Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2012
Publication Date: 4/1/2013
Citation: Davis, A.S., Taylor, E., Haramoto, E., Renner, K. 2013. Annual post-dispersal weed seed predation in contrasting field environments. Weed Science. 61:296-302. Interpretive Summary: Reducing the reliance of weed management in field crop production may benefit from better understanding of agroecosystem services contributing to the regulation of weed population dynamics. One such agroecosystem service is postdispersal weed seed predation. After weed seeds disperse from the mother plant, many are consumed by invertebrates and small vertebrates, leading to reductions in weed seedling establishing in the following growing season. We set out to determine whether introduction of small grains and forage legumes into corn-soybean crop production systems in the north central region of the U.S. could increase rates of postdispersal weed seed predation. In a field study replicated in Illinois and Michigan from 2006 through 2008, we measured long-term weed seed predation rates in all phases of a corn-soybean-wheat/red clover crop rotation. Weed seed predation rates within three-month periods throughout the year were highly variable, with no clear support for greater predation rates in a given rotation phase. Annual predation rates were high, ranging from 50 to 80%, and depended more on local conditions than on which crop was being grown. Future efforts at managing weed seed predation rates will require site-specific knowledge to promote the activity of local granivore communities.
Technical Abstract: Interest in weed seed predation as an ecological weed management tactic has led to a growing number of investigations of agronomic and environmental effects on predation rates. Whereas the measurements in most of these studies have taken place at very short time scales, from days to weeks, measurements at longer time scales (from several months to a year) have greater relevance to the demographic impact of weed seed predation, and potential contributions from this process to ecological weed management. Our aim was to quantify the impact of crop phase, within a corn-soybean-wheat crop sequence, on quarterly and annual seed predation rates of giant foxtail, giant ragweed and velvetleaf. The study took place in contrasting areas of the northern U.S. corn belt, from the perspective of dominant land use: Savoy, IL (2005-2007), where corn and soybean production predominates, and East Lansing, MI (2005-2008), where crop production occurs within an old field/forest landscape matrix. Mean annual rates of weed seed predation by the combined action of invertebrate and vertebrate predators were 31 ± 1.6 % for giant ragweed, 37 ± 1.4 % for velvetleaf and 53 ± 1.4 % for giant foxtail. Crop phase had negligible effects upon long-term seed predation rates, accounting for less than 2 % of observed variation. Weed species and site-year, in contrast, contributed 35 % and 40 %, respectively, of the variation in cumulative annual seed predation. These results are consistent with agricultural practice: weed seed predation appears to be an inherently site-specific phenomenon. New developments in managing weed seed predation as an ecosystem service are therefore likely to have local recommendation domains.