Studies were conducted from 1997 to 1999 at the Coastal Plain Experiment Station in Tifton, GA to measure the full-season interference of yellow nutsedge in peanut using a response prediction experiment with a natural infestation of yellow nutsedge. Seeds of cultivar Georgia Green were planted in May each year, and plots were established immediately after crop emergence. Plots were 1.8 m by 1.8 m. with six replications. Yellow nutsedge plants were counted 28 d after crop emergence in each plot, and six weed-free plots were randomly established. Parameters measured were peanut yield and yellow nutsedge tuber contamination in harvested peanut. Yellow nutsedge densities ranged from 0 to 169 plants/m². Regression analysis indicated a 25% reduction in peanut yield with a yellow nutsedge infestation of approximately 68 plants/m². Each yellow nutsedge plant/m² reduced peanut yield by 13 kg/ha. There was a positive linear response between yellow nutsedge density and number of tubers contaminating harvested peanut. Tuber contamination increased by 5190 tubers/ha for every yellow nutsedge plant/m². The results indicated that yellow nutsedge is a poor competitor with peanut. However, tuber contamination in harvested peanuts should be considered when using these results in developing treatment thresholds.