Comparison of Ronstar Formulations for Efficacy and Phytotoxicity in Container Grown Landscape Plants

Three formulations of Ronstar [oxadiazon-2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-²-1 ,3,4-oxadiazolin-5 one], were evaluated for control of 3 weed species and injury to 3 woody landscape plants over 90 days. Wettable powder (WP) 50%, 20% granular and 0.24 kg/L (2 lb/gal) emulsifiable concentrate (EC) were evaluated at 3 rates, 2.2, 4.5 and 9.0 kg/ha (2,4 and 8 lb/A). The WP formulation was generally more effective than the G formulation for control of goosegrass [Eleusine indica (L.) Gaert] and Pennsylvania smartweed (Polygonum pensylvanicum L.). Ronstar at the 4.5 kg/ha (4 lb/A) rate of WP and EC formulations provided excellent control of goosegrass and Pennsylvania smartweed. Prostrate spurge (Euphorbia humistrata Eagelm. ex gray) was controlled only by the 9.0 kg/ha (8 lb/A) rate of all 3 formulations.

Pronounced injury to Compact Japanese Holly (Ilex crenata Thumb. ‘Compacta’) and ‘Hershey Red’ Azalea Rhododendron obtusum was evident at 14 and 30 days after treatment with the WP and EC formulations. Ninety days after treatment the species were marketable plants. Evergreen euonymus (Euonymus japonica) was not injured with any formulation or rate of Ronstar.