Abstract Many pecan groves throughout the south are grazed for pasture. Simazine at 3 lb/A is recommended for pastures, but the amount of residue accumulating in pecan nuts grown in pastures treated with this herbicide is not known. In this study rates of 0, 1, 2, 4, and 8 lb/A of active Simazine was applied as a spray underneath the canopy of approximately 40-year old Stuart pecan trees on March 16, 1963 while trees were dormant. Two replications were used. On November 14, a 10 lb nut sample was collected from each tree and analyzed by the Geigy Research laboratories. All samples contained less than 0.04 ppm of Simazine in both shells and kernels, which is considered essentially no residue. No damage to the trees was noticed.