Variation in soybean (Glycine max (L.) Merr.) interference among common cocklebur (Xanthium strumarium L.) accessions

Abstract

Common cocklebur is an annual dicotyledonous weed that is extremely competitive with agronomic crops, and known to be variable for traits such as leaf and bur morphology, biomass production, and photosynthetic rate. The purpose of this study was to determine if variability of this species was manifested in its ability to reduce soybean yield. Seven common cocklebur accessions from different regions of the United States were compared over three growing seasons at Urbana, Illinois. Plots were established with each common cocklebur accession planted between soybean rows at a density of one plant per metre of row. Averaged over all accessions, soybean yield reductions were 48% and 20% in 1999 and 2001, respectively, relative to weed-free control plots. No yield reduction by common cocklebur was observed in 2000. Accession and year, but not the year by accession interaction, were significant (P<0.05) sources of variation in the 1999 and 2001 combined ANOVA for soybean yield reduction and for aboveground common cocklebur dry matter. Averaged over 1999 and 2001, soybean yield reductions ranged from 25% to 42%, depending on the accession. The amounts by which common cocklebur accessions reduced soybean yield were highly correlated (r=0.92) with their aboveground dry matter production. Variability in soybean yield-reduction potential among common cocklebur accessions makes it more difficult to develop accurate economic thresholds for managing this weed.