Field and greenhouse experiments were conducted in 2005 and 2006 in Guam to evaluate the effects of glyphosate on field dodder control and to describe glyphosate dose–response curves on selected ornamental plants grown with and without dodder infestation. Visual quality of dodder-free plants decreased with increasing dose of glyphosate. The most sensitive species was king's mantle, whereas the most tolerant was hibiscus. The values for the effective dose for a 10% reduction in visual quality (ED10) of glyphosate were 800, 280, 1,250, 370, 590, 830, 660, and 170 g ai/ha for dodder-free croton, allamanda, hibiscus, paper gardenia, ixora, duranta, schefflera, and king's mantle, respectively. However, dodder-infested plants were less tolerant to glyphosate because of the confounded stress from both the parasite and herbicide. Field dodder parasitizing ornamental plants could be adequately controlled on all ornamental species at a dose of about 140 g/ha of glyphosate.
Nomenclature: Glyphosate, N-(phosphonomethyl)glycine, field dodder, Cuscuta campestris Y. CVCCA, duranta, Duranta L. spp., garden croton, Codiaeum variegatum (L.) Blume, hibiscus, Hibiscus L. spp., ixora, Ixora L. spp., king's mantle, Thunbergia erecta (Benth.) T. Anders., miniature schefflera, Schefflera arboricola (Hayata) Merr., paper gardenia, Tabernaemontana divaricata (L.) R. Br. ex Roemer & J.A. Schultes, purple allamanda, Allamanda blanchetii A. DC