1610s, origin obscure; according to OED it emerged into literary speech from the talk of gardeners and farmers. It is perhaps from Old English blæce, blæcðu, a scrofulous skin condition and/or from Old Norse blikna "become pale" (from the group including bleach, bleak, etc.). 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" (1660s). Compare slang blighter. Urban blight "condition of disrepair and poverty in a previously thriving part of a city" attested by 1935.