Ornamental Response to Two Methods of Oxadiazon Application

Abstract

Abstract Oxadiazon was applied conventionally as a granular and compared to the emulsifiable concentrate injected into sprinkler irrigation system (chemigation) at 60- day intervals on 20 species of container-grown ornamentals. In general, phytotoxicity increased proportional to the number of applications and was most prevalent during cold weather. Moderate to severe phytotoxicity at 2 × and 4 × rates was observed on aucuba (Aucuba japonica Thunb.), azalea [Rhododendron (AZ) ‘Formosa’ and R. (AZ) ‘Fashionaire’], liriope [Liriope muscari (Decne) L. H. Bailey], pampas grass [Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn.], Japanese black pine (Pinus thunbergiana Franco), and red tip photinia (Photinia ‘Fraseri’ Dress). Increased injury was observed on aucuba, Japanese black pine, and azalea when oxadiazon was applied via chemigation. On the other species, the degree of phytotoxicity was proportional to the rate applied. Both monocots showed moderate (18%) to severe (45%) injury. The only cultivar with significant growth reductions after 8 months was the ‘Formosa’ azalea when chemigated. The only species with reduced marketability due to the herbicide was liriope. After the second application, the weight and number of weeds decreased proportional to the herbicide rate or number of applications. Chemical name used: 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2(3H)-one (oxadiazon).