The use of synthetic herbicides poses a serious threat to environment, health and food safety. The development of safe and effective bioherbicides for selective control of weeds is thus the primary concern in crop production around the world. Efforts are being made to investigate the use of a safe, ecofriendly and highly selective herbicides from biological origin. Coumarin and its derivatives are natural compounds renowned for their phytotoxic potential. Mellein, a dihydroisocoumarin designated as (R)-8-hydroxy-3-methylisochroman-1-one was isolated as an active metabolite from the broth of a new strain (this strain is one of the best among phytopathogenic strains collected) of Lasiodiplodia pseudotheobromae. The structural characterization of the compound was achieved by using combined spectroscopic analysis i.e. 1D and 2D NMR and LC–MS. The host range study was carried-out against plants from Cucurbitaceae, Solanaceae and Leguminosae, Poaceae and Valerianaceae families, the isolated phytotoxic metabolite from Lasiodiplodia pseudotheobromae at a concentration 10 ?g/?l showed selective inhibition at 56%–66% against the latter two families only when inoculated. Hence, purified compound from Lasiodiplodia pseudotheobromae is recommended for large scale production of bioherbicides for the management of weeds in conventional farming to improve yield and enhance food security.