The control of blue oak (Quercus douglasii H. & A.) was investigated by cut surface applications of water-soluble amine formulations of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), 2-(2,4-5-trichlorophenoxy)propionic acid (silvex); ester formulations of 2,4,5-T and silvex; potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram); and ammonium sulfamate. All phenoxy herbicides were relatively effective in controlling blue oak; the least favorable results were obtained with undiluted ester forms of 2,4,5-T and silvex, and ammonium sulfamate. Picloram was more effective than the water-soluble amine salts of 2,4-D on both blue oak and madrone (Arbutus mensiesii Pursh). Relatively favorable results were obtained on madrone by single-point applications to stems with picloram. Applications to holes 1 inch deep were more effective than when applied in deeper or shallower holes. Diluting alkanolamine salts of 2,4-D with water and butoxyethanol ester of 2,4,5-T with diesel oil had a generally depressing effect on kill (except for the first dilution of the ester). Plant kill decreased as the diameters of the trees increased. Rainwater analyses did not furnish an explanation for the marked increase in growth of the grass beneath the treated trees.