A new phytotoxic hexasubstituted pyranopyran, biscopyran, was isolated together with phenylacetic acid and previously isolated 5-methylmellein from the liq. culture filtrates of Biscogniauxia mediterranea, a major fungal pathogen involved in oak decline in Sardinia. Biscopyran was characterized by spectroscopic methods as a new (Z)-2-methoxy-1-[7-((Z)-2-methoxybut-2-enoyl)-3,4,5,6-tetramethyl-2H,7H-pyrano[2,3-b]pyran-2-yl]but-2-en-1-one. Biscopyran assayed at 0.26-0.026 mM concn. range caused epinasty on cork oak cuttings. On a nonhost plant, tomato, biscopyran caused wilting. Phenylacetic acid, assayed at the same concn., was toxic to Quercus suber, while on tomato cuttings it induced internal tissue collapse on the stem.