AimsTo identify a potential pathogenic isolate of fungus on Convolvulus arvensis and to determine its phytotoxic activity, which revealed the presence of toxic metabolites responsible for the toxicity against the target weed. Methods and ResultsA high virulent isolate of the fungus, Phoma crystallifera was isolated from symptomatic field bindweed in the west of Iran and was screened for the production of phytotoxins, which promoted necrosis on the detached leaves and seedlings of field bindweed in the bioassays. The isolate was distinct from other isolates of the fungi on the basis of morphological characteristics and the combined sequence database of the ITS region, partial LSU rDNA and -tubulin gene. Isolate P. crystalifera P6 produced the highest amount of phytotoxins after 21days in a shacked culture of Richard's broth. The active metabolites were isolated from a cell-free culture filtrate by ethyl-acetate and purified by thin layer chromatography. The result indicated that six out of nine spots had phytotoxic activity in the bioassays, with R-f values of 016, 030, 036, 043, 057 and 081. ConclusionsPhoma crystallifera P6 and its active metabolites showed significant phytotoxic effects on the detached leaves of C. arvensis. Significance and Impact of the StudyTo date, there are no reports of possible biocontrol agent(s) on C. arvensis in Iran. Thus, P. crystallifera P6 is introduced here as a severe pathogenic fungus and which can be used as a biocontrol agent against C. arvensis.