Wallaces Farmer

Advice on minimizing herbicide drift, applying sidedress N to corn and controlling weeds in new dicamba-resistant soybean varieties.

Rod Swoboda 1, Editor, Wallaces Farmer

June 10, 2016

4 Min Read

Most of the corn in Iowa right now is around V3 to V6 growth stage. Some of the replant corn is now emerging or “popping up” with the heat. “I think and hope I saw my last replanted corn being planted on June 6. It was planted in some wet spots that had dried out on the edges of some bottom fields,” says Iowa State University Extension field agronomist Clarke McGrath, who covers parts of western and southwest Iowa.


This week he’s been fielding questions from farmers regarding how to minimize herbicide drift, how to decide whether corn needs some sidedress nitrogen, and how to control weeds in the new dicamba-resistant soybean varieties which aren’t yet labeled for application of dicamba herbicides.

1) Avoid or minimize problems with herbicide drift

A lot of corn herbicide spraying is going on in the countryside these days, and of course, as always, it is windy this time of year. Hopefully sprayer operators can get out early in the morning and towards evening on the windiest days to help minimize drift issues.

“Having run a co-op custom spraying operation for nearly a decade, I know all of this is easier said than done. However, using buffer zones, drift agents and low drift nozzles will help a lot,” says McGrath. “Good luck with getting the corn spraying wrapped up, and then we can head into bean spraying.”

2) Change tip size if sprayer speed has increased

Increasing sprayer travel speed causes the controller to increase boom pressure (and decrease droplet size). Mark Hanna, an ISU Extension ag engineer and sprayer expert, offers the following advice.

If field conditions have you running behind and your sprayer travel speed has increased 20% to 25%, consider using one size larger nozzle tip to minimize drift potential. For example, if self-propelled sprayer speed increases from 12 to 15 miles per hour and #4 tips are used at 12 miles per hour, substituting #5 tips at 15 miles per hour allows similar boom pressure to what was used with #4 tips at 12 miles per hour.

Related articles: Click on these helpful articles for more specific information:

* Sprayer Speed Affects Drift Potential

* Spray Drift Potential Increases During Warm Weather Applications

* Spray Volume is Critical for Postemergence Herbicides

* Selecting Nozzles for Postemergence Herbicides

3) Should you apply additional nitrogen to this year’s corn?

McGrath is seeing a lot of “wavy” or up and down corn plants in fields, and light to dark colored green corn in many fields, with some showing patterns related to tillage and/or anhydrous application. “We tend to see more of this in cool, wet springs,” he says. “I think a lot of it has to do with slower mineralization of soil nitrogen. Typically this is transient and as we get warmer temperatures, a little drier weather, and deeper root growth, things usually even out. We’ve seen a few fields this spring where it’s pretty profound and growers are wondering if applying additional N will help out. This is a hard question to answer, and as usual, I preface anything related to this with “it depends.”

ISU Extension soil fertility specialist John Sawyer recently authored an ICM Blog with good insight on the issue: Precipitation and nitrogen this spring. Also, read this related ICM News article from 2014, titledEstimating Nitrogen Losses in Wet Corn Fields.

4) Dicamba resistant soybeans are raising questions

McGrath has a number of farmers as clients who gave the new dicamba resistant soybeans a try this year, and now they are starting to think about weed management in those bean varieties. “Remember, EPA has not given clearance to spraying dicamba of any type on these beans,” says McGrath. “Hopefully, next year we can give dicamba herbicide a try as we hope EPA will have granted the label approval by then.”

What can you do with weeds coming in dicamba resistant beans today? “About all we can do right now related to dicamba is use these genetics as a chance to hit weeds in waterways, terraces and fencerows harder than usual,” says McGrath. “We can use labeled dicamba applications in these non-crop areas, and, the good news is, if we are next to dicamba resistant beans we won’t see the typical herbicide injury symptoms that often accompany broadleaf control in the non-crop areas adjacent to soybeans.”

Caution: “Please don’t hang a boom out into these beans,” says McGrath. “That would be an off label application of dicamba, and I don’t want any farmers to be on the EPA’s radar over any mistakes made with this new technology!”

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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