dry rot vs dry-rot

dry rot

noun
  • The crumbly, friable decayed portions of wooden members of buildings, especially at or below grade, usually caused by a fungal infection. 

  • Any progression of decay, corruption, or obsolescence. 

  • A fungal infection which affects plants, in particular potatoes. 

dry-rot

How often have the words dry rot and dry-rot occurred in a corpus of books? (source: Google Ngram Viewer )