Manganese (Mn) oxidation was evaluated for Petri disease fungi by using potato dextrose agar (PDA) amended with Mn sulfate. Phaeomoniella chlamydospora showed reduced growth on PDA amended with 3000 ppm Mn sulfate and exhibited no growth at higher concentrations. All Phaeoacremonium spp. evaluated were manganese tolerant and grew on PDA amended with as much as 6000 ppm Mn sulfate. Phaeoacremonium viticola and P. angustius s.s. oxidized manganese in vitro. Stereum hirsutum and Fomitiporia punctata, known white-rot basidiomycetes, were used as controls. Stereum hirsutum oxidized Mn in vitro and grew on PDA amended with 6000 ppm Mn sulfate. Fomitiporia punctata had reduced growth at 300 ppm and no growth at higher concentrations of Mn sulfate with no clear evidence of Mn oxidation.