An Etymological Dictionary of the German Language/Pilz
Pilz, m., ‘mushroom, fungus,’ from the equiv. MidHG. büleȥ (bülȥ), OHG. buliȥ (ModHG. i for ü is UpG. and MidG., as in Kitt); a specifically G. loan-word (comp. LG. bülte) from Lat. bôlêtus (Gr. βωλίτης), ‘mushroom’; probably naturalised in G. before the 7th cent., as may be inferred from the permutation of t to z (for Lat. ê, represented by OHG. î and ĭ comp. Kette and Münze). Its rare occurrence in Rom. (Grisons bulieu, Fr. bolet, Vosges bulo) supports the very early adoption of the word in HG. (comp. Pfühl).