Principles of Weed Threshold Research

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Abstract
Competitive and economic thresholds are distinctive and important concepts to weed scientists. The producer is most concerned about the economic threshold because of its importance in production decisions. The three additive research techniques to determine competitive weed thresholds are removal or plant-back, paired plot, and area of influence. Each method has advantages and disadvantages and must be conducted in a specific manner in the field. The area of influence technique is the most accurate for determining the influence of a single weed. Data must be reported in a usable form such as percent yield reduction. An example calculation for determining the two weed thresholds is illustrated with common cocklebur in soybeans. Generally, the economic threshold is one-half to one-third the competitive threshold.