has been mildewing

• present perfect progressive

  present perfect progressive

  Used to describe an action that began in the past, has continued continuously, and is still in progress.

  of mildew (3rd person singular).
  mildew

  noun

  a disease of plants, characterized by a cottony, usually whitish coating on the surface of affected parts, caused by any of various fungi.

Related Words

• blight
• mold