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item Williams, Martin

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2004
Publication Date: 1/2/2005
Citation: Williams, M., Ransom, C.V., Thompson, W.M. 2005. Duration of volunteer potato (solanum tuberosum l.) interference in bulb onion. Weed Science. 53(1):62-68.

Interpretive Summary: Potatoes and onions are important horticultural crops in the United States and are often grown in the same field over time. However, not all tubers are recovered from potato harvest, resulting in 'volunteer potatoes' that infest rotation crops including onions. Current weed management systems restrict the use of postemergent herbicides for volunteer potato control before the 2-lf stage of onion. The purpose of this study was to determine the effect of increasing time of volunteer potato interference on onion yield, onion bulb characteristics, and volunteer potato tuber production. Onion is highly susceptible to volunteer potato and significant yield loss occurs before onions grow 2 leaves. In addition to total yield loss, volunteer potato also reduces individual bulb size of onion, resulting in a less valuable crop. The impact of this research is several fold, including: 1) we are the first to document that volunteer potato interference causes yield loss earlier in the growing season than interference from most small-seeded annual weeds, 2) this research improves the fundamental understanding of interactions of weeds with onion, and 3) integrated weed management systems can be improved by using this new knowledge of when and how weeds affect onion yield and bulb size.

Technical Abstract: Previous research with annual weed species indicates critical timing of weed removal begins primarily after the 2-lf stage of onion, a time when postemergent herbicides can first be applied. Volunteer potato is difficult to manage and persists in western U.S. onion fields. The purpose of this research was to quantify duration of volunteer potato interference on yield and market grade of onion, as well as potato tuber production. Potato interference caused irrecoverable yield loss before the 2-lf stage of onion, with as high as 10% yield loss at 1 of 3 locations. Relative to weed-free plots, onion bulb diameter was reduced as duration of interference increased, resulting in smaller proportions of valuable bulbs. Potato produced tubers shortly after emergence which explains, in part, weed persistence despite removal of shoots with contact herbicides, cultivation, and hand-weeding in onion. Significant losses in onion yield and bulb diameter are likely given current volunteer potato management systems.