1610s, origin obscure; according to OED it emerged into literary speech from the talk of gardeners and farmers, perhaps ultimately from Old English blæce, blæcðu, a scrofulous skin condition and/or from Old Norse blikna "become pale." Used in a general way of agricultural diseases, sometimes with suggestion of "invisible baleful influence;" hence figurative sense of "anything which withers hopes or prospects or checks prosperity" (1828). Cf. slang blighter. Urban blight attested by 1935.