Involved in momilactone phytoalexins biosynthesis; acts as a multifunctional diterpene oxidase. Participates in the biosynthetic steps between 9-beta-pimara-7,15-diene and 3-beta-hydroxy-9-beta-pimara-7,15-dien-19,6-beta-olide. Catalyzes also consecutive oxidations at C19 of syn-stemod-13(17)-ene. 9beta-pimara-7,15-diene + 3 O2 + 3 reduced [NADPH--hemoprotein reductase] = 9beta-pimara-7,15-dien-19-oate + 4 H(+) + 4 H2O + 3 oxidized [NADPH--hemoprotein reductase] kcat is 46 sec(-1) with syn-pimaradiene as substrate and 49 sec(-1) with syn-stemodene as substrate. By chitin oligosaccharide elicitor and jasmonic acid (MeJA). 3-beta-hydroxy-9-beta-pimara-7,15-dien-19,6-beta-olide is a precursor of the phytoalexins momilactones A and B. Phytoalexins are diterpenoid secondary metabolites involved in the defense mechanism of the plant and produced in response to attack (by a pathogen, elicitor or UV irradiation). Momilactone B can also act as an allochemical (an antimicrobial and allelopathic agent), being constitutively produced in the root of the plant and secreted to the rhizosphere where it suppresses the growth of neighboring plants and soil microorganisms. Belongs to the cytochrome P450 family. Truncated N-terminus. Truncated N-terminus.