COLUMBIA, Mo. – Corn growers might want to review ways to avoid atrazine runoff after the heavy rains this past spring.

Bob Broz, a University of Missouri Extension water quality specialist, said this spring’s rains in claypan regions put lakes and rivers at risk of atrazine runoff in some watersheds. More than half of the state contains claypan or claypanlike soil that absorbs water slowly when wet and swollen.

Atrazine, which is a popular and inexpensive weed control herbicide, is used on approximately 85 percent of the state’s cornfields. It is one of the most effective water-soluble herbicides on the market. It costs about $20 less per acre than similar products, Broz said.

Timing, intensity and duration of rainfall all affect runoff. Farmers can’t control rain, but Broz said they can manage the land to prevent or reduce runoff.

Several Missouri watersheds are being studied under the Environmental Protection Agency’s Atrazine Ecological Monitoring Program, a partnership between the EPA and pesticide manufacturers. The group monitors atrazine runoff, and the EPA can limit or prohibit its use in watersheds exceeding set limits or those the EPA deems at risk, Broz said.

Two of the watersheds, Honey Creek Watershed in Clark County and the West Fork Watershed in Audrain and Montgomery counties, exceeded the ecological triggers on allowable atrazine in water last year.

Broz and others at MU study and teach ways to reduce runoff. Last year, specialists held 66 meetings to teach best practices to more than 1,300 people.

Extension works with the Missouri Corn Growers Association, Syngenta Corporation, the Agriculture Research Service and others to teach farmers to safely and effectively use atrazine.

MU Extension created a DVD and PowerPoint presentation to help farmers learn ways to reduce runoff. The DVD and PowerPoint are available through most county extension offices or by contacting Broz at 573-882-0085.

Broz gave these tips to manage atrazine runoff:

• Follow label instructions.

• Consider the weather before applying atrazine. If possible, apply at least two days before rainfall.

• Understand setback distances of fields to water sources.

• Understand soil types before applying atrazine.

• Look at farming systems including crop rotation and buffers before applying atrazine.

• Consider using a split application program: one application in early spring and another later in the summer with smaller amounts of atrazine each time.

• Consider applying atrazine at lower rates.

• Use the correct equipment and make sure it’s calibrated properly.

• Evaluate fields by using a field-by-field map of your farm. Note water sources, drainage patterns, wells and sinkholes, erodible land and other areas of concern.


For more information, read MU Extension publication G4851, Atrazine, Best Management Practices and Alternatives in Missouri, at

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