Published online by Cambridge University Press: 20 January 2017
Biennial wormwood has been increasing in Manitoba, Canada, but informationis limited on the potential of biennial wormwood to reduce crop yields.Field experiments were conducted over 5 site-yr throughout southern Manitobain 2010 and 2011 to determine the effect of biennial wormwood density andrelative time of biennial wormwood seedling recruitment on sunflower growth,development, yield, and seed quality. Biennial wormwood was broadcast on thesoil surface at six densities into sunflowers planted in 75-cm rows, eitherat the same time the sunflower crop was planted (early weed seedlingrecruitment) or when the sunflowers were at about the four-leaf stage (lateweed seedling recruitment). When biennial wormwood emerged at about the sametime as the sunflowers, yield was reduced by up to 46%. Early-recruitingbiennial wormwood had minimal effect on sunflower growth and development,but sunflower achene size and individual achene weight were reduced, evenwhen no effect on sunflower yield was observed. Biennial wormwood plantsthat recruited after the four-leaf stage of the sunflower crop had no effecton sunflower yield or seed quality.
Associate Editor for this paper: John L. Linquist, University of Nebraska.