DENSITY EQUIVALENT - A METHOD FOR FORECASTING YIELD LOSS CAUSED BY MIXED WEED POPULATIONS

A method to evaluate potential crop damage from multi-species weed inf estations is presented. The method is based on the hyperbolic relation ships between density of a single weed species and crop yield loss. Wh en considering a mixed weed population, the density of each species is transformed into a Density Equivalent, defined as the density that is equal to the density of a reference species giving the same yield los s. A hypothetical species with i and a parameters both equal to 100 wa s adopted to describe the relationship between yield and reference den sity. The method has been evaluated with data from a 2-year experiment on soybean (Glycine mar (L.) Merril) grown in mixtures with Xanthium strumarium L. subsp. italicum, Polygonum persicaria L. and Panicum mil iaceum L. The mixtures included seven weed densities with different pr oportions of the three weed species. The model described the data well , but it showed an average 7.5% overestimation of crop damage. The rea sons for this overestimation and the utility of the model in weed mana gement is discussed.