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item Williams, Martin

Submitted to: American Society for Horticultural Science Abstracts 2000
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2003
Publication Date: 8/1/2003
Citation: WILLIAMS, M.M. 2003. Significance of crop quality in weed competition relationships. Amer. Soc. for Hort. Sci. Abst.

Interpretive Summary:

Technical Abstract: Functional relationships used to quantify the effects of weed competition on crop yield largely fail to consider weed-induced effects on crop quality. Since weed competition reduces yield and per unit market value of some vegetable crops, a study was conducted to compare loss in both yield and market value, as influenced by weed density and duration of competition. As a model study system, dry bulb onion yield and quality response to volunteer potato density and duration of competition were quantified from field studies. A rectangular hyperbolic model is commonly used to quantify yield loss and weed density relationships. The effect of weed density approaching zero, as measured by the I parameter, had a greater impact on loss of market value than yield by an average of 47%. A logistic model is commonly used to quantify yield and duration of weed competition relationships. The duration of weed competition resulting in a 5% yield loss related to an average 10% loss in market value. Volunteer potato competition limits onion bulb size, resulting in a lower quality, less value crop. Subtle decreases in onion yield from weed competition, either as a response to weed density or duration of competition, relate to substantially larger losses in market value. When weed competition affects per unit crop market value, popular approaches used to quantify crop/weed interactions largely underestimate the actual cost of weeds.