Symptoms resembling Pythium root dysfunction have been observed on golf course putting greens established with creeping bentgrass across the southeastern United States since 2002. Root isolations from 14 golf courses yielded 59 isolates of Pythium volutum and 16 isolates of Pythium torulosum. Pathogenicity of five isolates of P. volutum, two isolates of P. torulosum, and a combination of the two species was determined by inoculating mature ‘A-1’ creeping bentgrass plants. Inoculated plants were incubated for 4 weeks at 24/16°C (day/night) to permit root infection, then temperatures were increased to 32/26°C to induce foliar symptoms. No isolates impacted root depth, root mass, or foliar disease severity after 4 weeks at 24/16°C. After increasing the temperature to 32/26°C, isolates of P. volutum induced foliar disease severity ranging from 60 to 84%, whereas isolates of P. torulosum induced only 14 to 35% disease. Isolates of P. volutum consistently reduced root mass and root depth after 4 weeks at 32/26°C, but P. torulosum exhibited no effect. These results demonstrate that P. volutum is a pathogen of mature creeping bentgrass plants. Infections that occur during cool weather reduce the growth and survival of creeping bentgrass roots during hot weather and give rise to foliar symptoms.