Union carbide UC-21149 (2-methyl-2-(methylthio) propionaldehyde O -(methylcarbamoyl) oxime) was applied as a 10% granular formulation to the soil under the canopy of 2-year-old navel orange trees at rates of 1.5, 7.5, and 40.0 g active ingredient per tree. The systemic activity against several major citrus pests was measured by laboratory bioassays and field counts. When young and mature leaves were collected at frequent intervals and test arthropods were permitted to feed on them in the laboratory for 3 days, the citrus red mite, Panonychus citri (McGregor), was the most susceptible, the California red scale, Aonidiella aurantii (Maskell), next, and. the citrus thrips, Scirtothrips citri (Moulton), least. The 2 higher doses effectively controlled field populations of the citrus red mite for 44 weeks, the spirea aphid, Aphis spiraecola Patch, for 29 weeks, and the citrus thrips for 10 weeks. Fruit collected at 100 days posttreatment contained no residues of UC-21149. The sulfoxide residues in the peel and fruit pulp from trees receiving the highest dose were 12.75 and 2.63 ppm, respectively. In the same fruit, the sulfone residues in the peel and pulp amounted to 2.24 and 0.58 ppm, respectively. No evidence of phytotoxicity was seen in any tree. This compound shows considerable promise for controlling the 3 major pests of nonbearing citrus trees.