Phosphonate fungicides contain the active ingredient phosphite (PO₃) in various forms. Fosetyl-Al was the first phosphonate fungicide developed and is effective for control of Pythium diseases. This compound also has beneficial physiological effects and is most often used for maintenance of turf quality in creeping bentgrass putting greens during periods of heat and drought stress. Several new phosphonates, which contain potassium, sodium, or ammonium salts of phosphite, have been recently released and are marketed to turfgrass managers as fungicides or fertilizers. Field research was conducted from 2003 to 2005 to compare the effect of fosetyl-Al and phosphite salts on creeping bentgrass putting green quality when applied alone or combined with contact fungicides. Treatments included two fosetyl-Al formulations (Aliette and Signature) and 3 phosphite salt formulations (Alude, Magellan, and Magnum) applied at 9.8 kg a.i. ha^-1. The phosphonates were applied alone, combined with chlorothalonil (8.1 kg a.i. ha^-1), or combined with mancozeb (19.5 or 9.8 kg a.i. ha^-1). Plots were 1 x 1.83 m and arranged in a split-plot randomized complete block with tank-mix partners in main plots and phosphonates in subplots. Treatments were applied on 14 day intervals from early June to late August in 0.08 L m^-2 using a CO₂-powered boom sprayer. When applied alone, phosphonates did not affect turf quality in 2003 or 2004, but all formulations significantly increased turf quality in 2005 compared to untreated plots. Chlorothalonil and mancozeb applications produced the greatest increase in turfgrass quality due to their suppressive effects on algae and fungal pathogens. Signature + chlorothalonil combinations increased turf quality compared to either component applied alone in 2003 and 2005. Signature + mancozeb or Aliette + mancozeb exhibited similar effects in 2004 and 2005. Combinations of phosphite salts with chlorothalonil or mancozeb did not increase turf quality compared to chlorothalonil or mancozeb alone.