According to Wikipedia:

Blight refers to a specific symptom that can be expressed by plants in response to infection by a plant pathogenic organism. It is simply a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs.^[1] Accordingly, many diseases that primarily exhibit this symptom are called blights.

Further searches of Wikipedia yield the following:

Urban Blight is a process by which a city, or a part of a city, falls into a state of disrepair. It is characterized by depopulation, property abandonment, high unemployment, fragmented families, political disenfranchisement, crime, and desolate and unfriendly urban landscapes.