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Northern Illinois Agriculture

University of Illinois Extension
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Scouting weeds pre-harvest

Posted by Russel Higgins - Weeds

In a recent Bulletin article Dr. Aaron Hager, University of Illinois Weed specialist reminds farmers to be alert for amaranth or pigweed species in your fields.

In his article Dr. Hager shared that identification of the various species becomes much more reliable when reproductive structures are present. Before harvest begins, consider taking a few minutes to scout fields; at this time of year it is much easier to differentiate between Palmer amaranth and Waterhemp plants, Similar to Waterhemp, Palmer amaranth plants are either male or female; male plants produce only pollen while female plants produce only seed. Most seeds on female plants already have attained their mature black color, although some seeds may still be dark brown.

A key identifying characteristic between Waterhemp and Palmer, The terminal inflorescence of male and female Palmer amaranth plants is generally unbranched and very long. The Inflorescence of a female Palmer amaranth is measured not in inches but in feet. In

This week my travels took me through Kankakee and Will Counties and I can attest to the ease of recognizing Palmer amaranth at this stage of the growing season.

If you find a limited area infested with Palmer, it is our recommendation to leave the area unharvested. The combine serves as a very efficient weed seed distributor. This will likely result in an expanded area with Palmer amaranth in successive years. Allow the limited area to stand and plan an aggressive management program for next year to eliminate future emerged plants and prevent the spread of this troublesome weed throughout the field.

In areas of northern Illinois who are fortunate and do not have populations of Palmer amaranth, it is still important to observe different weed species that were not effectively controlled by their 2014 herbicide programs. Glyphosate resistant Waterhemp has been confirmed in several northern Illinois Counties, and we will be collecting seed from Giant ragweed for greenhouse testing this winter. Understanding 2014 weed issues will aid in your 2015 weed management decisions.

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