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Angie Peltier

Angie Peltier
Former Extension Educator, Commercial Agriculture

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Hill and Furrow

Current topics about crop production in Western Illinois, including field crops research at the NWIARDC in Monmouth.
Figure. Palmer amaranth in a soybean field in Kankakee County, Illinois, 2013. The height of the plants can be compared to the mature corn in the background. (Photo credit: Dr. Aaron Hager).
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Keep a watchful eye out for Palmer amaranth during harvest

Posted by Angie Peltier - Weeds

Dr. Aaron Hager, Field Crops Weed Science Extension Specialist, recently shared some haunting pictures that he had taken of a soybean field in Kankakee County in Northeastern Illinois. Dr. Hager had received a call several weeks ago from a producer who noticed that very tall weeds had taken over the entrance of several of his soybean fields (Figure). The producer was unable to identify these weeds and hadn't noticed them in years past.

Dr. Hager made a visit to this field and identified the weed as Palmer amaranth (Amaranthus palmeri), a very aggressive, very competitive, often glyphosate-resistant, non-native weed that is closely related to waterhemp. With severe infestations, this weed has been shown to reduce soybean yields by close to 80 percent and corn yields by more than 90 percent. Dr. Hager has been warning Illinois farmers of this "waterhemp on steroids" for several years.

This year weed science researchers at the University of Illinois have offered a free service to help residents identify suspected Palmer amaranth plants using molecular techniques. Through this service and other surveys, researchers have confirmed Palmer amaranth (many times glyphosate-resistant Palmer amaranth) in Illinois counties from Massac, Pulaski, and Alexander in the far South, to Champaign and Tazewell and Cass in central Illinois and Kankakee and Will in the North. Many other counties have confirmed, suspected, or not-yet-noticed Palmer amaranth populations (click here for the map and accompanying article).

Weed scientists warn that success in battling this super-weed will only be achieved with a fundamental change in weed management philosophy. Under ideal conditions these plants can grow up to 3 inches per day. Post-emergence herbicides are recommended on Palmer amaranth plants less than 3 inches tall. It is for these reasons that weed scientists DO NOT recommend that producers rely on herbicides alone for control. Weed scientists suggest that in addition to soil-residual and post-emergence herbicides, it is also important to carefully physically remove plants from fields before flowering.

Plants have long-ago flowered and fertilized female plants will have already produced seed. During the 2013 harvest it is important to keep an eye out for Palmer amaranth. With Palmer amaranth plants, University of Illinois weed scientists suggest taking action to reduce the spread of seed within the field and decrease seed survival in a recent Bulletin article:

"1) Fields with Palmer amaranth populations should be the last fields harvested this fall and the last fields planted next spring.

2) Mark or flag areas where Palmer amaranth plants have produced seed. These areas should be intensively scouted the following season and an aggressive Palmer amaranth management plan implemented to prevent future seed production.

3) Do not mechanically harvest mature Palmer amaranth plants with crop harvesting equipment. Physically remove the plants immediately prior to harvest and either leave the plants in the field or place in a sturdy garden bag and remove the plants from the field. Bury or burn the bags in a burn barrel as soon as possible.

4) Fields in which Palmer amaranth seeds were produced should NOT be tilled during the fall or following spring. Leaving the seeds near the soil surface increases the opportunities for seed predation by various granivores."

Additional information about Palmer amaranth biology, identification and control can be found in the University of Illinois' 2012 Corn & Soybean Classics Program and the June 5th, August 6th, and September 24th Pest Management and Crop Development Crop Management Bulletin.

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