At this year’s Blackands Farm Managers Tour at Green Valley Farms near Columbia, N.C., Wes Everman once again emphasized the critical importance of controlling weeds in corn early in order to maximize yields.

“Once we get corn up and going, it can compete well with weeds. It’s early season competition where we run into some challenges,” said Everman, North Carolina State University Extension weed specialist.

“We typically recommend a PRE up front and then recommend coming  back with a timely post. If those weeds come up with the crop and they’re competing and they get up to over four inches tall, we start seeing yield reduction,” Everman said.

Timely spraying in the spring is vital. “Corn is one of the crops we can do a good job managing palmer, ragweed and other broadleaf weeds we’re seeing resistance to,” he said.

To emphasize the importance of timely spraying, Everman cited research conducted at N.C. State that shows how weeds can take up available nitrogen fertilizer and impact corn yields. In the research, nitrogen was applied at 60 pounds up to 180 pounds per acre up front.

Everman noted that after the fertilizer was applied, weed species went out and found nitrogen. The roots of the weed became bigger and they were more competitive, taking up anywhere between 20 to 40 pounds of nitrogen per acre, even when small.

“But if we put out that same nitrogen and let those weeds get to about 9 inches tall, we were seeing weeds take up 80 to 100 pounds of nitrogen depending on what weed species were present and what the density was. There’s a reason it’s impacting your yields; it’s taking away your nitrogen,” Everman said.

Farmers could add more fertilizer, but that’s expensive. Everman said the better strategy is to make a timely post herbicide application to control weeds when they are small. “If you have soils that take PREs and you can use PREs effectively, a good PRE program frees up a lot of time to spray those weeds post. If you don’t use PREs and rely on posts exclusively, make sure you’re timely.”

For post programs in corn, Everman is recommending HPPD inhibitors, mainly because they aren’t used in other crops. “It gives us a different mode of action,” he said. Everman also said atrazine is an important part of the post mix.

“Pick one that’s good for your weeds. Most corn products out there are quite effective and there are good programs all around,” Everman said.