Chlorophyll fluorescence analysis (CFA) has been successfully used to rapidly determine the responses of different plants to herbicides. It has not, however, been used to test the effect of these products on invasive riparian species. This paper reports the use of CFA to determine photosynthetic activity in Arundo donax, an invasive reed causing serious problems in Mediterranean riparian habitats, in response to systemic herbicide application following cutting. Growth was measured in terms of new sprout relative height and sprout and rhizome relative biomass. CFA showed glyphosate, from half the on-label dose of 5 L ai.ha(-1)upwards, to have a significant effect (100% reduction) on photosynthetic activity at 21 days after treatment (DAT), while profoxydim, from half the on-label dose of 0.375 L ai.ha(-1)upwards, caused a 70% reduction soon after application, although these plants later recovered. Azimsulfuron, cyhalofop-butyl and penoxsulam had no significant effect on photosynthetic activity at any dose. At 60 DAT, glyphosate (from half the on-label dose of 5 L ai.ha(-1)upwards) was associated with a 90% reduction in sprout height, while profoxydim (from half the on-label dose of 0.375 L ai.ha(-1)upwards) caused a 50% reduction. No dose (0-2x the on-label dose) of azimsulfuron, penoxsulam or cyhalofop-butyl was associated with any significant growth reduction at 60 DAT. The results show that CFA can be used to successfully measure the response of these invasive plants to herbicides, and that glyphosate, and possibly profoxydim, might be used to control Arundo donax after initial cutting.