Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2006
Publication Date: 1/1/2007
Citation: Williams, M., Ransom, C.V., Thompson, W.M. 2007. Volunteer potato density influences critical time of weed removal in bulb onion. Weed Technology. 21(1):136-140. Interpretive Summary: Onion is one of the most sensitive crops to weed interference. Recent research has quantified important thresholds to managing weeds in onion, specifically in terms of weed density and duration of weed interference. Since weed species abundance is field-specific, field studies were used to quantify potential interactions between volunteer potato density and removal time of the weed. As weed density increases, the onset of competition occurs earlier; for volunteer potato in onion, the onset of competition can occur at a time before postemergent herbicides can be used. The impact of this research is that stages of the life cycle of volunteer potato, besides emerging plants, should be targeted to reduce weed interference in bulb onion.
Technical Abstract: Volunteer potato is highly competitive with onion and few control tactics are effective for removing the weed from an onion crop. Both volunteer potato density and duration of interference reduce onion yield, but the interaction of these factors is unknown. Field trials were conducted in Idaho, Oregon, and Washington to determine the influence of volunteer potato density on the critical time of weed removal in onion. Yield losses of 2.5, 5.0, and 10% were estimated to occur at 534, 654, and 830 growing degree days (GDD) after onion emergence, respectively, with a volunteer potato density of 0.5 plants m-2. At 2.0 volunteer potato plants m-2, yield losses of 2.5, 5.0, and 10% were estimated to occur at 388, 481, and 598 GDD after onion emergence, respectively. Volunteer potato at 2.0 plants m-2 had to be removed at least one onion leaf stage sooner, compared to a weed density of 0.5 weeds m-2, to avoid yield loss. Lowering potato tuber densities in crops preceding onion will extend the critical time for weed removal and reduce the risk of crop loss.