Oxalis corniculata) in Ornamentals1

The growth regulator NAA was investigated to determine whether it would control creeping woodsorrel (Oxalis corniculata L. #3 CYPES) with no phytotoxicity to container ornamental species. Dosage, carrier volume, number of applications, and plant age and growth stage were examined as factors in the phytotoxicity of NAA. Creeping woodsorrel response to the ethyl ester formula- tion of NAA was linear for dosages up to 5.6 kg/ha; this rate resulted in about 80% injury in all experiments. NAA applied at 8.4 and 11.2 kg/ha achieved 99 and 100% con- trol, respectively. Neither carrier volume nor split appli- cations had any effect on phytotoxicity of NAA. In all experiments, phytotoxicity appeared to increase until around 2 to 3 weeks from application. Phytotoxicity to creeping woodsorrel was related to plant age; as plant age at the time of treatment increased, the level of injury decreased. When plants treated with NAA at rates up to 2.8 kg/ha were cut back to soil level, some regrowth occurred in all cases. Rates of NAA that controlled creeping woodsorrel (5.6 and 11.2 kg/ha) were not phytotoxic to several ornamental species. Additional index words. Weed control, growth regulator, auxin, OXACO.