Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2005
Publication Date: March 1, 2006
Repository URL: http://www.ars.usda.gov/sp2UserFiles/Place/36221500/cswq-0236-173579.pdf
Citation: Donald, W.W. 2006. Estimated corn yields using either weed cover or rated control after preemergence herbicide. Weed Science. 54(2):373-379. Interpretive Summary: In studies of competition between weeds and crops, crop yield decreases as weed growth increases. Scientists call the shape of this decreasing relationship on a graph, a negative S-shaped or sigmoidal function, and it looks like a gently decreasing hillside. Imagine at the hilltop that weeds are few, and crop yields are high. Down in the valley, weeds choke out the crop, and yields are low. The slope of the hill represents how quickly yields decrease as weeds become more and more of a problem. The slope changes going downhill, but that change is not proportional or linear. In competition research, weeds are not usually treated with herbicides. This research addressed the following question, Do the same shaped relationships for yield loss hold when weeds survive soil residual herbicide treatment at planting? For this research, previously published data were re-analyzed to determine the relationship between corn yield and weed growth after the weeds were treated at planting with soil residual herbicides. Instead of finding the expected negative S-shaped relationship, corn yield decreased proportionately (i.e., linearly) as weed growth increased following soil residual herbicide treatment. Weed growth was measured as total weed cover (%), weed height (%), and weed volume (%), after expressing the measurements on a common basis as a percentage of the maximum observed values. This research shows that crop yield-loss equations generated in competition research in which weeds are not treated with herbicide can be very different from crop yield-loss equations found when weeds are treated with soil residual herbicides at planting. This research is of interest to weed scientists, ecologists, and agronomists who study the basis of crop-weed competition.
Technical Abstract: Because preemergence soil-residual herbicides reduce and delay annual weed emergence and decrease later weed growth, susceptible weeds surviving or recovering from herbicide treatment reduce crop yields less than do untreated weeds. Recently, corn yields were shown to be reduced differently by untreated weeds emerging in and between crop rows. However, equations have not been reported before which relate corn yields to in-row and between-row weed cover of mixed weed populations recovering from PRE soil-residual herbicides. Published data from herbicide screening research for 3 site-yrs in Missouri were reanalyzed to characterize this relationship. In-row and between-row weed cover of mixed weed populations, chiefly giant foxtail and common waterhemp, were measured from photographs at midsummer. In 2 of 3 site-yrs and the 3 site-yr average, corn yields were a nonlinear function of both in-row and between-row weed cover recovering from various PRE soil-residual herbicide treatments. In 1 of 3 site-yrs, corn yields were a nonlinear function of only between-row total weed cover.