The south-American cordgrass, Spartina densiflora, has become the dominant plant species on recent tidal marsh restorations in the Doñana National Park (SW Spain). We examined the effect of different doses of glyphosate (720-7200 g a.i. ha(-1)) and imazamox (20-68 g a.i. ha(-1)) on growth and photosynthetic apparatus of S. densiflora. Imazamox had no effect on neither on growth nor photosynthetic apparatus of S. densiflora. On the contrary, glyphosate inhibited photochemical efficiency of photosynthesis from day one. Net photosynthetic rate, stomatal conductance and photosynthetic pigments and the number of new tillers were reduced. Glyphosate at high doses (ca. 7200 g a.i. ha(-1)) could be an appropriate method of control, since it has a negative effect over the photosynthetic apparatus and growth of S. densiflora. Furthermore, glyphosate and its main metabolite, AMPA, were not extracted from the soil, since they were retained by the very high iron and aluminum oxide content of this soil.