Palmer amaranth (Amaranthus palmeri) damage niche in Illinois soybean is seed-limited

Authors: Davis, Adam; SCHUTTE, BRIAN - New Mexico State University; HAGER, AARON - University Of Illinois; YOUNG, BRYAN - Purdue University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2015
Publication Date: 7/20/2015
Citation: Davis, A.S., Schutte, B.J., Hager, A.G., Young, B.G. 2015. Palmer amaranth (Amaranthus palmeri) damage niche in Illinois soybean is seed-limited. Weed Science. 63:658-668.

Interpretive Summary: Global change, agricultural intensification and human-aided seed dispersal are acting together to expand the range of many agricultural weed species. Palmer amaranth is currently causing heavy crop yield losses in much of the southern U.S., and is expanding its range northward. Appropriate tactics for proactively managing this weed in the upper Midwest will depend on determining where it can reduce crop yields in this region. We used a common garden study approach to compare the ability of eight populations of Palmer amaranth from the southern and Midwest U.S. to cause yield loss in Illinois soybean. Weed survival, flowering and weed biomass were measured, in addition to soybean yield and weather data. Analyses indicated that Palmer amaranth can cause soybean yield loss anywhere in Illinois. This indicates that Palmer amaranth competition in soybean in Illinois, and much of the Midwest, is limited primarily by seed immigration rate. These results highlight the urgent need for weed managers to learn Palmer amaranth identification, prevent seed introduction, and maintain a policy of zero seed-return.

Technical Abstract: Palmer amaranth, a dioecious summer annual forb originating in Sonoran desert washes, compromises crop yields in much of the southern U.S., and is expanding its range northward. Appropriate tactics for proactively managing this weed in the upper Midwest will depend on characterizing its damage niche, the geographic range in which it can reduce crop yields. We implemented a common garden study, planting eight accessions of Palmer amaranth from the southern and Midwest U.S. at a population density of eight plants/m2 into soybean crops using a biocontainment protocol in southern, central and northern Illinois in 2011 and 2012. Once Palmer amaranth plants initiated flowering, they were removed and burned. Weed survival, flowering and weed biomass were measured, in addition to soybean yield and weather data. Analyses indicated that Palmer amaranth’s damage niche in Illinois soybean was independent of weed genotype or maternal environment. Despite competing only briefly, Palmer amaranth reduced soybean yields in all site years, indicating its damage niche in Illinois, and much of the Midwest, is limited primarily by seed immigration rate. These results highlight the urgent need for weed managers to learn Palmer amaranth identification, prevent seed introduction, and maintain a policy of zero seed-return.