Controlling Weeds Through Canopy

Controlling Weeds Through Canopy

Weeds might try to make a home in the same field as your corn, but certainly not as invited guests. We know weeds can hurt corn yields by competing for vital nutrients, sunlight and moisture.

What’s less clear is exactly when that competition crosses over to yield loss.

A growing body of university research sheds light on just how much weeds can hurt yields for each day they go uncontrolled. Universities are also discovering that there might be more to weed competition and control than we typically think.

  • University of Nebraska-Lincoln defined a "critical period of weed control"
  • Iowa State University found 3- 4- inch weeds can reduce yields by 3 bu/A for every day they are uncontrolled.
  • Corn & Soybean Digest reported South Dakota State University researchers saw as much as 40 bu/A corn yield lost due to early season weed competition.
  • The Ohio State University reported planting happens earlier in the season now than it did 25 years ago. Researchers say this poses different challenges when it comes to achieving season-long weed control, and they identify four considerations to keep in mind when making weed control decisions.
  • There might be more to weed competition than nutrients, light and moisture, though. No-Till Farmer reported on a study that suggested “corn may actually react negatively to ‘ seeing’ a weed nearby.”

From Early Season to Season-Long

Of course, weed control doesn’t stop with the early season. As Jody Wynia, corn marketing manager for Crop Science explains, early season control is vital to keep fields weed-free all season.

“The best way to manage weeds for a full season is to get ahead of them,” Wynia said. “And that starts by getting out there when the weeds are young.

“Consider how quickly some of these weeds grow and how many seeds they produce. If you have to try to catch up with your weeds, you’ll play catch up all season.”

Firsthand Experiences

John Anson of Andrews, Ind., has always been concerned with controlling weeds in his corn as early as possible and throughout the season.

“When it comes to weed control in my fields,” Anson explained, “I’m looking for the clean field through the whole season. We just feel keeping the corn fields clean gives us better yield.”

Unfortunately, many postemergence herbicides don’t offer the residual needed to really control weeds through canopy. Chris Thorp of Gibson City, Ill., discussed his experiences with season-long weed control, particularly with postemergence herbicides.

“We haven't been using a residual chemistry in our second application ,” Thorp said, “and we needed to find a product to do that.”

Anson and Thorp found the answer to season-long weed control with Capreno® herbicide. Anson applies Capreno early enough in the season that it works for him in a single pass. Thorp tankmixes Capreno with glyphosate and applies them as the second pass of a pre/post herbicide program.

“Capreno works really well on weed control in our area,” Anson said.

“Capreno seemed to be a lot safer spraying at the post timeframe we followed,” Anson added. “I felt that the corn was less brittle and less green snap after we sprayed and the corn seemed to be very safe if a storm came through.”

When it comes to weed control in his fields, Thorp looked back to his 2013 crop season as an example.

“We had a pretty nasty outbreak of marestail in our standing corn, which was getting too tall to use other chemistries,” Thorp said. “We put Capreno out as our second trip, and we were just blown away by the control we received.”

For more information about season-long weed control, check with your retailer, local Extension office or a Crop Science representative.

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