Studies were conducted in 1989 and 1990 to evaluate combinations of herbicides for control of prostrate spurge (Euphorbia humistrata Engelm. ex. Gray) in container-grown landscape plants. In 1989, the combination of Ronstar 2G [oxadiazon (2.24 kg/ha) (2.0 lb/A)] with Surflan 40 AS [oryzalin (2.24 kg/ha) (2.0 lb/A] or Barricade 65 WG [prodiamine (2.24 kg/ha) (2.0 lb/A)] resulted in 95% or better control of prostrate spurge. Combinations of Ronstar 2G [oxadiazon (2.24 kg/ha) (2.0 lb/A)] and Pennant 5G [metalochlor (4.48 kg/ha) (4.0 lb/A] or Rout 3G [oxyfluorfen (2.24 kg/ha) (2.0 lb/A) plus oryzalin (1.12 kg/ha) (1.0 lb/A)] controlled more than 80% of the weeds after 12 weeks in 1989. Some herbicide treatments containing oryzalin and pendimethalin reduced the root grade of Rhododendron cv. ‘Stewartsonian’ and Ilex crenata Thunb. ‘Helleri’ in 1990. Herbicide treatments in the 1990 study had no effect on growth parameters of Juniperus chinensis L. ‘Pfitzeriana Glauca’. Rout (oxyfluorfen plus oryzalin) was the only herbicide in the 1990 study which reduced the number of prostrate spurge plants per pot in all three landscape species after 10 weeks. Dry weight of prostrate spurge was reduced approximately 3.6 × when Rout was used on ‘Stewartsonian’ azalea. Improved prostrate spurge control due to certain herbicide combinations did not result in increased foliar growth indices of the species used in this study. Dinitroanaline herbicides should be tested further for crop phytotoxicity and potential prostrate spurge control.
A joint contribution of the University of Georgia and U.S. Department of Agriculture, Agricultural Research Service, Coastal Plain Experiment Station, Tifton, GA 31793.
3Plant Physiologist, USDA-ARS.