Typhula incarnata (GSM) and Microdochium nivale (PSM) are important psychrophilic pathogens of cool-season turfgrasses. Existing field data suggests that K fertilization may affect disease severity, warranting additional experimentation under controlled conditions. Overwintering carbon metabolism of perennial grasses is known to affect their performance and utility. While there is some evidence that plant K status influences winter survival, the physiological basis is unclear. The goal of this project was to determine the effect of K fertilization on carbon metabolism of overwintering annual bluegrass [Poa annua var. reptans (Hauskn) Timm.] and its relationship to psychrophilic pathogen susceptibility. In a greenhouse, annual bluegrass was seeded into 30 x 10 cm diam. sand filled columns. Nitrogen (0.5 g m2), K (0.5 g m2), and all other plant essential nutrients were applied weekly for 90 d. Following establishment, weekly application rates of N and other essential nutrients remained constant, yet five different K treatments (0, 0.25, 0.5, 2, 3 g m-2) were imposed for 90 d. Columns were then moved to a refrigerated room, maintained under a photosynthetically active radiation flux of ~300 [MICRO SIGN]mol m-2 s-1, and day/night air temperature incrementally decreased every 7 d over four weeks (10/4°C, 4/-2°C, 2/-4°C, -2/-6°C). Plants were then buried under 10 cm of snow and kept under darkness at -4°C for 28 d. After thawing at 2°C, eight replicates of each K treatment were inoculated with a 5 mm agar disc taken from GSM, PSM, or sterile cultures. Columns were incubated at 2°C (40 d) then 4°C (40 d) under periodic misting and evaluated for % necrotic turf every 10 d. Survival analysis of days to 50% infection (LI50) was used to quantify disease progression. Tissue harvested following each experimental phase was analyzed for nonacid cations, nonstructural carbohydrates, and several organic acids using gas chromatography-mass spectrometry. The experiment was conducted twice and data was pooled. Potassium treatment significantly affected LI50 in GSM (Pr>[chi]2 =0.007) but not PSM (Pr>[chi]2 =0.277) inoculated turf. While specific mechanisms remain unclear, several biochemical parameters (K, Ca, organic acid content) associated with GSM and PSM severity were impacted by K fertilization rate. In contrast to existing literature, nonstructural carbohydrate dynamics were not strongly correlated with disease severity. Disease recovery was significantly slower for PSM inoculated turf than GSM inoculated turf. Tissue K content and cation:anion ratios increased with K fertilization rate. Overall K fertilization had a minimal impact on non-structural carbohydrate dynamics. Tissue organic acid content, particularly malate and citrate, markedly increased at greater K fertilization rates. The results of this study suggest that K fertilization significantly increases diversion of carbon resources to organic acid synthesis due to perturbations in charge and pH homeostasis associated with disparate cation/anion uptake ratios. In addition to affecting plant utility, there is a biochemical cost associated with luxury K uptake and subsequent organic acid accumulation.