Phosphonate fungicides are used to control Pythium blight on golf course turf, yet little information exists concerning efficacy differences between phosphite and fosetyl-Al products. This study was designed to determine the effects of different formulations of phosphite and fosetyl-Al fungicides on control of Pythium blight (caused by P. aphanidermatum) in ‘Penncross' creeping bentgrass (Agrostis stolonifera L.) and ‘Integra' perennial ryegrass (Lolium perenne L). Two phosphite treatments (Alude fungicide and a reagent grade phosphite standard), two fosetyl-Al fungicides (Signature and Aliette), mefenoxam (Subdue MAXX), a reagent grade phosphate control; and an untreated control were compared in a field trial in University Park, PA. The experiment was conducted in a temperature- and humidity-controlled chamber from 30 Aug 2004 to 13 Sep 2004. Phosphonate treatments were applied to turf at 3.63kg P/ha two days prior to inoculation with P. aphanidermatum. This factorial experiment was arranged as a randomized complete strip-block design with four replications. Disease assessments (% blighting) were made 14 days after treatment application. Disease symptoms were more severe on perennial ryegrass than creeping bentgrass and all fungicide treatments provided better control of Pythium blight on creeping bentgrass than perennial ryegrass. All fungicide treatments provided good control (>89%) of Pythium blight on creeping bentgrass and perennial ryegrass, relative to the untreated control and the phosphate control. On creeping bentgrass, no differences were detected among mefenoxam, the two fosetyl-Al fungicides, or the two phosphite treatments. On perennial ryegrass, mefenoxam provided better control of Pythium blight than the reagent grade phosphite and Alude, but was not different from Aliette and Signature.