity and whether they’re going take you out of your crop rotation,” he cautions.