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Options for weed control in corn

Several different species of weeds can cause problems for corn growers and they vary according to geography.

Problem weeds we commonly find here in Iowa include grassy weeds such as foxtails, and woolly cupgrass. Problem broadleaf weeds are common waterhemp, sunflowers, cocklebur and velvetleaf.

Growers should know their situation before making a treatment and look at their fields to see what weeds are present. They should use an integrated pest management approach for those specific weed issues. Try to choose the product with the best potential on the weeds you have. This approach can save several dollars per acre.

Consult with a trusted retailer, or refer to a university extension Web site with weed ratings for different herbicides. Then be sure to check the herbicide product label and match up the proper herbicide for the weeds in your field.

Cultivation is still a good option, and most herbicide programs are designed for use along with cultivation. Growers can employ two different strategies for controlling weeds in corn, depending on the type of weeds present. Most grassy weeds require herbicide application either at pre-plant or during planting.

Broadleaf weed treatments may be applied in a tank mix with your grass herbicide, if field conditions favor one-pass control. However, they are typically applied postemergence.

Base or foundation herbicide - This method is used to control grasses while offering some broadleaf weed control. Examples of products to use are Keystone, FulTime, Surpass, Harness or Dual herbicide. Keystone and Hornet herbicides can also be paired together in a tank mix and used in one trip at pre-plant or planting time or else used separately. Hornet WDG herbicide is often tank-mixed with grass herbicides for broad-spectrum, one-pass broadleaf control.

Postemergence treatment - Use this method to control broadleaf weeds and some grassy weeds. Hornet applied postemerge can cover a wide spectrum of broadleaf weeds, including giant and common ragweed, cocklebur, velvetleaf, sunflowers and Canada thistle. Liberty herbicide works for both grassy weeds and broadleaves and can be applied over the top with LibertyLink hybrids.

Growers can determine the economic threshold for applying herbicides to their corn crop by consulting this this Economic Threshold for Weeds worksheet from University of Illinois. The worksheet allows growers to count the number of weeds found in a portion of the corn row. Economic values can be added in and the calculator will show growers what level of weed infestation should be treated for the maximum economic benefit per acre.

Know the in-plant trait you have planted for trait resistance, if you have them on your farm.

Whether using Liberty or Roundup Ready herbicide or CLEARFIELD Technology, map out where the trait is used in the fields. Be very careful in marking your field maps, so that each field is sprayed with the correct herbicide. After the final herbicide application is made, check for any weed escapes. Note if any spots were missed.

Record what types of weeds are present and note where they are located within the field.

Then, use this information to plan ahead for next year's crop season.

Do you have an agronomy question? Email We'll send some of the most common questions to professionals in the industry and see what they say. Look for answers in upcoming Agro-Connect Ask the Experts columns.

Several different species of weeds can cause problems for corn growers and they vary according to geography.

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