DIMBOA (2,4-dihydroxy-7-methoxy-1,4(2H)-benzoxazin-3-one), a corn (maize) secondary metabolite, is lethal to the cells of tobacco, carrot root slices and to both DIMBOA-producing (B73) and non-producing (bxbx) varieties of corn. Application of DIMBOA to wounded tobacco leaf petioles causes a black lesion and shrivelling of the whole leaf, presumably resulting from death of DIMBOA-treated cells and subsequently uneven growth of the leaf blade. Microscopic examination reveals that DIMBOA treatment causes plasmolysis, cell collapse and disruption of cells. DIMBOA also causes browning and necrosis in the leaf-spot assay on tobacco and on high- and low-DIMBOA varieties of corn. MBOA, a degradation product of DIMBOA, does not cause significant damage to the corn leaf.